Derivatives - Interest Rate Derivatives (Details) - Interest rate derivatives $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Derivative [Line Items]
Notional Amount	$ 2,000
Fair value gain (loss) at December 31, 2018	(49)
Southern Company | Maturity Date June 2020 | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 300
Interest Rate Received	2.75%
Weighted Average Interest Rate Paid	0.92%
Fair value gain (loss) at December 31, 2018	$ (4)
Southern Company | Maturity Date June 2021 | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 1,500
Interest Rate Received	2.35%
Weighted Average Interest Rate Paid	0.87%
Fair value gain (loss) at December 31, 2018	$ (43)
Georgia Power | Maturity Date December 2019 | Fair Value Hedges of Existing Debt
Derivative [Line Items]
Notional Amount	$ 200
Interest Rate Received	4.25%
Weighted Average Interest Rate Paid	2.46%
Fair value gain (loss) at December 31, 2018	$ (2)