Name:	gxp_PercentageOfExpectedOnPeakNaturalGasAndNaturalGasEquivalentPurchasedPowerPriceExposureHedgedYearOne
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Percentage of projected natural gas usage hedged for the third year following the balance sheet date.

No definition available.

Name:	gxp_PercentageOfExpectedOnPeakNaturalGasAndNaturalGasEquivalentPurchasedPowerPriceExposureHedgedYearThree
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Data Type:	num:percentItemType
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Percentage of expected on-peak natural gas and natural gas equivalent purchased power price exposure that is hedged for the second year following the balance sheet date.

No definition available.

Name:	gxp_PercentageOfExpectedOnPeakNaturalGasAndNaturalGasEquivalentPurchasedPowerPriceExposureHedgedYearTwo
Namespace Prefix:	gxp_
Data Type:	num:percentItemType
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Period Type:	instant

Percentage of projected natural gas usage hedged for the year following the balance sheet date.

No definition available.

Name:	gxp_PercentageOfProjectedNaturalGasUsageHedgedYearOne
Namespace Prefix:	gxp_
Data Type:	num:percentItemType
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Period Type:	instant

Percentage of projected natural gas usage hedged for the second year following the balance sheet date.

No definition available.

Name:	gxp_PercentageOfProjectedNaturalGasUsageHedgedYearTwo
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Data Type:	num:percentItemType
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Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

The net amount as of the balance sheet date of the fair value of derivative assets and derivative liabilities that in accordance with the entity's accounting policy were not offset against collateral under a master netting arrangement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=d3e41678-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FIN39-1

-Paragraph 10B

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.