Retirement Benefits (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Amortization:
Net (gain)/loss
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	73,000,000	90,000,000	219,000,000	$ 269,000,000
Interest cost	123,000,000	116,000,000	369,000,000	348,000,000
Expected return on plan assets	(222,000,000)	(236,000,000)	(664,000,000)	(707,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000	2,000,000	3,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	30,000,000	53,000,000	90,000,000	160,000,000
Net periodic pension cost (income)	5,000,000	24,000,000	16,000,000	73,000,000
Pension Plans | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	17,000,000	19,000,000	51,000,000	58,000,000
Interest cost	28,000,000	26,000,000	85,000,000	76,000,000
Expected return on plan assets	(51,000,000)	(51,000,000)	(154,000,000)	(155,000,000)
Amortization:
Prior service costs	0	0	1,000,000	1,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	9,000,000	13,000,000	27,000,000	40,000,000
Net periodic pension cost (income)	3,000,000	7,000,000	10,000,000	20,000,000
Pension Plans | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	19,000,000	22,000,000	56,000,000	65,000,000
Interest cost	38,000,000	34,000,000	116,000,000	104,000,000
Expected return on plan assets	(73,000,000)	(74,000,000)	(219,000,000)	(222,000,000)
Amortization:
Prior service costs	0	1,000,000	1,000,000	2,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	11,000,000	18,000,000	33,000,000	52,000,000
Net periodic pension cost (income)	(5,000,000)	1,000,000	(13,000,000)	1,000,000
Pension Plans | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	3,000,000	5,000,000	9,000,000	13,000,000
Interest cost	6,000,000	5,000,000	17,000,000	15,000,000
Expected return on plan assets	(10,000,000)	(11,000,000)	(30,000,000)	(31,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	1,000,000	3,000,000	4,000,000	8,000,000
Net periodic pension cost (income)	0	2,000,000	0	5,000,000
Pension Plans | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	3,000,000	5,000,000	7,000,000
Interest cost	1,000,000	1,000,000	4,000,000	4,000,000
Expected return on plan assets	(2,000,000)	(3,000,000)	(7,000,000)	(8,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	0	1,000,000
Net periodic pension cost (income)	1,000,000	1,000,000	2,000,000	4,000,000
Pension Plans | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	7,000,000	8,000,000	19,000,000	24,000,000
Interest cost	9,000,000	10,000,000	27,000,000	29,000,000
Expected return on plan assets	(15,000,000)	(18,000,000)	(45,000,000)	(53,000,000)
Amortization:
Prior service costs	(1,000,000)	(1,000,000)	(2,000,000)	(2,000,000)
Regulatory asset	3,000,000	4,000,000	10,000,000	11,000,000
Net (gain)/loss	1,000,000	3,000,000	2,000,000	9,000,000
Net periodic pension cost (income)	4,000,000	6,000,000	11,000,000	18,000,000
Postretirement Benefits
Pension Plans and Postretirement Plans
Service cost	5,000,000	6,000,000	14,000,000	18,000,000
Interest cost	18,000,000	19,000,000	52,000,000	56,000,000
Expected return on plan assets	(16,000,000)	(17,000,000)	(49,000,000)	(51,000,000)
Amortization:
Prior service costs	0	2,000,000	2,000,000	5,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	(1,000,000)	3,000,000	(2,000,000)	10,000,000
Net periodic pension cost (income)	6,000,000	13,000,000	17,000,000	38,000,000
Postretirement Benefits | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000	3,000,000	4,000,000
Interest cost	4,000,000	5,000,000	12,000,000	13,000,000
Expected return on plan assets	(6,000,000)	(7,000,000)	(19,000,000)	(20,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000	3,000,000	3,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	0	0	0	1,000,000
Net periodic pension cost (income)	0	0	(1,000,000)	1,000,000
Postretirement Benefits | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	2,000,000	4,000,000	5,000,000
Interest cost	6,000,000	7,000,000	19,000,000	21,000,000
Expected return on plan assets	(7,000,000)	(6,000,000)	(19,000,000)	(19,000,000)
Amortization:
Prior service costs	0	0	0	1,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	1,000,000	2,000,000	1,000,000	6,000,000
Net periodic pension cost (income)	2,000,000	5,000,000	5,000,000	14,000,000
Postretirement Benefits | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	0	1,000,000	1,000,000
Interest cost	0	0	2,000,000	2,000,000
Expected return on plan assets	0	0	(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)	1,000,000	0	2,000,000	2,000,000
Postretirement Benefits | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	0	1,000,000	0	1,000,000
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	1,000,000	0	1,000,000
Postretirement Benefits | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	0	0	1,000,000	1,000,000
Interest cost	2,000,000	2,000,000	7,000,000	7,000,000
Expected return on plan assets	(1,000,000)	(1,000,000)	(4,000,000)	(5,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	1,000,000	2,000,000	4,000,000	5,000,000
Net (gain)/loss	0	0	(2,000,000)	0
Net periodic pension cost (income)	$ 2,000,000	$ 3,000,000	$ 6,000,000	$ 8,000,000