Retirement Benefits (Details) - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected future employer contributions, remainder of fiscal year	$ 0
Pension Plans and Postretirement Plans
Service cost	103,000,000	$ 109,000,000
Interest cost	102,000,000	87,000,000
Expected return on plan assets	(316,000,000)	(298,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	60,000,000	78,000,000
Net periodic pension cost (income)	(51,000,000)	(24,000,000)
Pension Plans | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	25,000,000	26,000,000
Interest cost	24,000,000	20,000,000
Expected return on plan assets	(77,000,000)	(72,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	16,000,000	21,000,000
Net periodic pension cost (income)	(12,000,000)	(5,000,000)
Pension Plans | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	26,000,000	28,000,000
Interest cost	31,000,000	26,000,000
Expected return on plan assets	(99,000,000)	(94,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	18,000,000	25,000,000
Net periodic pension cost (income)	(24,000,000)	(15,000,000)
Pension Plans | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	4,000,000	4,000,000
Interest cost	5,000,000	4,000,000
Expected return on plan assets	(15,000,000)	(14,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	3,000,000	4,000,000
Net periodic pension cost (income)	(3,000,000)	(2,000,000)
Pension Plans | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	2,000,000
Interest cost	2,000,000	1,000,000
Expected return on plan assets	(4,000,000)	(3,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	1,000,000	1,000,000
Net periodic pension cost (income)	1,000,000	1,000,000
Pension Plans | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	9,000,000	9,000,000
Interest cost	7,000,000	6,000,000
Expected return on plan assets	(22,000,000)	(21,000,000)
Amortization:
Prior service costs	(1,000,000)	(1,000,000)
Regulatory asset	4,000,000	4,000,000
Net (gain)/loss	2,000,000	3,000,000
Net periodic pension cost (income)	(1,000,000)	0
Postretirement Benefits
Pension Plans and Postretirement Plans
Service cost	6,000,000	6,000,000
Interest cost	10,000,000	8,000,000
Expected return on plan assets	(20,000,000)	(19,000,000)
Amortization:
Regulatory asset	0	0
Net (gain)/loss		1,000,000
Net periodic pension cost (income)	(4,000,000)	(4,000,000)
Postretirement Benefits | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000
Interest cost	3,000,000	2,000,000
Expected return on plan assets	(8,000,000)	(7,000,000)
Amortization:
Regulatory asset	0	0
Net (gain)/loss		0
Net periodic pension cost (income)	(4,000,000)	(4,000,000)
Postretirement Benefits | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	2,000,000
Interest cost	4,000,000	3,000,000
Expected return on plan assets	(7,000,000)	(7,000,000)
Amortization:
Regulatory asset	0	0
Net (gain)/loss		1,000,000
Net periodic pension cost (income)	(1,000,000)	(1,000,000)
Postretirement Benefits | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	0	0
Interest cost	0	0
Expected return on plan assets	0	0
Amortization:
Regulatory asset	0	0
Net (gain)/loss		0
Net periodic pension cost (income)	0	0
Postretirement Benefits | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	0	0
Interest cost	0	0
Expected return on plan assets	0	0
Amortization:
Regulatory asset	0	0
Net (gain)/loss		0
Net periodic pension cost (income)	0	0
Postretirement Benefits | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	0	0
Interest cost	1,000,000	1,000,000
Expected return on plan assets	(2,000,000)	(2,000,000)
Amortization:
Regulatory asset	2,000,000	2,000,000
Net (gain)/loss		(1,000,000)
Net periodic pension cost (income)	$ 1,000,000	$ 0