ASSET RETIREMENT OBLIGATIONS - Fair Value Increases (Decreases) of the Funds (Details) - Securities held in the Funds - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fair value increases
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	$ 274	$ 280	$ 344
Unrealized gains (losses)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	(27)	220	259
Alabama Power | Fair value increases
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	200	142	194
Alabama Power | Unrealized gains (losses)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	(30)	121	149
Georgia Power | Fair value increases
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	74	138	150
Georgia Power | Unrealized gains (losses)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
Fair value increases (decreases) of the Funds	$ 3	$ 99	$ 110