REVENUE FROM CONTRACTS WITH CUSTOMERS AND LEASE INCOME - Narrative (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended
	Aug. 31, 2020	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Contract assets		$ 159	$ 159	$ 117
Contract liabilities		56	56	52
Revenue from contracts with customers recognized		8	29
Unregulated Distributed Generation
Disaggregation of Revenue [Line Items]
Contract assets		47	47	40
Contract liabilities		22	$ 22	28
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Revenue, performance obligation, description of timing			Georgia Power had contract assets primarily related to fixed retail customer bill programs, where the payment is contingent upon Georgia Power's continued performance and the customer's continued participation in the program over a one-year contract term, and unregulated service agreements, where payment is contingent on project completion. Contract liabilities for Georgia Power relate to cash collections recognized in advance of revenue for certain unregulated service agreements. Alabama Power had contract liabilities for outstanding performance obligations primarily related to extended service agreements.
Contract assets		103	$ 103	69
Contract liabilities		24	24	13
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Contract assets		5	5	0
Contract liabilities		1	1	10
ALABAMA POWER CO | Autauga Combined Cycle
Disaggregation of Revenue [Line Items]
Power sales agreement, remaining term	3 years
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Contract assets		0	0	0
Contract liabilities		0	0	$ 0
Sales-type lease, lease receivable		25	25
Transfer of construction work in progress to lease receivables		25
MISSISSIPPI POWER CO | Other Property and Investments
Disaggregation of Revenue [Line Items]
Sales-type lease, lease receivable		22	22
MISSISSIPPI POWER CO | Other Accounts Notes and Loans Receivable
Disaggregation of Revenue [Line Items]
Sales-type lease, lease receivable		$ 3	$ 3