Derivatives - Schedule of Interest Rate Derivatives (Details) - Interest rate derivatives $ in Millions	9 Months Ended
	Sep. 30, 2023 USD ($)
Derivative [Line Items]
Notional Amount	$ 1,900
Fair Value Gain (Loss)	(351)
Southern Company parent | Fair Value Hedges of Existing Debt | March 2028
Derivative [Line Items]
Notional Amount	$ 400
Interest Rate Received	1.75%
Fair Value Gain (Loss)	$ (56)
Southern Company parent | Fair Value Hedges of Existing Debt | April 2030
Derivative [Line Items]
Notional Amount	$ 1,000
Interest Rate Received	3.70%
Fair Value Gain (Loss)	$ (196)
SOUTHERN Co GAS | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Fair Value Gain (Loss)	(99)
SOUTHERN Co GAS | Fair Value Hedges of Existing Debt | January 2031
Derivative [Line Items]
Notional Amount	$ 500
Interest Rate Received	1.75%
Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | Southern Company parent | Fair Value Hedges of Existing Debt | March 2028
Derivative [Line Items]
Weighted Average Interest Rate Paid	0.80%
Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | Southern Company parent | Fair Value Hedges of Existing Debt | April 2030
Derivative [Line Items]
Weighted Average Interest Rate Paid	2.48%
Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | SOUTHERN Co GAS | Fair Value Hedges of Existing Debt | January 2031
Derivative [Line Items]
Weighted Average Interest Rate Paid	0.49%