Revenue from Contracts with Customers and Lease Income - Schedule of Contract Balances (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Accounts Receivable	$ 2,375	$ 2,614
Contract Assets	106	158
Contract Liabilities	75	61
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	567	632
Contract Assets	1	2
Contract Liabilities	4	6
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	679	806
Contract Assets	47	71
Contract Liabilities	34	27
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	87	77
Contract Assets	0	0
Contract Liabilities	1	1
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	85	112
Contract Assets	0	0
Contract Liabilities	1	1
SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Accounts Receivable	778	788
Contract Assets	0	0
Contract Liabilities	$ 1	$ 1