v3.10.0.1
Asset Retirement Obligations - Details of AROs Included in the Balance Sheets (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Balance at beginning of year $ 4,824 $ 4,514
Liabilities incurred 29 16
Liabilities settled (244) (177)
Accretion 217 179
Cash flow revisions 4,737 292
Reclassification to held for sale (169)  
Balance at end of year 9,394 4,824
Alabama Power    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Balance at beginning of year 1,709 1,533
Liabilities incurred 0 0
Liabilities settled (55) (26)
Accretion 106 77
Cash flow revisions 1,450 125
Reclassification to held for sale 0  
Balance at end of year 3,210 1,709
Georgia Power    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Balance at beginning of year 2,638 2,532
Liabilities incurred 27 4
Liabilities settled (116) (120)
Accretion 94 89
Cash flow revisions 3,186 133
Reclassification to held for sale 0  
Balance at end of year 5,829 2,638
Mississippi Power    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Balance at beginning of year 174 179
Liabilities incurred 0 0
Liabilities settled (35) (23)
Accretion 5 5
Cash flow revisions 16 13
Reclassification to held for sale 0  
Balance at end of year 160 174
Southern Power    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Balance at beginning of year 78 64
Liabilities incurred 2 6
Liabilities settled 0 0
Accretion 4 4
Cash flow revisions 0 4
Reclassification to held for sale 0  
Balance at end of year $ 84 $ 78