Revenue from Contracts with Customers - Contract Balances (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 2,778
Contract Assets	99
Contract Liabilities	34
Unregulated Distributed Generation
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract Assets	27
Contract Liabilities	17
ALABAMA POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	649
Contract Assets	1
Contract Liabilities	14
GEORGIA POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	924
Contract Assets	70
Contract Liabilities	$ 3
Performance obligation, expected timing of satisfaction	Georgia Power had contract assets primarily related to fixed retail customer bill programs where the payment is contingent upon Georgia Power's continued performance and the customer's continued participation in the program over the one-year contract term.
GULF POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 186
Contract Assets	0
Contract Liabilities	0
MISSISSIPPI POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	96
Contract Assets	0
Contract Liabilities	0
SOUTHERN POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	142
Contract Assets	0
Contract Liabilities	17
SOUTHERN Co GAS
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	523
Contract Assets	0
Contract Liabilities	$ 1