FINANCING - Notes Payable (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Amount Outstanding	$ 2,055	$ 2,915
Weighted Average Interest Rate	2.10%	3.10%
Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 1,705	$ 1,064
Weighted Average Interest Rate	2.10%	3.00%
Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 350	$ 1,851
Weighted Average Interest Rate	2.30%	3.10%
Georgia Power
Short-term Debt [Line Items]
Amount Outstanding	$ 365	$ 294
Weighted Average Interest Rate	2.20%	3.10%
Georgia Power | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 115	$ 294
Weighted Average Interest Rate	2.10%	3.10%
Georgia Power | Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 250	$ 0
Weighted Average Interest Rate	2.20%	0.00%
Southern Power
Short-term Debt [Line Items]
Amount Outstanding	$ 549	$ 100
Weighted Average Interest Rate	2.20%	3.10%
Southern Power | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 449	$ 0
Weighted Average Interest Rate	2.10%	0.00%
Southern Power | Short-term bank debt
Short-term Debt [Line Items]
Amount Outstanding	$ 100	$ 100
Weighted Average Interest Rate	2.60%	3.10%
Southern Company Gas
Short-term Debt [Line Items]
Amount Outstanding	$ 650	$ 650
Southern Company Gas | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 650	$ 650
Weighted Average Interest Rate	2.00%	3.00%
Southern Company Gas Capital | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 372	$ 403
Weighted Average Interest Rate	2.10%	3.10%
Nicor Gas | Commercial Paper
Short-term Debt [Line Items]
Amount Outstanding	$ 278	$ 247
Weighted Average Interest Rate	1.80%	3.00%