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Introduction - Intangibles, Amortization (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2017
Finite-Lived Intangible Assets [Line Items]    
Amortization of intangible assets $ 29 $ 65
SOUTHERN POWER CO    
Finite-Lived Intangible Assets [Line Items]    
Amortization of intangible assets 6 13
SOUTHERN Co GAS    
Finite-Lived Intangible Assets [Line Items]    
Amortization of intangible assets $ 20 $ 46