Financing - Outstanding Classes of Capital Stock (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance	$ 118
Redeemed	(658)	$ 0	$ (412)
Ending balance	$ 324	$ 118
MISSISSIPPI POWER CO
Increase (Decrease) in Temporary Equity [Roll Forward]
Temporary equity, shares outstanding (in shares)	334,210	334,210
Dividend rate, maximum	5.25%	5.25%
Redeemable Preferred Stock
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance	$ 118	$ 118	375
Issued	250	0	0
Redeemed	(38)	0	(262)
Issuance Costs	(6)		5
Ending balance	$ 324	$ 118	$ 118
Depositary Shares \| MISSISSIPPI POWER CO
Increase (Decrease) in Temporary Equity [Roll Forward]
Temporary equity, shares outstanding (in shares)	1,200,000,000,000

Preferred stock dividend rate stated percentage rate range maximum.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

The cash outflow to reacquire preferred stock during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

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- Definition

Carrying amount, attributable to parent, of an entity's issued and outstanding stock which is not included within permanent equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer.

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- Definition

Amount of increase (decrease) in temporary equity from changes classified as other.

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No definition available.

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- Definition

The number of securities classified as temporary equity that have been issued and are held by the entity's shareholders. Securities outstanding equals securities issued minus securities held in treasury. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(27)(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Value of new stock classified as temporary equity issued during the period.

+ References

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