Revenue from Contracts with Customers and Lease Income - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Contract assets	$ 98	$ 98	$ 158
Contract liabilities	67	67	61
Revenue from contracts with customers recognized	12	21
Unregulated Distributed Generation
Disaggregation of Revenue [Line Items]
Contract assets	60	60	81
Contract liabilities	24	24	27
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Contract assets	36	36	71
Contract liabilities	37	37	27
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Contract assets	0	0	0
Contract liabilities	1	1	$ 1
Sales-type lease, lease receivable	35	$ 35
Transfer of construction work in progress to lease receivables	$ 35