Retirement Benefits (Details) - USD ($)	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	$ 0
Pension Plan [Member] \| Southern Company Gas [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	0
Pension Plans and Postretirement Plans
Service cost	6,000,000
Interest cost	10,000,000
Expected return on plan assets	(18,000,000)
Amortization:
Prior service costs	0
Net (gain)/loss	5,000,000
Net periodic pension cost (income)	3,000,000
Pension Plan [Member] \| Southern Company [Member]
Pension Plans and Postretirement Plans
Service cost	73,000,000	$ 62,000,000
Interest cost	114,000,000	100,000,000
Expected return on plan assets	(224,000,000)	(187,000,000)
Amortization:
Prior service costs	3,000,000	4,000,000
Net (gain)/loss	40,000,000	38,000,000
Net periodic pension cost (income)	6,000,000	17,000,000
Pension Plan [Member] \| Alabama Power [Member]
Pension Plans and Postretirement Plans
Service cost	16,000,000	14,000,000
Interest cost	24,000,000	24,000,000
Expected return on plan assets	(49,000,000)	(46,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000
Net (gain)/loss	10,000,000	10,000,000
Net periodic pension cost (income)	2,000,000	3,000,000
Pension Plan [Member] \| Georgia Power [Member]
Pension Plans and Postretirement Plans
Service cost	19,000,000	17,000,000
Interest cost	34,000,000	34,000,000
Expected return on plan assets	(71,000,000)	(64,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000
Net (gain)/loss	14,000,000	14,000,000
Net periodic pension cost (income)	(3,000,000)	2,000,000
Pension Plan [Member] \| Gulf Power [Member]
Pension Plans and Postretirement Plans
Service cost	3,000,000	3,000,000
Interest cost	5,000,000	5,000,000
Expected return on plan assets	(10,000,000)	(9,000,000)
Amortization:
Prior service costs	0	0
Net (gain)/loss	2,000,000	2,000,000
Net periodic pension cost (income)	0	1,000,000
Pension Plan [Member] \| Mississippi Power [Member]
Pension Plans and Postretirement Plans
Service cost	4,000,000	3,000,000
Interest cost	5,000,000	5,000,000
Expected return on plan assets	(10,000,000)	(9,000,000)
Amortization:
Prior service costs	0	0
Net (gain)/loss	2,000,000	2,000,000
Net periodic pension cost (income)	1,000,000	1,000,000
Other Postretirement Benefit Plan [Member] \| Southern Company Gas [Member]
Pension Plans and Postretirement Plans
Service cost	1,000,000
Interest cost	3,000,000
Expected return on plan assets	(2,000,000)
Amortization:
Prior service costs	(1,000,000)
Net (gain)/loss	1,000,000
Net periodic pension cost (income)	2,000,000
Other Postretirement Benefit Plan [Member] \| Southern Company [Member]
Pension Plans and Postretirement Plans
Service cost	6,000,000	5,000,000
Interest cost	20,000,000	18,000,000
Expected return on plan assets	(16,000,000)	(14,000,000)
Amortization:
Prior service costs	2,000,000	2,000,000
Net (gain)/loss	2,000,000	3,000,000
Net periodic pension cost (income)	14,000,000	14,000,000
Other Postretirement Benefit Plan [Member] \| Alabama Power [Member]
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000
Interest cost	5,000,000	5,000,000
Expected return on plan assets	(6,000,000)	(6,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000
Net (gain)/loss	0	0
Net periodic pension cost (income)	1,000,000	1,000,000
Other Postretirement Benefit Plan [Member] \| Georgia Power [Member]
Pension Plans and Postretirement Plans
Service cost	2,000,000	2,000,000
Interest cost	7,000,000	8,000,000
Expected return on plan assets	(6,000,000)	(6,000,000)
Amortization:
Prior service costs	0	0
Net (gain)/loss	2,000,000	2,000,000
Net periodic pension cost (income)	5,000,000	6,000,000
Other Postretirement Benefit Plan [Member] \| Gulf Power [Member]
Pension Plans and Postretirement Plans
Service cost	0	0
Interest cost	1,000,000	1,000,000
Expected return on plan assets	0	0
Amortization:
Prior service costs	0	0
Net (gain)/loss	0	0
Net periodic pension cost (income)	1,000,000	1,000,000
Other Postretirement Benefit Plan [Member] \| Mississippi Power [Member]
Pension Plans and Postretirement Plans
Service cost	0	0
Interest cost	1,000,000	1,000,000
Expected return on plan assets	0	0
Amortization:
Prior service costs	0	0
Net (gain)/loss	0	0
Net periodic pension cost (income)	$ 1,000,000	1,000,000
Predecessor [Member] \| Pension Plan [Member] \| Southern Company Gas [Member]
Pension Plans and Postretirement Plans
Service cost		6,000,000
Interest cost		10,000,000
Expected return on plan assets		(16,000,000)
Amortization:
Prior service costs		0
Net (gain)/loss		6,000,000
Net periodic pension cost (income)		6,000,000
Predecessor [Member] \| Other Postretirement Benefit Plan [Member] \| Southern Company Gas [Member]
Pension Plans and Postretirement Plans
Service cost		1,000,000
Interest cost		3,000,000
Expected return on plan assets		(2,000,000)
Amortization:
Prior service costs		(1,000,000)
Net (gain)/loss		1,000,000
Net periodic pension cost (income)		$ 2,000,000

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

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The amount of gains or losses recognized in net periodic benefit cost.

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- Definition

The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.

+ References

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)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Prior Service Cost
-URI http://asc.fasb.org/extlink&oid=49177896

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Expected Return on Plan Assets
-URI http://asc.fasb.org/extlink&oid=6512171

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- Definition

The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Topic 715
-SubTopic 20
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-Paragraph 1
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The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

+ References

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

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- Definition

The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Service Cost (Component of Net Periodic Pension Cost)
-URI http://asc.fasb.org/extlink&oid=6525008

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- Definition

Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position.

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