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

Name:	gxp_AirAndClimateChangeAbstract
Namespace Prefix:	gxp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	gxp_BestAvailableRetrofitTechnologyRuleAbstract
Namespace Prefix:	gxp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

New MACT rules will apply to all new or existing coal-fired electric generating units with a capacity equal to or greater than this amount.

No definition available.

Name:	gxp_CapacityOfElectricSteamGeneratingUnitsThatFallUnderMactStandardsInMw
Namespace Prefix:	gxp_
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	instant

The amount of cash capital expenditures that have been incurred since commencement of the La Cygne environmental project and are included in the Company's total estimate of capital expenditures to comply with environmental regulations.

No definition available.

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

Name:	gxp_CleanAirInterstateRuleAndTransportRuleAbstract
Namespace Prefix:	gxp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	gxp_ClimateChangeAbstract
Namespace Prefix:	gxp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the estimated cost to install a selective catalytic reduction system at Jeffrey Energy Center pursuant to a settlement agreement related to Westar Energy, Incorporated's alleged Clean Air Act violations.

No definition available.

Name:	gxp_CostToInstallSelectiveCatalyticReductionSystem
Namespace Prefix:	gxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the current estimate of capital expenditures (exclusive of AFUDC and property taxes) required to comply with the currently effective Clean Air Interstate Rule CAIR, the replacement to CAIR or the Cross-State Air Pollution Rule, and with the best available retrofit technology rule, the SO2 national ambient air quality standard, the industrial boiler rule and proposed maximum achievable control technology standards for mercury and other hazardous air pollutant emissions.

No definition available.

Name:	gxp_CurrentEstimateOfCapitalExpenditures
Namespace Prefix:	gxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the estimated amount of insurance proceeds available, less an annual deductible, to GMO cover qualified MGP remediation expenses.

No definition available.

Name:	gxp_EstimatedDollarAmountOfAvailableInsuranceProceedsToCoverQualifiedRemediationExpense
Namespace Prefix:	gxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the company-specific estimated megawatts of electricity required to be provided by KCPL and GMO to their Missouri retail customers from solar resources by 2011, pursuant to a law passed in 2008.

No definition available.

Name:	gxp_EstimatedNumberOfMegawattsOfMissouriElectricityToComeFromSolarResources
Namespace Prefix:	gxp_
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	instant

Represents the estimated number of tons of CO2 produced each year based on current generation capacity.

No definition available.

Name:	gxp_EstimatedNumberOfTonsOfCo2ProducedPerYear
Namespace Prefix:	gxp_
Data Type:	num:massItemType
Balance Type:	na
Period Type:	instant

KCPL's share of the amount of the predetermination request in Kansas for environmental equipment required at LaCygne Station to comply with BART.

No definition available.

Name:	gxp_KcplShareOfPredeterminationRequestForEnvironmentalEquipmentRequiredAtLacygneStationToComplyWithBart
Namespace Prefix:	gxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Name:	gxp_MercuryAndOtherHazardousAirPollutantEmissionsAbstract
Namespace Prefix:	gxp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the renewable energy generation capacity based on a three-year average of Kansas peak retail demand required to be in place by 2020. This law was passed in 2009 and applies to all Kansas public electric utilities, including KCPL.

No definition available.

Name:	gxp_MinimumPercentageOfKansasRenewableEnergyGenerationCapacityBasedOnThreeYearAveragePeakRetailDemandByYearEleven
Namespace Prefix:	gxp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the renewable energy generation capacity based on a three-year average of Kansas peak retail demand required to be in place by 2016. This law was passed in 2009 and applies to all Kansas public electric utilities, including KCPL.

No definition available.

Name:	gxp_MinimumPercentageOfKansasRenewableEnergyGenerationCapacityBasedOnThreeYearAveragePeakRetailDemandByYearSeven
Namespace Prefix:	gxp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the renewable energy generation capacity based on a three-year average of Kansas peak retail demand required to be in place by 2011. This law was passed in 2009 and applies to all Kansas public electric utilities, including KCPL.

No definition available.

Name:	gxp_MinimumPercentageOfKansasRenewableEnergyGenerationCapacityBasedOnThreeYearAveragePeakRetailDemandByYearTwo
Namespace Prefix:	gxp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the percentage of electricity provided by Missouri investor-owned utilities (including KCPL and GMO) to their Missouri retail customers required to come from renewable resources by 2014, pursuant to a law passed in 2008.

No definition available.

Name:	gxp_MinimumPercentageOfMissouriElectricityToComeFromRenewableResourcesForRetailCustomersByYearSix
Namespace Prefix:	gxp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

No definition available.

Name:	gxp_MinimumPercentageOfMissouriElectricityToComeFromRenewableResourcesForRetailCustomersByYearTen
Namespace Prefix:	gxp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

No definition available.

Name:	gxp_MinimumPercentageOfMissouriElectricityToComeFromRenewableResourcesForRetailCustomersByYearThirteen
Namespace Prefix:	gxp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

No definition available.

Name:	gxp_MinimumPercentageOfMissouriElectricityToComeFromRenewableResourcesForRetailCustomersByYearThree
Namespace Prefix:	gxp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Name:	gxp_NewSourceReviewAbstract
Namespace Prefix:	gxp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the number of states required to reduce emissions of SO2 and NOX under the CAIR, including Missouri.

No definition available.

Name:	gxp_NumberOfStatesRequiredToReduceEmissionsUnderCair
Namespace Prefix:	gxp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

The amount of the predetermination request in Kansas for environmental equipment required at LaCygne Station to comply with BART.

No definition available.

Name:	gxp_PredeterminationRequestForEnvironmentalEquipmentRequiredAtLacygneStationToComplyWithBart
Namespace Prefix:	gxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Name:	gxp_RemediationAbstract
Namespace Prefix:	gxp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the primary one-hour sulfur dioxide standard as revised by the Environmental Protection Agency in June 2010 to replace the exisiting 24-hour and one-year standards.

No definition available.

Name:	gxp_RevisedPartsPerMillionForSulphurDioxideEstablishedForPrimaryStandard
Namespace Prefix:	gxp_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

Represents the primary twenty-four hour sulfur dioxide standard revoked by the Environmental Protection Agency in June 2010.

No definition available.

Name:	gxp_RevokedPartsPerMillionForSulphurDioxideForPrimaryStandardOver1Day
Namespace Prefix:	gxp_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

Represents the primary one-year sulfur dioxide standard revoked by the Environmental Protection Agency in June 2010.

No definition available.

Name:	gxp_RevokedPartsPerMillionForSulphurDioxideForPrimaryStandardOver1Year
Namespace Prefix:	gxp_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

Name:	gxp_So2NationalAmbientAirQualityStandardAbstract
Namespace Prefix:	gxp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Total costs accrued as of the balance sheet date for environmental loss contingencies.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 25

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9

-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.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 30

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

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-Publisher AICPA

-Name Statement of Position (SOP)

-Number 96-1

-Paragraph 161

-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.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6952336&loc=d3e14326-108349

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

The proportionate share of interest (percent) in a jointly owned utility plant.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 10.C)

-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section C