REVENUE FROM CONTRACTS WITH CUSTOMERS - Contract Balances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivable	$ 2,504	$ 2,614
Contract Assets	117	158
Contract Liabilities	57	61
Contract with customer, liability, revenue recognized	29	33
Unregulated Distributed Generation
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract Assets	50	81
Contract Liabilities	39	27
Alabama Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivable	589	632
Contract Assets	2	2
Contract Liabilities	4	6
Georgia Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivable	736	806
Contract Assets	63	71
Contract Liabilities	14	27
Mississippi Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivable	73	77
Contract Assets	0	0
Contract Liabilities	0	1
Southern Power
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivable	149	112
Contract Assets	1	0
Contract Liabilities	1	1
Southern Company Gas
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivable	753	788
Contract Assets	0	0
Contract Liabilities	$ 0	$ 1