REVENUE FROM CONTRACTS WITH CUSTOMERS AND LEASE INCOME - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Contract assets	$ 103	$ 103	$ 117
Contract liabilities	57	57	52
Revenue from contracts with customers recognized	11	21
Unregulated Distributed Generation
Disaggregation of Revenue [Line Items]
Contract assets	41	41	40
Contract liabilities	26	$ 26	28
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Revenue, performance obligation, description of timing		Georgia Power had contract assets primarily related to unregulated service agreements, where payment is contingent on project completion, and 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. 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	54	$ 54	69
Contract liabilities	$ 23	$ 23	$ 13