Revenue from Contracts with Customers - Contract Balances (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 2,630
Contract Assets	102
Contract Liabilities	32
Unregulated Distributed Generation
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract Assets	39
Contract Liabilities	11
Alabama Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	520
Contract Assets	0
Contract Liabilities	12
Georgia Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	721
Contract Assets	58
Contract Liabilities	$ 7
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 and to unregulated service agreements where payment is contingent upon project completion. Georgia Power also had contract liabilities for outstanding performance obligations primarily related to unregulated service agreements.
Mississippi Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 100
Contract Assets	0
Contract Liabilities	0
Southern Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	118
Contract Assets	0
Contract Liabilities	11
Southern Company Gas
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	952
Contract Assets	0
Contract Liabilities	$ 2