Introduction - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Related Party Transaction [Line Items]
Net income (loss)		$ (127)	$ (1,348)	$ 809	$ (684)
Accretion				95
ALABAMA POWER CO
Related Party Transaction [Line Items]
Net income (loss)		262	235	491	412
Increase in ARO due to new CCR rule	$ 1,200
Accretion				$ 41
Inflation rate assumption				4.50%
Trust earnings rate assumption				7.00%
MISSISSIPPI POWER CO
Related Party Transaction [Line Items]
Net income (loss)		47	(2,053)	$ 40	(2,073)
Increase in ARO due to new CCR rule	11
Accretion				2
GEORGIA POWER CO
Related Party Transaction [Line Items]
Net income (loss)		(396)	352	(44)	616
SOUTHERN Co GAS
Related Party Transaction [Line Items]
Net income (loss)		(31)	49	248	288
Wholesale Gas Services | SOUTHERN Co GAS
Related Party Transaction [Line Items]
Inventory write-down		0	$ 0	0	$ 0
Accounting Standards Update 2014-09 | Effect of Change
Related Party Transaction [Line Items]
Net income (loss)		(5)		5
Accounting Standards Update 2014-09 | Effect of Change | SOUTHERN Co GAS
Related Party Transaction [Line Items]
Net income (loss)		$ (5)		$ 5
Plant Farley | ALABAMA POWER CO
Related Party Transaction [Line Items]
Increase in ARO	$ 300