REVENUE FROM CONTRACTS WITH CUSTOMERS AND LEASE INCOME - Contract Balances (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Accounts Receivables	$ 2,283	$ 2,413
Contract Assets	103	117
Contract Liabilities	57	52
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivables	592	586
Contract Assets	0	0
Contract Liabilities	6	10
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivables	796	688
Contract Assets	54	69
Contract Liabilities	23	13
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivables	84	79
Contract Assets	1	0
Contract Liabilities	0	0
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivables	115	97
Contract Assets	0	0
Contract Liabilities	1	1
SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Accounts Receivables	523	749
Contract Assets	0	0
Contract Liabilities	$ 2	$ 1