SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Storm Damage Reserves (Details) - Major storms - USD ($)		1 Months Ended	12 Months Ended
	Dec. 03, 2019	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Liability for Catastrophe Claims [Line Items]
Storm damage reserves			$ 170,000,000	$ 74,000,000	$ 41,000,000
Alabama Power
Liability for Catastrophe Claims [Line Items]
Additional accruals authorized by state PSCs			84,000,000	0	0
Storm damage reserves		$ 84,000,000	139,000,000	16,000,000	4,000,000
Georgia Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves			30,000,000	30,000,000	30,000,000
Mississippi Power
Liability for Catastrophe Claims [Line Items]
Additional accruals authorized by state PSCs			0	0	0
Storm damage reserves			$ 1,000,000	1,000,000	3,000,000
Gulf Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves				$ 26,900,000	$ 3,500,000
Accumulated Deferred Income Taxes | Alabama Power
Liability for Catastrophe Claims [Line Items]
Storm damage reserves	$ 39,000,000