ASSET RETIREMENT OBLIGATIONS - Details of AROs Included in the Balance Sheets (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2021	Dec. 31, 2020
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year		$ 10,684	$ 9,786
Liabilities incurred		26	19
Liabilities settled		(456)	(442)
Accretion		407	409
Cash flow revisions		1,026	912
Balance at end of year		11,687	10,684
Alabama Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year		3,974	3,540
Liabilities incurred		0	0
Liabilities settled		(202)	(219)
Accretion		156	152
Cash flow revisions		406	501
Balance at end of year		4,334	3,974
Georgia Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year		6,265	5,784
Liabilities incurred		3	10
Liabilities settled		(210)	(185)
Accretion		236	238
Cash flow revisions	$ 435	530	418
Balance at end of year		6,824	6,265
Mississippi Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year		176	190
Liabilities incurred		0	0
Liabilities settled		(24)	(22)
Accretion		7	8
Cash flow revisions	$ 31	31	0
Balance at end of year		190	176
Southern Power
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year		95	89
Liabilities incurred		23	9
Liabilities settled		0	0
Accretion		5	4
Cash flow revisions		8	(7)
Balance at end of year		$ 131	$ 95