v3.10.0.1
Segment and Related Information - Financial Data for Business Segments and Products and Services (Details)
 3 Months Ended 6 Months Ended 10 Months Ended 12 Months Ended
Dec. 31, 2018
USD ($)
utility
Sep. 30, 2018
USD ($)
Jun. 30, 2018
USD ($)
Mar. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Sep. 30, 2017
USD ($)
Jun. 30, 2017
USD ($)
Mar. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Jun. 30, 2016
USD ($)
Oct. 31, 2016
USD ($)
Dec. 31, 2018
USD ($)
utility
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Segment Reporting Information [Line Items]                            
Total operating revenues                       $ 23,495,000,000 $ 23,031,000,000 $ 19,896,000,000
Depreciation and amortization                       3,131,000,000 3,010,000,000 2,502,000,000
Interest income                       38,000,000 26,000,000 20,000,000
Earnings from equity method investments                     $ 15,000,000 148,000,000 106,000,000 59,000,000
Interest expense                       1,842,000,000 1,694,000,000 1,317,000,000
Income taxes                       449,000,000 142,000,000 951,000,000
Segment net income (loss) $ 269,000,000 $ 1,222,000,000 $ (127,000,000) $ 936,000,000 $ 500,000,000 $ 1,109,000,000 $ (1,348,000,000) $ 665,000,000       2,226,000,000 842,000,000 2,448,000,000
Goodwill 5,315,000,000       6,268,000,000       $ 6,251,000,000     5,315,000,000 6,268,000,000 6,251,000,000
Total Assets 116,914,000,000       111,005,000,000       109,697,000,000     116,914,000,000 111,005,000,000 109,697,000,000
Gross property additions                       8,205,000,000 5,984,000,000 7,624,000,000
Depreciation and amortization                       3,549,000,000 3,457,000,000 2,923,000,000
Operating Income 578,000,000 2,174,000,000 63,000,000 1,376,000,000 739,000,000 1,991,000,000 (1,649,000,000) 1,252,000,000       4,191,000,000 2,333,000,000 4,486,000,000
Segment and Related Information (Textual) [Abstract]                            
Estimated loss on plants under construction                       1,097,000,000 3,362,000,000 428,000,000
Impairment charges                       210,000,000 0 0
Gain (loss) on asset sales                       301,000,000 42,000,000 2,000,000
Goodwill impairment 0                     42,000,000    
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)         264,000,000                  
Kemper IGCC                            
Segment and Related Information (Textual) [Abstract]                            
After tax charge to income                       722,000,000 2,400,000,000 264,000,000
Plant Scherer Unit 3                            
Segment and Related Information (Textual) [Abstract]                            
After tax charge to income               20,000,000            
Pre-tax charge to income               33,000,000            
Electric Utilities                            
Segment Reporting Information [Line Items]                            
Total operating revenues                       18,571,000,000 18,540,000,000 17,941,000,000
Depreciation and amortization                       2,565,000,000 2,457,000,000 2,233,000,000
Interest income                       31,000,000 21,000,000 13,000,000
Earnings from equity method investments                       (1,000,000) 1,000,000 2,000,000
Interest expense                       1,035,000,000 1,011,000,000 931,000,000
Income taxes                       207,000,000 82,000,000 1,091,000,000
Segment net income (loss)                       2,304,000,000 878,000,000 2,571,000,000
Goodwill 2,000,000       2,000,000       2,000,000     2,000,000 2,000,000 2,000,000
Total Assets 93,959,000,000       87,085,000,000       86,994,000,000     93,959,000,000 87,085,000,000 86,994,000,000
Gross property additions                       6,392,000,000 4,104,000,000 6,966,000,000
Traditional Operating Companies                            
Segment and Related Information (Textual) [Abstract]                            
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)                         367,000,000  
Traditional Operating Companies | Electric Utilities                            
Segment Reporting Information [Line Items]                            
Total operating revenues                       16,843,000,000 16,884,000,000 16,803,000,000
Depreciation and amortization                       2,072,000,000 1,954,000,000 1,881,000,000
Interest income                       23,000,000 14,000,000 6,000,000
Earnings from equity method investments                       (1,000,000) 1,000,000 2,000,000
Interest expense                       852,000,000 820,000,000 814,000,000
Income taxes                       371,000,000 1,021,000,000 1,286,000,000
Segment net income (loss)                       2,117,000,000 (193,000,000) 2,233,000,000
Goodwill 0       0       0     0 0 0
Total Assets 79,382,000,000       72,204,000,000       72,141,000,000     79,382,000,000 72,204,000,000 72,141,000,000
Gross property additions                       6,077,000,000 3,836,000,000 4,852,000,000
Southern Power                            
Segment and Related Information (Textual) [Abstract]                            
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)                         743,000,000  
Southern Power | Electric Utilities                            
Segment Reporting Information [Line Items]                            
Total operating revenues                       2,205,000,000 2,075,000,000 1,577,000,000
Depreciation and amortization                       493,000,000 503,000,000 352,000,000
Interest income                       8,000,000 7,000,000 7,000,000
Earnings from equity method investments                       0 0 0
Interest expense                       183,000,000 191,000,000 117,000,000
Income taxes                       (164,000,000) (939,000,000) (195,000,000)
Segment net income (loss)                       187,000,000 1,071,000,000 338,000,000
Goodwill 2,000,000       2,000,000       2,000,000     2,000,000 2,000,000 2,000,000
Total Assets 14,883,000,000       15,206,000,000       15,169,000,000     14,883,000,000 15,206,000,000 15,169,000,000
Gross property additions                       315,000,000 268,000,000 2,114,000,000
Southern Company Gas                            
Segment Reporting Information [Line Items]                            
Total operating revenues                       3,909,000,000 3,920,000,000 1,652,000,000
Depreciation and amortization                       500,000,000 501,000,000 238,000,000
Interest income                       4,000,000 3,000,000 2,000,000
Earnings from equity method investments                       148,000,000 106,000,000 60,000,000
Interest expense                       228,000,000 200,000,000 81,000,000
Income taxes                       464,000,000 367,000,000 76,000,000
Segment net income (loss)                       372,000,000 243,000,000 114,000,000
Goodwill 5,015,000,000       5,967,000,000       5,967,000,000     5,015,000,000 5,967,000,000 5,967,000,000
Total Assets 21,448,000,000       22,987,000,000       21,853,000,000     21,448,000,000 22,987,000,000 21,853,000,000
Gross property additions                       1,399,000,000 1,525,000,000 618,000,000
Segment and Related Information (Textual) [Abstract]                            
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)                         93,000,000  
All other                            
Segment Reporting Information [Line Items]                            
Total operating revenues                       1,213,000,000 741,000,000 463,000,000
Depreciation and amortization                       66,000,000 52,000,000 31,000,000
Interest income                       8,000,000 11,000,000 20,000,000
Earnings from equity method investments                       2,000,000 (1,000,000) (3,000,000)
Interest expense                       580,000,000 490,000,000 317,000,000
Income taxes                       (222,000,000) (307,000,000) (216,000,000)
Segment net income (loss)                       (453,000,000) (279,000,000) (230,000,000)
Goodwill 298,000,000       299,000,000       282,000,000     298,000,000 299,000,000 282,000,000
Total Assets 3,285,000,000       2,552,000,000       2,474,000,000     3,285,000,000 2,552,000,000 2,474,000,000
Gross property additions                       414,000,000 355,000,000 41,000,000
Intersegment Eliminations                            
Segment Reporting Information [Line Items]                            
Total operating revenues                       (198,000,000) (170,000,000) (160,000,000)
Depreciation and amortization                       0 0 0
Interest income                       (5,000,000) (9,000,000) (15,000,000)
Earnings from equity method investments                       (1,000,000) 0 0
Interest expense                       (1,000,000) (7,000,000) (12,000,000)
Income taxes                       0 0 0
Segment net income (loss)                       3,000,000 0 (7,000,000)
Goodwill 0       0       0     0 0 0
Total Assets (1,778,000,000)       (1,619,000,000)       (1,624,000,000)     (1,778,000,000) (1,619,000,000) (1,624,000,000)
Gross property additions                       0 0 (1,000,000)
Intersegment Eliminations | Electric Utilities                            
Segment Reporting Information [Line Items]                            
Total operating revenues                       (477,000,000) (419,000,000) (439,000,000)
Depreciation and amortization                       0 0 0
Interest income                       0 0 0
Earnings from equity method investments                       0 0 0
Interest expense                       0 0 0
Income taxes                       0 0 0
Segment net income (loss)                       0 0 0
Goodwill       0       0     0 0
Total Assets (306,000,000)       (325,000,000)       (316,000,000)     (306,000,000) (325,000,000) (316,000,000)
Gross property additions                       0 0 0
Southern Power                            
Segment Reporting Information [Line Items]                            
Total operating revenues                       2,205,000,000 2,075,000,000 1,577,000,000
Depreciation and amortization                       493,000,000 503,000,000 352,000,000
Interest expense                       183,000,000 191,000,000 117,000,000
Income taxes 75,000,000                     (164,000,000) (939,000,000) (195,000,000)
Segment net income (loss) (60,000,000) 146,000,000 45,000,000 115,000,000 793,000,000 154,000,000 104,000,000 66,000,000       187,000,000 1,071,000,000 338,000,000
Total Assets 14,883,000,000       15,206,000,000             14,883,000,000 15,206,000,000  
Depreciation and amortization                       524,000,000 536,000,000 370,000,000
Operating Income 30,000,000 136,000,000 16,000,000 60,000,000 32,000,000 159,000,000 112,000,000 65,000,000       242,000,000 368,000,000 290,000,000
Segment and Related Information (Textual) [Abstract]                            
Impairment charges                       156,000,000 0 0
After tax impairment charges                       117,000,000    
Gain (loss) on asset sales                       (2,000,000) 0 0
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)         (743,000,000)                  
Southern Company Gas                            
Segment Reporting Information [Line Items]                            
Total operating revenues                 1,652,000,000     3,909,000,000 3,920,000,000  
Earnings from equity method investments                 60,000,000     148,000,000 106,000,000  
Interest expense                 81,000,000     228,000,000 200,000,000  
Income taxes                 76,000,000     464,000,000 367,000,000  
Segment net income (loss) 78,000,000 46,000,000 (31,000,000) 279,000,000 (60,000,000) 15,000,000 49,000,000 239,000,000 114,000,000     372,000,000 243,000,000  
Goodwill 5,015,000,000       5,967,000,000             5,015,000,000 5,967,000,000  
Total Assets 21,448,000,000       22,987,000,000       21,853,000,000     21,448,000,000 22,987,000,000 21,853,000,000
Gross property additions                 632,000,000     1,521,000,000 1,508,000,000  
Depreciation and amortization                 238,000,000     500,000,000 501,000,000  
Operating Income 104,000,000 $ 374,000,000 $ 49,000,000 388,000,000 109,000,000 $ 67,000,000 $ 95,000,000 $ 389,000,000 199,000,000     915,000,000 660,000,000  
Segment and Related Information (Textual) [Abstract]                            
Gain (loss) on asset sales                 0     291,000,000 0  
Goodwill impairment 0     42,000,000         0     42,000,000 0  
Tax Cuts And Jobs Act Of 2017, income tax expense (benefit)         93,000,000                  
Southern Company Gas | Gas Distribution Operations                            
Segment Reporting Information [Line Items]                            
Goodwill 4,034,000,000       4,702,000,000             4,034,000,000 4,702,000,000  
Segment and Related Information (Textual) [Abstract]                            
Gain (loss) on asset sales                       324,000,000    
Net gain (loss) on dispositions, net of tax                       16,000,000    
Goodwill impairment                       0    
Southern Company Gas | Gas marketing services                            
Segment Reporting Information [Line Items]                            
Goodwill 981,000,000       1,265,000,000             981,000,000 1,265,000,000  
Segment and Related Information (Textual) [Abstract]                            
Gain (loss) on asset sales                       (33,000,000)    
Net gain (loss) on dispositions, net of tax                       (67,000,000)    
Goodwill impairment                       42,000,000    
Southern Company Gas | Intersegment Eliminations                            
Segment Reporting Information [Line Items]                            
Total operating revenues                 (102,000,000)     (76,000,000) (234,000,000)  
Earnings from equity method investments                 0     0 0  
Interest expense                 0     0 0  
Income taxes                 0     0 0  
Segment net income (loss)                 0     0 0  
Total Assets (11,582,000,000)       (14,039,000,000)       (14,167,000,000)     (11,582,000,000) (14,039,000,000) (14,167,000,000)
Gross property additions                 0     0 0  
Depreciation and amortization                 0     0 0  
Operating Income                 0     0 0  
Southern Company Gas | Operating Segments                            
Segment Reporting Information [Line Items]                            
Total operating revenues                 1,723,000,000     3,930,000,000 4,090,000,000  
Earnings from equity method investments                 58,000,000     145,000,000 103,000,000  
Interest expense                 119,000,000     227,000,000 191,000,000  
Income taxes                 76,000,000     495,000,000 311,000,000  
Segment net income (loss)                 125,000,000     435,000,000 358,000,000  
Total Assets 21,918,000,000       24,300,000,000       24,323,000,000     21,918,000,000 24,300,000,000 24,323,000,000
Gross property additions                 618,000,000     1,467,000,000 1,457,000,000  
Depreciation and amortization                 221,000,000     453,000,000 457,000,000  
Operating Income                 251,000,000     1,013,000,000 717,000,000  
Southern Company Gas | Operating Segments | All other                            
Segment Reporting Information [Line Items]                            
Total operating revenues                 31,000,000     55,000,000 64,000,000  
Earnings from equity method investments                 2,000,000     3,000,000 3,000,000  
Interest expense                 (38,000,000)     1,000,000 9,000,000  
Income taxes                 0     (31,000,000) 56,000,000  
Segment net income (loss)                 (11,000,000)     (63,000,000) (115,000,000)  
Total Assets 11,112,000,000       12,726,000,000       11,697,000,000     11,112,000,000 12,726,000,000 11,697,000,000
Gross property additions                 14,000,000     54,000,000 51,000,000  
Depreciation and amortization                 17,000,000     47,000,000 44,000,000  
Operating Income                 (52,000,000)     (98,000,000) (57,000,000)  
Southern Company Gas | Operating Segments | Gas Distribution Operations                            
Segment Reporting Information [Line Items]                            
Total operating revenues                 1,342,000,000     3,186,000,000 3,207,000,000  
Earnings from equity method investments                 0     0 0  
Interest expense                 105,000,000     178,000,000 153,000,000  
Income taxes                 51,000,000     409,000,000 178,000,000  
Segment net income (loss)                 77,000,000     334,000,000 353,000,000  
Total Assets 17,266,000,000       19,358,000,000       19,453,000,000     17,266,000,000 19,358,000,000 19,453,000,000
Gross property additions                 561,000,000     1,429,000,000 1,330,000,000  
Depreciation and amortization                 185,000,000     409,000,000 391,000,000  
Operating Income                 225,000,000     904,000,000 645,000,000  
Segment and Related Information (Textual) [Abstract]                            
Revenue on disposition                 168,000,000     244,000,000 399,000,000  
Southern Company Gas | Operating Segments | Gas Pipeline Investments                            
Segment Reporting Information [Line Items]                            
Total operating revenues                 3,000,000     32,000,000 17,000,000  
Earnings from equity method investments                 58,000,000     145,000,000 103,000,000  
Interest expense                 10,000,000     34,000,000 26,000,000  
Income taxes                 21,000,000     28,000,000 109,000,000  
Segment net income (loss)                 29,000,000     103,000,000 (22,000,000)  
Total Assets 1,763,000,000       1,699,000,000       1,659,000,000     1,763,000,000 1,699,000,000 1,659,000,000
Gross property additions                 51,000,000     32,000,000 117,000,000  
Depreciation and amortization                 0     5,000,000 2,000,000  
Operating Income                 1,000,000     20,000,000 10,000,000  
Southern Company Gas | Operating Segments | Wholesale gas services                            
Segment Reporting Information [Line Items]                            
Total operating revenues                 24,000,000     144,000,000 6,000,000  
Earnings from equity method investments                 0     0 0  
Interest expense                 3,000,000     9,000,000 7,000,000  
Income taxes                 (3,000,000)     4,000,000 0  
Segment net income (loss)                 0     38,000,000 (57,000,000)  
Total Assets 1,302,000,000       1,096,000,000       1,127,000,000     1,302,000,000 1,096,000,000 1,127,000,000
Gross property additions                 1,000,000     0 1,000,000  
Less Gross Gas Costs                 6,116,000,000     7,262,000,000 6,627,000,000  
Depreciation and amortization                 1,000,000     2,000,000 2,000,000  
Operating Income                 (2,000,000)     70,000,000 (51,000,000)  
Southern Company Gas | Operating Segments | Gas marketing services                            
Segment Reporting Information [Line Items]                            
Total operating revenues                 354,000,000     568,000,000 860,000,000  
Earnings from equity method investments                 0     0 0  
Interest expense                 1,000,000     6,000,000 5,000,000  
Income taxes                 7,000,000     54,000,000 24,000,000  
Segment net income (loss)                 19,000,000     (40,000,000) 84,000,000  
Total Assets $ 1,587,000,000       $ 2,147,000,000       2,084,000,000     1,587,000,000 2,147,000,000 $ 2,084,000,000
Gross property additions                 5,000,000     6,000,000 9,000,000  
Depreciation and amortization                 35,000,000     37,000,000 62,000,000  
Operating Income                 27,000,000     19,000,000 113,000,000  
Segment and Related Information (Textual) [Abstract]                            
Revenue on disposition                 56,000,000     55,000,000 129,000,000  
Predecessor | Southern Company Gas                            
Segment Reporting Information [Line Items]                            
Total operating revenues                   $ 1,905,000,000        
Earnings from equity method investments                   2,000,000        
Interest expense                   96,000,000        
Income taxes                   87,000,000        
Segment net income (loss)                   131,000,000        
Gross property additions                   548,000,000        
Depreciation and amortization                   206,000,000        
Operating Income                   323,000,000        
EBIT                   328,000,000        
Segment and Related Information (Textual) [Abstract]                            
Gain (loss) on asset sales                   0        
Goodwill impairment                   0        
Predecessor | Southern Company Gas | Intersegment Eliminations                            
Segment Reporting Information [Line Items]                            
Total operating revenues                   (102,000,000)        
Gross property additions                   0        
Depreciation and amortization                   0        
Operating Income                   0        
EBIT                   0        
Predecessor | Southern Company Gas | Operating Segments                            
Segment Reporting Information [Line Items]                            
Total operating revenues                   1,981,000,000        
Gross property additions                   529,000,000        
Depreciation and amortization                   190,000,000        
Operating Income                   396,000,000        
EBIT                   397,000,000        
Predecessor | Southern Company Gas | Operating Segments | All other                            
Segment Reporting Information [Line Items]                            
Total operating revenues                   26,000,000        
Gross property additions                   19,000,000        
Depreciation and amortization                   16,000,000        
Operating Income                   (73,000,000)        
EBIT                   (69,000,000)        
Predecessor | Southern Company Gas | Operating Segments | Gas Distribution Operations                            
Segment Reporting Information [Line Items]                            
Total operating revenues                   1,575,000,000        
Gross property additions                   484,000,000        
Depreciation and amortization                   178,000,000        
Operating Income                   353,000,000        
EBIT                   353,000,000        
Segment and Related Information (Textual) [Abstract]                            
Revenue on disposition                   215,000,000        
Predecessor | Southern Company Gas | Operating Segments | Gas Pipeline Investments                            
Segment Reporting Information [Line Items]                            
Total operating revenues                   3,000,000        
Gross property additions                   40,000,000        
Depreciation and amortization                   0        
Operating Income                   3,000,000        
EBIT                   3,000,000        
Predecessor | Southern Company Gas | Operating Segments | Wholesale gas services                            
Segment Reporting Information [Line Items]                            
Total operating revenues                   (32,000,000)        
Gross property additions                   1,000,000        
Less Gross Gas Costs                   2,675,000,000        
Depreciation and amortization                   1,000,000        
Operating Income                   (69,000,000)        
EBIT                   (68,000,000)        
Predecessor | Southern Company Gas | Operating Segments | Gas marketing services                            
Segment Reporting Information [Line Items]                            
Total operating revenues                   435,000,000        
Gross property additions                   4,000,000        
Depreciation and amortization                   11,000,000        
Operating Income                   109,000,000        
EBIT                   109,000,000        
Segment and Related Information (Textual) [Abstract]                            
Revenue on disposition                   64,000,000        
Third Party Gross Revenues | Southern Company Gas | Operating Segments | Wholesale gas services                            
Segment Reporting Information [Line Items]                            
Total operating revenues                 5,807,000,000     6,955,000,000 6,152,000,000  
Third Party Gross Revenues | Predecessor | Southern Company Gas | Operating Segments | Wholesale gas services                            
Segment Reporting Information [Line Items]                            
Total operating revenues                   2,500,000,000        
Intercompany Revenues | Southern Company Gas | Operating Segments | Wholesale gas services                            
Segment Reporting Information [Line Items]                            
Total operating revenues                 333,000,000     451,000,000 481,000,000  
Intercompany Revenues | Predecessor | Southern Company Gas | Operating Segments | Wholesale gas services                            
Segment Reporting Information [Line Items]                            
Total operating revenues                   143,000,000        
Total Gross Revenues | Southern Company Gas | Operating Segments | Wholesale gas services                            
Segment Reporting Information [Line Items]                            
Total operating revenues                 $ 6,140,000,000     $ 7,406,000,000 $ 6,633,000,000  
Total Gross Revenues | Predecessor | Southern Company Gas | Operating Segments | Wholesale gas services                            
Segment Reporting Information [Line Items]                            
Total operating revenues                   $ 2,643,000,000        
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas                            
Segment and Related Information (Textual) [Abstract]                            
Number of natural gas distribution utilities disposed | utility 3                     3    
Pivotal Home Solutions | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas                            
Segment and Related Information (Textual) [Abstract]                            
Gain (loss) on asset sales                       $ 291,000,000    
Net gain (loss) on dispositions, net of tax                       (51,000,000)    
Goodwill impairment       $ 42,000,000               $ 42,000,000