Retirement Benefits (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected future employer contributions, remainder of fiscal year	$ 0		$ 0
Pension Plans and Postretirement Plans
Service cost	108,000,000	$ 94,000,000	217,000,000	$ 188,000,000
Interest cost	86,000,000	108,000,000	173,000,000	216,000,000
Expected return on plan assets	(297,000,000)	(275,000,000)	(595,000,000)	(550,000,000)
Amortization:
Prior service costs	0	0	0	1,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	79,000,000	67,000,000	157,000,000	134,000,000
Net periodic pension cost (income)	(24,000,000)	(6,000,000)	(48,000,000)	(11,000,000)
Pension Plans | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	25,000,000	22,000,000	51,000,000	44,000,000
Interest cost	21,000,000	25,000,000	41,000,000	50,000,000
Expected return on plan assets	(71,000,000)	(66,000,000)	(143,000,000)	(132,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	20,000,000	18,000,000	41,000,000	36,000,000
Net periodic pension cost (income)	(5,000,000)	(1,000,000)	(10,000,000)	(2,000,000)
Pension Plans | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	28,000,000	24,000,000	56,000,000	48,000,000
Interest cost	26,000,000	34,000,000	52,000,000	67,000,000
Expected return on plan assets	(94,000,000)	(87,000,000)	(188,000,000)	(174,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000	1,000,000	1,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	25,000,000	21,000,000	50,000,000	43,000,000
Net periodic pension cost (income)	(14,000,000)	(7,000,000)	(29,000,000)	(15,000,000)
Pension Plans | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	5,000,000	4,000,000	9,000,000	8,000,000
Interest cost	4,000,000	5,000,000	8,000,000	10,000,000
Expected return on plan assets	(13,000,000)	(12,000,000)	(27,000,000)	(25,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	3,000,000	3,000,000	7,000,000	6,000,000
Net periodic pension cost (income)	(1,000,000)	0	(3,000,000)	(1,000,000)
Pension Plans | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	3,000,000	2,000,000	5,000,000	4,000,000
Interest cost	1,000,000	2,000,000	2,000,000	3,000,000
Expected return on plan assets	(4,000,000)	(3,000,000)	(7,000,000)	(6,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	1,000,000	0	2,000,000	1,000,000
Net periodic pension cost (income)	1,000,000	1,000,000	2,000,000	2,000,000
Pension Plans | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	9,000,000	8,000,000	18,000,000	16,000,000
Interest cost	6,000,000	7,000,000	12,000,000	15,000,000
Expected return on plan assets	(22,000,000)	(20,000,000)	(43,000,000)	(39,000,000)
Amortization:
Prior service costs	0	0	(1,000,000)	(1,000,000)
Regulatory asset	4,000,000	4,000,000	8,000,000	8,000,000
Net (gain)/loss	3,000,000	3,000,000	6,000,000	5,000,000
Net periodic pension cost (income)	0	2,000,000	0	4,000,000
Postretirement Benefits
Pension Plans and Postretirement Plans
Service cost	6,000,000	6,000,000	12,000,000	11,000,000
Interest cost	9,000,000	14,000,000	17,000,000	27,000,000
Expected return on plan assets	(19,000,000)	(18,000,000)	(38,000,000)	(36,000,000)
Amortization:
Prior service costs	(1,000,000)	(1,000,000)	(1,000,000)	(1,000,000)
Regulatory asset	0	0	0	0
Net (gain)/loss	1,000,000	0	2,000,000	1,000,000
Net periodic pension cost (income)	(4,000,000)	1,000,000	(8,000,000)	2,000,000
Postretirement Benefits | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	1,000,000	3,000,000	3,000,000
Interest cost	2,000,000	3,000,000	4,000,000	6,000,000
Expected return on plan assets	(7,000,000)	(7,000,000)	(14,000,000)	(14,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	0	0
Net periodic pension cost (income)	(3,000,000)	(3,000,000)	(7,000,000)	(5,000,000)
Postretirement Benefits | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	2,000,000	3,000,000	3,000,000
Interest cost	3,000,000	5,000,000	6,000,000	10,000,000
Expected return on plan assets	(6,000,000)	(6,000,000)	(13,000,000)	(13,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	1,000,000	1,000,000
Net periodic pension cost (income)	(2,000,000)	1,000,000	(3,000,000)	1,000,000
Postretirement Benefits | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	0	1,000,000	0	1,000,000
Interest cost	1,000,000	1,000,000	1,000,000	1,000,000
Expected return on plan assets	(1,000,000)	(1,000,000)	(1,000,000)	(1,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	0	0
Net periodic pension cost (income)	0	1,000,000	0	1,000,000
Postretirement Benefits | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	0	0	0	0
Interest cost	0	0	0	0
Expected return on plan assets	0	0	0	0
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	0	0
Net periodic pension cost (income)	0	0	0	0
Postretirement Benefits | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000	1,000,000	1,000,000
Interest cost	1,000,000	4,000,000	2,000,000	6,000,000
Expected return on plan assets	(2,000,000)	(2,000,000)	(4,000,000)	(4,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	1,000,000	1,000,000	3,000,000	3,000,000
Net (gain)/loss	0	(1,000,000)	(1,000,000)	(2,000,000)
Net periodic pension cost (income)	$ 1,000,000	$ 3,000,000	$ 1,000,000	$ 4,000,000