Contingencies - Other Matters (Details) - USD ($) $ in Millions			1 Months Ended		9 Months Ended
	Oct. 05, 2023	Oct. 03, 2023	Aug. 31, 2022	Apr. 30, 2019	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2019	Dec. 31, 2022	Dec. 31, 2017	Dec. 31, 2011
Loss Contingencies [Line Items]
Associated penalties and interest previously paid					$ (67)	$ (119)
Penalties and interest final payment					(1,031)	805
Regulatory asset					16			$ 216
ALABAMA POWER CO
Loss Contingencies [Line Items]
Associated penalties and interest previously paid					(21)	(98)
Penalties and interest final payment					(358)	(22)
Regulatory asset					71			97
ALABAMA POWER CO | AT&T
Loss Contingencies [Line Items]
Potential refund amount owed				$ 87
Refund payment period				6 years
MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Total amount due including penalties and interest			$ 28
Associated penalties and interest previously paid			$ 7		12	36
Penalties and interest final payment					(83)	$ 41
Regulatory asset					$ 42			36
MISSISSIPPI POWER CO | Kemper IGCC
Loss Contingencies [Line Items]
DOE awards									$ 137	$ 270
Government grants received							$ 387
MISSISSIPPI POWER CO | Taxes and Interest
Loss Contingencies [Line Items]
Regulatory asset								$ 3
MISSISSIPPI POWER CO | Subsequent Event
Loss Contingencies [Line Items]
Assessment including penalties and interest		$ 11
Penalties and interest final payment	$ 4