v3.10.0.1
Consolidated Entities and Equity Method Investments - Balance Sheet Information (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]    
Equity investments in unconsolidated subsidiaries $ 1,580 $ 1,513
Southern Company Gas    
Schedule of Equity Method Investments [Line Items]    
Equity investments in unconsolidated subsidiaries 1,538 1,477
SNG | Southern Company Gas    
Schedule of Equity Method Investments [Line Items]    
Equity investments in unconsolidated subsidiaries 1,261 1,262
Current assets 104 82
Property, plant, and equipment 2,606 2,439
Deferred charges and other assets 121 121
Total Assets 2,831 2,642
Current liabilities 103 110
Long-term debt 1,103 1,102
Other deferred charges and other liabilities 212 76
Total Liabilities 1,418 1,288
Total Stockholders' Equity 1,413 1,354
Total Liabilities and Stockholders' Equity 2,831 2,642
PennEast Pipeline | Southern Company Gas    
Schedule of Equity Method Investments [Line Items]    
Equity investments in unconsolidated subsidiaries 71 57
Atlantic Coast Pipeline | Southern Company Gas    
Schedule of Equity Method Investments [Line Items]    
Equity investments in unconsolidated subsidiaries 83 41
Other | Southern Company Gas    
Schedule of Equity Method Investments [Line Items]    
Equity investments in unconsolidated subsidiaries $ 123 $ 117