v3.10.0.1
Summary of Significant Accounting Policies - Schedule of Other Intangible Assets (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount $ 773 $ 984
Accumulated Amortization (235) (186)
Other Intangible Assets, Net 538 798
Intangible assets, gross 848 1,059
Intangible assets, net 613 873
Federal Communications Commission licenses    
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount 75 75
Accumulated Amortization 0 0
Other Intangible Assets, Net 75 75
Customer relationships    
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount 223 288
Accumulated Amortization (94) (83)
Other Intangible Assets, Net 129 205
Trade names    
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount 70 159
Accumulated Amortization (21) (17)
Other Intangible Assets, Net 49 142
Storage and transportation contracts    
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount 64 64
Accumulated Amortization (54) (34)
Other Intangible Assets, Net 10 30
PPA fair value adjustments(b)    
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount 405 456
Accumulated Amortization (61) (47)
Other Intangible Assets, Net 344 409
Other    
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount 11 17
Accumulated Amortization (5) (5)
Other Intangible Assets, Net 6 12
Southern Power    
Finite-Lived Intangible Assets [Line Items]    
Accumulated Amortization (61) (47)
Southern Power | PPA fair value adjustments(b)    
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount 405 456
Accumulated Amortization (61) (47)
Other Intangible Assets, Net 344 409
Southern Company Gas    
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount 246 400
Accumulated Amortization (145) (120)
Other Intangible Assets, Net 101 280
Intangible assets, net 101 280
Southern Company Gas | Customer relationships    
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount 156 221
Accumulated Amortization (84) (77)
Other Intangible Assets, Net 72 144
Southern Company Gas | Trade names    
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount 26 115
Accumulated Amortization (7) (9)
Other Intangible Assets, Net 19 106
Southern Company Gas | Storage and transportation contracts    
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount 64 64
Accumulated Amortization (54) (34)
Other Intangible Assets, Net $ 10 $ 30