Retirement Benefits (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	89,000,000	146,000,000	$ 179,000,000
Interest cost	123,000,000	116,000,000	246,000,000	232,000,000
Expected return on plan assets	(221,000,000)	(235,000,000)	(442,000,000)	(471,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000	1,000,000	2,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	30,000,000	54,000,000	60,000,000	107,000,000
Net periodic pension cost (income)	6,000,000	25,000,000	11,000,000	49,000,000
Pension Plans \| ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	17,000,000	20,000,000	34,000,000	39,000,000
Interest cost	29,000,000	25,000,000	57,000,000	50,000,000
Expected return on plan assets	(52,000,000)	(53,000,000)	(103,000,000)	(104,000,000)
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	9,000,000	13,000,000	18,000,000	27,000,000
Net periodic pension cost (income)	4,000,000	6,000,000	7,000,000	13,000,000
Pension Plans \| GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	18,000,000	21,000,000	37,000,000	43,000,000
Interest cost	39,000,000	35,000,000	78,000,000	70,000,000
Expected return on plan assets	(73,000,000)	(74,000,000)	(146,000,000)	(148,000,000)
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	11,000,000	17,000,000	22,000,000	34,000,000
Net periodic pension cost (income)	(4,000,000)	0	(8,000,000)	0
Pension Plans \| MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	3,000,000	4,000,000	6,000,000	8,000,000
Interest cost	5,000,000	5,000,000	11,000,000	10,000,000
Expected return on plan assets	(10,000,000)	(10,000,000)	(20,000,000)	(20,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	0	0	0	0
Net (gain)/loss	2,000,000	2,000,000	3,000,000	5,000,000
Net periodic pension cost (income)	0	1,000,000	0	3,000,000
Pension Plans \| SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	2,000,000	3,000,000	4,000,000
Interest cost	2,000,000	2,000,000	3,000,000	3,000,000
Expected return on plan assets	(3,000,000)	(2,000,000)	(5,000,000)	(5,000,000)
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)	0	2,000,000	1,000,000	3,000,000
Pension Plans \| SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	6,000,000	8,000,000	12,000,000	16,000,000
Interest cost	9,000,000	9,000,000	18,000,000	19,000,000
Expected return on plan assets	(15,000,000)	(17,000,000)	(30,000,000)	(35,000,000)
Amortization:
Prior service costs	0	0	(1,000,000)	(1,000,000)
Regulatory asset	4,000,000	4,000,000	7,000,000	7,000,000
Net (gain)/loss	0	3,000,000	1,000,000	6,000,000
Net periodic pension cost (income)	4,000,000	7,000,000	7,000,000	12,000,000
Postretirement Benefits
Pension Plans and Postretirement Plans
Service cost	4,000,000	6,000,000	9,000,000	12,000,000
Interest cost	17,000,000	18,000,000	34,000,000	37,000,000
Expected return on plan assets	(17,000,000)	(17,000,000)	(33,000,000)	(34,000,000)
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	0	4,000,000	(1,000,000)	7,000,000
Net periodic pension cost (income)	5,000,000	12,000,000	11,000,000	25,000,000
Postretirement Benefits \| ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	2,000,000	2,000,000	3,000,000
Interest cost	4,000,000	4,000,000	8,000,000	8,000,000
Expected return on plan assets	(7,000,000)	(7,000,000)	(13,000,000)	(13,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000	2,000,000	2,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	0	1,000,000	0	1,000,000
Net periodic pension cost (income)	(1,000,000)	1,000,000	(1,000,000)	1,000,000
Postretirement Benefits \| GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000	2,000,000	3,000,000
Interest cost	6,000,000	7,000,000	13,000,000	14,000,000
Expected return on plan assets	(6,000,000)	(7,000,000)	(12,000,000)	(13,000,000)
Amortization:
Prior service costs	0	1,000,000	0	1,000,000
Regulatory asset	0	0	0	0
Net (gain)/loss	0	2,000,000	0	4,000,000
Net periodic pension cost (income)	1,000,000	4,000,000	3,000,000	9,000,000
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	2,000,000	2,000,000
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	1,000,000	2,000,000
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	0	0	1,000,000	1,000,000
Interest cost	3,000,000	3,000,000	5,000,000	5,000,000
Expected return on plan assets	(1,000,000)	(2,000,000)	(3,000,000)	(4,000,000)
Amortization:
Prior service costs	0	0	0	0
Regulatory asset	1,000,000	2,000,000	3,000,000	3,000,000
Net (gain)/loss	(1,000,000)	0	(2,000,000)	0
Net periodic pension cost (income)	$ 2,000,000	$ 3,000,000	$ 4,000,000	$ 5,000,000

Defined Benefit Plan, Net Periodic Benefit Cost, Amortization [Abstract]

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The expense charged against earnings during the period to allocate the capitalized costs of regulatory assets over the periods expected to benefit from such costs.

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Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan.

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Amount of contributions expected to be received by defined benefit plan from employer in fiscal year. Excludes contributions paid by employer in current fiscal year.

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Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan.

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