Name:	gxp_AnticipatedAcquisitionFinancingCommonAndPreferredEquity
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Anticipated amount of long-term debt to be issued to finance a portion of the cash consideration for the merger.

No definition available.

Name:	gxp_AnticipatedAcquisitionFinancingDebt
Namespace Prefix:	gxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Anticipated amount of mandatory convertible preferred equity to be issued to finance a portion of the cash consideration for the merger.

No definition available.

Name:	gxp_AnticipatedAcquisitionFinancingMandatoryConvertiblePreferredEquity
Namespace Prefix:	gxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Anticipated Acquisition Of Westar Energy, Inc.

No definition available.

Name:	gxp_AnticipatedAcquisitionOfWestarEnergyInc.LineItems
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Data Type:	xbrli:stringItemType
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Amount of cash consideration per share of the acquiree to be transferred by the acquirer.

No definition available.

Name:	gxp_AnticipatedBusinessCombinationCashConsiderationToBeTransferred
Namespace Prefix:	gxp_
Data Type:	num:perShareItemType
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Period Type:	duration

Exchange ratio if the Great Plains Energy Average Stock Price is greater than $33.2283.

No definition available.

Name:	gxp_ExchangeRatio1
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Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

Exchange Ratio if the Great Plains Energy Average Stock Price is less than $28.5918.

No definition available.

Name:	gxp_ExchangeRatio2
Namespace Prefix:	gxp_
Data Type:	xbrli:decimalItemType
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Period Type:	duration

Amount to be divided by the Great Plains Energy Average Stock Price if the Great Plains Energy Average Stock Price is greater than or equal to $28.5918 but less than or equal to $33.2283.

No definition available.

Name:	gxp_ExchangeRatioNumerator
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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

If the Great Plains Energy Average Stock Price is equal to or between these amounts, the Exchange Ratio will be an amount equal to the quotient obtained by dividing (x) $9.00 by (y) the Great Plains Energy Average Stock Price.

No definition available.

Name:	gxp_GreatPlainsEnergyAverageStockPriceLessThanMaximumGreaterThanMinimum
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Data Type:	num:perShareItemType
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If the Great Plains Energy Average Stock Price is greater than this amount, the Exchange Ratio will be 0.2709.

No definition available.

Name:	gxp_GreatPlainsEnergyAverageStockPriceMaximum
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Data Type:	num:perShareItemType
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Period Type:	duration

If the Great Plains Energy Average Stock Price is less than this amount, the Exchange Ratio will be 0.3148.

No definition available.

Name:	gxp_GreatPlainsEnergyAverageStockPriceMinimum
Namespace Prefix:	gxp_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility, as amended.

No definition available.

Name:	gxp_LineOfCreditFacilityMaximumBorrowingCapacityAsAmended
Namespace Prefix:	gxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Fee Great Plains Energy may be required to pay if the Merger Agreement is terminated by Westar as a result of the Great Plains Energy board of directors changing its recommendation to the Great Plains Energy shareholders as a result of a superior proposal prior to the Great Plains Energy shareholder approval having been obtained.

No definition available.

Name:	gxp_MergerTerminationFeeGreatPlainsEnergyBoardofDirectors
Namespace Prefix:	gxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Fee Great Plains Energy may be required to pay if the Merger Agreement is terminated by either Great Plains Energy or Westar as a result of the Great Plains Energy shareholders not approving the issuance of the Great Plains Energy Common Stock to the Westar shareholders in the merger.

No definition available.

Name:	gxp_MergerTerminationFeeGreatPlainsEnergyShareholders
Namespace Prefix:	gxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Fee that Great Plains Energy may be required to pay if the termination of the Merger Agreement under specified circumstances relating to a failure to obtain required regulatory approvals prior to May 31, 2017 (which date may be extended to November 30, 2017 under certain circumstances), a final and nonappealable order enjoining the consummation of the merger in connection with regulatory approvals or failure by Great Plains Energy to consummate the merger once all of the conditions have been satisfied.

No definition available.

Name:	gxp_MergerTerminationFeeRegulatoryApproval
Namespace Prefix:	gxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Fee Westar may be required to pay if the Merger Agreement is terminated by Westar under specified circumstances to enter into a definitive acquisition agreement with respect to a superior proposal or by Great Plains Energy as a result of Westar's board of directors changing its recommendation of the merger prior to the Westar shareholder approval having been obtained.

No definition available.

Name:	gxp_MergerTerminationFeeSuperiorProposal
Namespace Prefix:	gxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Number of 7.25% Mandatory Convertible Preferred Stock, Series A shares to be issued under the stock purchase agreement with OMERS.

No definition available.

Name:	gxp_PreferredSharesToBeIssuedStockPurchaseAgreementSeriesAPreferredStock
Namespace Prefix:	gxp_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Amount of proceeds to be received for sale of 7.25% Mandatory Convertible Preferred Stock, Series A, without par value at the closing of the merger.

No definition available.

Name:	gxp_PreferredStockPurchaseAgreementProceeds
Namespace Prefix:	gxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The percentage rate used to calculate dividend payments on preferred stock.

No definition available.

Name:	us-gaap_PreferredStockDividendRatePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Name:	dei_LegalEntityAxis=us-gaap_ParentCompanyMember
Namespace Prefix:
Data Type:	na
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Period Type:

Name:	dei_LegalEntityAxis=gxp_WestarEnergyIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_CreditFacilityAxis=us-gaap_BridgeLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_SeriesAPreferredStockMember
Namespace Prefix:
Data Type:	na
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Period Type:

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
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