Receivables Narrative (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Sale Of Accounts Receivable - KCPL and GMO
Accounts receivable pledged as collateral	$ 173.7	$ 175.0
Collateralized note payable	173.7	175.0
Kansas City Power and Light Company [Member]
Sale Of Accounts Receivable - KCPL and GMO
Accounts receivable pledged as collateral	110.0	110.0
Collateralized note payable	110.0	$ 110.0
Maximum amount of outstanding principal under receivables agreement	110.0
KCPL Greater Missouri Operations [Member]
Sale Of Accounts Receivable - KCPL and GMO
Maximum amount of outstanding principal under receivables agreement from mid-November to mid-June	65.0
Maximum amount of outstanding principal under receivables agreement from mid-June to mid-November	$ 80.0

Maximum amount of outstanding principal under receivables agreement

No definition available.

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

- Definition

MaximumAmountOfOutstandingPrincipalUnderReceivablesAgreementFromMidJunToMidNov

+ References

No definition available.

+ Details

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

- Definition

MaximumAmountOfOutstandingPrincipalUnderReceivablesAgreementFromMidNovToMidJun

+ References

No definition available.

+ Details

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

- Definition

Sale Of Accounts Receivable - KCPL and GMO [Line Items] [Abstract]

+ References

No definition available.

+ Details

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

- Definition

Carrying amount of financial assets accounted for as secured borrowings recognized in the transferor's statement of financial position at the end of each period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=55761124&loc=SL6224234-111729

+ Details

Name:	us-gaap_TransfersAccountedForAsSecuredBorrowingsAssetsCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount of liabilities associated with financial assets accounted for as secured borrowings recognized in the transferor's statement of financial position at the end of each period presented.

+ References

+ Details

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

- Details

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

- Details

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