Revenue from Contracts with Customers - Contract Balances (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 2,785
Contract Assets	33
Contract Liabilities	36
ALABAMA POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	603
Contract Assets	0
Contract Liabilities	10
GEORGIA POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	840
Contract Assets	9
Contract Liabilities	$ 9
Performance obligation, expected timing of satisfaction	1 year
GULF POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 169
Contract Assets	0
Contract Liabilities	1
MISSISSIPPI POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	83
Contract Assets	0
Contract Liabilities	0
SOUTHERN POWER CO
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	136
Contract Assets	0
Contract Liabilities	4
SOUTHERN Co GAS
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	570
Contract Assets	0
Contract Liabilities	1
Unregulated Distributed Generation
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract Assets	23
Contract Liabilities	$ 16