Retirement Benefits (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	$ 0		$ 0
Pension Plans \| Southern Company
Pension Plans and Postretirement Plans
Service cost	74,000,000	$ 62,000,000	147,000,000	$ 124,000,000
Interest cost	113,000,000	101,000,000	227,000,000	201,000,000
Expected return on plan assets	(225,000,000)	(187,000,000)	(449,000,000)	(374,000,000)
Amortization:
Prior service costs	3,000,000	3,000,000	6,000,000	7,000,000
Net (gain)/loss	41,000,000	37,000,000	81,000,000	75,000,000
Net periodic pension cost (income)	6,000,000	16,000,000	12,000,000	33,000,000
Pension Plans \| SOUTHERN Co GAS
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	5,000,000		11,000,000
Interest cost	10,000,000		20,000,000
Expected return on plan assets	(17,000,000)		(35,000,000)
Amortization:
Prior service costs	(1,000,000)		(1,000,000)
Net (gain)/loss	5,000,000		10,000,000
Net periodic pension cost (income)	2,000,000		5,000,000
Pension Plans \| ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	16,000,000	15,000,000	32,000,000	29,000,000
Interest cost	24,000,000	24,000,000	48,000,000	48,000,000
Expected return on plan assets	(49,000,000)	(46,000,000)	(98,000,000)	(92,000,000)
Amortization:
Prior service costs	0	0	1,000,000	1,000,000
Net (gain)/loss	11,000,000	10,000,000	21,000,000	20,000,000
Net periodic pension cost (income)	2,000,000	3,000,000	4,000,000	6,000,000
Pension Plans \| GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	18,000,000	18,000,000	37,000,000	35,000,000
Interest cost	35,000,000	34,000,000	69,000,000	68,000,000
Expected return on plan assets	(70,000,000)	(65,000,000)	(141,000,000)	(129,000,000)
Amortization:
Prior service costs	1,000,000	2,000,000	2,000,000	3,000,000
Net (gain)/loss	14,000,000	13,000,000	28,000,000	27,000,000
Net periodic pension cost (income)	(2,000,000)	2,000,000	(5,000,000)	4,000,000
Pension Plans \| GULF POWER CO
Pension Plans and Postretirement Plans
Service cost	4,000,000	3,000,000	7,000,000	6,000,000
Interest cost	5,000,000	4,000,000	10,000,000	9,000,000
Expected return on plan assets	(9,000,000)	(8,000,000)	(19,000,000)	(17,000,000)
Amortization:
Prior service costs	0	1,000,000	0	1,000,000
Net (gain)/loss	1,000,000	1,000,000	3,000,000	3,000,000
Net periodic pension cost (income)	1,000,000	1,000,000	1,000,000	2,000,000
Pension Plans \| MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	3,000,000	3,000,000	7,000,000	6,000,000
Interest cost	5,000,000	5,000,000	10,000,000	10,000,000
Expected return on plan assets	(10,000,000)	(8,000,000)	(20,000,000)	(17,000,000)
Amortization:
Prior service costs	1,000,000	0	1,000,000	0
Net (gain)/loss	2,000,000	1,000,000	4,000,000	3,000,000
Net periodic pension cost (income)	1,000,000	1,000,000	2,000,000	2,000,000
Postretirement Benefits \| Southern Company
Pension Plans and Postretirement Plans
Service cost	6,000,000	6,000,000	12,000,000	11,000,000
Interest cost	20,000,000	17,000,000	40,000,000	35,000,000
Expected return on plan assets	(17,000,000)	(14,000,000)	(33,000,000)	(28,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000	3,000,000	3,000,000
Net (gain)/loss	5,000,000	4,000,000	7,000,000	7,000,000
Net periodic pension cost (income)	15,000,000	14,000,000	29,000,000	28,000,000
Postretirement Benefits \| SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	0		1,000,000
Interest cost	2,000,000		5,000,000
Expected return on plan assets	(1,000,000)		(3,000,000)
Amortization:
Prior service costs	0		(1,000,000)
Net (gain)/loss	1,000,000		2,000,000
Net periodic pension cost (income)	2,000,000		4,000,000
Postretirement Benefits \| ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	2,000,000	3,000,000	3,000,000
Interest cost	4,000,000	4,000,000	9,000,000	9,000,000
Expected return on plan assets	(8,000,000)	(7,000,000)	(14,000,000)	(13,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000	2,000,000	2,000,000
Net (gain)/loss	1,000,000	1,000,000	1,000,000	1,000,000
Net periodic pension cost (income)	0	1,000,000	1,000,000	2,000,000
Postretirement Benefits \| GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000	3,000,000	3,000,000
Interest cost	8,000,000	7,000,000	15,000,000	15,000,000
Expected return on plan assets	(6,000,000)	(5,000,000)	(12,000,000)	(11,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000	1,000,000	1,000,000
Net (gain)/loss	1,000,000	2,000,000	3,000,000	4,000,000
Net periodic pension cost (income)	5,000,000	6,000,000	10,000,000	12,000,000
Postretirement Benefits \| GULF POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000	1,000,000	1,000,000
Interest cost	0	0	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
Net (gain)/loss	0	0	0	0
Net periodic pension cost (income)	0	0	1,000,000	1,000,000
Postretirement Benefits \| MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000	1,000,000	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
Net (gain)/loss	0	0	0	0
Net periodic pension cost (income)	$ 1,000,000	1,000,000	$ 2,000,000	2,000,000
Predecessor \| Pension Plans \| SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost		7,000,000		13,000,000
Interest cost		11,000,000		21,000,000
Expected return on plan assets		(17,000,000)		(33,000,000)
Amortization:
Prior service costs		(1,000,000)		(1,000,000)
Net (gain)/loss		7,000,000		13,000,000
Net periodic pension cost (income)		7,000,000		13,000,000
Predecessor \| Postretirement Benefits \| SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost		0		1,000,000
Interest cost		2,000,000		5,000,000
Expected return on plan assets		(1,000,000)		(3,000,000)
Amortization:
Prior service costs		0		(1,000,000)
Net (gain)/loss		1,000,000		2,000,000
Net periodic pension cost (income)		$ 2,000,000		$ 4,000,000

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

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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 prior service cost (credit) 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2709-114920

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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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Amount of cost recognized for passage of time related to defined benefit plan.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(2)
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Amount of net periodic benefit cost (credit) for defined benefit plan.

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Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(1)
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