Revenue from Contracts with Customers and Lease Income - Schedule of Contract Balances (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Accounts Receivable	$ 2,271	$ 2,614
Contract Assets	98	158
Contract Liabilities	67	61
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	633	632
Contract Assets	0	2
Contract Liabilities	5	6
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	887	806
Contract Assets	36	71
Contract Liabilities	37	27
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	85	77
Contract Assets	0	0
Contract Liabilities	1	1
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	129	112
Contract Assets	1	0
Contract Liabilities	1	1
SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Accounts Receivable	368	788
Contract Assets	0	0
Contract Liabilities	$ 0	$ 1