FINANCING - Notes Payable (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Short-term Debt [Line Items]
Amount Outstanding	$ 1,440	$ 609
Weighted Average Interest Rate	0.40%	0.30%
Commercial paper
Short-term Debt [Line Items]
Amount Outstanding	$ 1,140	$ 609
Weighted Average Interest Rate	0.30%	0.30%
Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 300	$ 0
Weighted Average Interest Rate	0.70%	0.00%
Georgia Power
Short-term Debt [Line Items]
Amount Outstanding	$ 0	$ 60
Georgia Power | Commercial paper
Short-term Debt [Line Items]
Amount Outstanding	$ 0	$ 60
Weighted Average Interest Rate	0.00%	0.30%
Mississippi Power
Short-term Debt [Line Items]
Amount Outstanding	$ 0	$ 25
Mississippi Power | Commercial paper
Short-term Debt [Line Items]
Amount Outstanding	$ 0	$ 25
Weighted Average Interest Rate	0.00%	0.40%
Southern Power
Short-term Debt [Line Items]
Amount Outstanding	$ 211	$ 175
Southern Power | Commercial paper
Short-term Debt [Line Items]
Amount Outstanding	$ 211	$ 175
Weighted Average Interest Rate	0.30%	0.30%
Southern Company Gas
Short-term Debt [Line Items]
Amount Outstanding	$ 1,209	$ 324
Southern Company Gas | Commercial paper
Short-term Debt [Line Items]
Amount Outstanding	$ 1,209	$ 324
Weighted Average Interest Rate	0.40%	0.20%
Southern Company Gas Capital | Commercial paper
Short-term Debt [Line Items]
Amount Outstanding	$ 379	$ 220
Weighted Average Interest Rate	0.30%	0.30%
Nicor Gas | Commercial paper
Short-term Debt [Line Items]
Amount Outstanding	$ 530	$ 104
Weighted Average Interest Rate	0.30%	0.20%
Nicor Gas | Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 300	$ 0
Weighted Average Interest Rate	0.70%	0.00%