DERIVATIVES - Interest Rate Derivatives (Details) - Interest rate derivatives $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Derivative [Line Items]
Notional Amount	$ 2,500
Fair Value Gain (Loss) December 31, 2019	(22)
Georgia Power | Maturity Date March 2025 | Cash Flow Hedges Of Forecasted Debt
Derivative [Line Items]
Notional Amount	$ 250
Weighted Average Interest Rate Paid	2.23%
Fair Value Gain (Loss) December 31, 2019	$ (6)
Georgia Power | Maturity Date March 2030 | Cash Flow Hedges Of Forecasted Debt
Derivative [Line Items]
Notional Amount	$ 250
Weighted Average Interest Rate Paid	2.40%
Fair Value Gain (Loss) December 31, 2019	$ (11)
Southern Company Gas | Maturity Date September 2030 | Cash Flow Hedges Of Forecasted Debt
Derivative [Line Items]
Notional Amount	$ 200
Weighted Average Interest Rate Paid	1.81%
Fair Value Gain (Loss) December 31, 2019	$ 2
Southern Company | Maturity Date June 2020 | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 300
Weighted Average Interest Rate Paid	0.92%
Fair Value Gain (Loss) December 31, 2019	$ 0
Interest Rate Received	2.75%
Southern Company | Maturity Date June 2021 | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 1,500
Weighted Average Interest Rate Paid	0.87%
Fair Value Gain (Loss) December 31, 2019	$ (7)
Interest Rate Received	2.35%