Revenue from Contracts with Customers - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Contract assets	$ 84	$ 102
Contract liabilities	62	32
Unregulated Distributed Generation
Disaggregation of Revenue [Line Items]
Contract assets	34	39
Contract liabilities	$ 25	11
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Performance obligation, expected timing of satisfaction	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 the one-year contract term.
Contract assets	$ 41	58
Contract liabilities	$ 25	$ 7