Derivatives - Schedule of Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - Long-term debt - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Derivative [Line Items]
Carrying Amount of the Hedged Item	$ (3,136)	$ (3,280)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	126	9
SOUTHERN Co GAS
Derivative [Line Items]
Carrying Amount of the Hedged Item	(459)	(493)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	$ 37	$ 2