Revenue from Contracts with Customers - Contract Balances (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 2,607
Contract Assets	60
Contract Liabilities	52
ALABAMA POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	507
Contract Assets	0
Contract Liabilities	11
GEORGIA POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	600
Contract Assets	29
Contract Liabilities	$ 5
Performance obligation, expected timing of satisfaction	1 year
GULF POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 129
Contract Assets	0
Contract Liabilities	1
MISSISSIPPI POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	64
Contract Assets	0
Contract Liabilities	0
SOUTHERN POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	78
Contract Assets	0
Contract Liabilities	4
SOUTHERN Co GAS
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	948
Contract Assets	0
Contract Liabilities	15
Unregulated Distributed Generation [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract Assets	31
Contract Liabilities	$ 20