Financing - Bank Credit Arrangements Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 19, 2019	Dec. 31, 2017
Debt Disclosure [Line Items]
Ratio of indebtedness to capitalization, debt covenant, required	70.00%
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	$ 1,600,000,000
Remarketed pollution control bonds	403,000,000
Line of credit facility, maximum borrowing capacity	7,863,000,000
Unused credit with banks	$ 7,820,000,000
Other Subsidiaries
Debt Disclosure [Line Items]
Ratio of indebtedness to capitalization, debt covenant, required	65.00%
Line of credit facility, maximum borrowing capacity	$ 30,000,000
Unused credit with banks	30,000,000
Alabama Power
Debt Disclosure [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	854,000,000
Line of credit facility, maximum borrowing capacity	1,333,000,000
Unused credit with banks	1,333,000,000
Georgia Power
Debt Disclosure [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	659,000,000
Remarketed pollution control bonds	345,000,000
Line of credit facility, maximum borrowing capacity	1,750,000,000
Unused credit with banks	1,736,000,000
Georgia Power | Municipal bonds | Subsequent Event
Debt Disclosure [Line Items]
Debt instrument, repurchased face amount		$ 108,000,000
Gulf Power
Debt Disclosure [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	82,000,000
Remarketed pollution control bonds	58,000,000
Line of credit facility, maximum borrowing capacity	280,000,000
Mississippi Power
Debt Disclosure [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	40,000,000
Line of credit facility, maximum borrowing capacity	100,000,000
Unused credit with banks	100,000,000
Southern Power
Debt Disclosure [Line Items]
Line of credit facility, maximum borrowing capacity	750,000,000
Unused credit with banks	727,000,000
Southern Power | Continuing Letter of Credit Facility
Debt Disclosure [Line Items]
Line of credit facility, maximum borrowing capacity	120,000,000
Unused credit with banks	103,000,000		$ 19,000,000
Southern Power | Power Purchase Agreement
Debt Disclosure [Line Items]
Unused credit with banks	17,000,000
Debt instrument, collateral amount	$ 103,000,000		$ 113,000,000