Regulatory Matters Asset (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 849.7		$ 1,120.9
Taxes recoverable through future rates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	136.4		138.4
Loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	8.6		10.1
Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	1.0		2.8
Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	50.8		46.4
Pension and post-retirement costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	401.2		670.9
Deferred customer programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	72.0		74.4
Rate case expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	4.2		9.2
Fuel recovery mechanisms [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	23.6		25.8
Acquisition transition costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	23.9		34.2
Derivative instruments [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0		3.7
Iatan No. 1 and Common facilities depreciation and carrying costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	21.0		21.8
Iatan No. 2 construction accounting costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	45.3		46.8
Kansas property tax surcharge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	4.0		5.4
Solar Rebates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	45.3		15.8
Voluntary Separation Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	3.4		4.3
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	9.0		10.9
Kansas City Power and Light Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	614.1		853.2
Kansas City Power and Light Company [Member] | Taxes recoverable through future rates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	111.0		114.7
Kansas City Power and Light Company [Member] | Loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	7.1	[1]	8.1
Regulatory amortization period	over the life of the related new debt issuances or the remaining lives of the old debt issuances if no new debt was issued.
Kansas City Power and Light Company [Member] | Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	1.0		2.8
Kansas City Power and Light Company [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	34.8		31.5
Kansas City Power and Light Company [Member] | Pension and post-retirement costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	310.0	[2]	541.2
Amount not included in rate base	288.5
Regulatory amortization period	various
Kansas City Power and Light Company [Member] | Deferred customer programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	50.2	[3]	49.8
Amount not included in rate base	15.4
Regulatory amortization period	various
Kansas City Power and Light Company [Member] | Rate case expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	3.6	[4]	7.5
Regulatory amortization period	various
Kansas City Power and Light Company [Member] | Fuel recovery mechanisms [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	10.8	[4]	8.9
Regulatory amortization period	various
Kansas City Power and Light Company [Member] | Acquisition transition costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	12.9	[5]	18.7
Regulatory amortization period	through 2016
Kansas City Power and Light Company [Member] | Derivative instruments [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0		0
Kansas City Power and Light Company [Member] | Iatan No. 1 and Common facilities depreciation and carrying costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	15.3	[6]	15.9
Regulatory amortization period	through 2038
Kansas City Power and Light Company [Member] | Iatan No. 2 construction accounting costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	29.3	[7]	30.6
Regulatory amortization period	through 2058
Kansas City Power and Light Company [Member] | Kansas property tax surcharge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	4.0	[4]	5.4
Regulatory amortization period	various
Kansas City Power and Light Company [Member] | Solar Rebates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	13.0	[4]	5.8
Regulatory amortization period	various
Kansas City Power and Light Company [Member] | Voluntary Separation Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	3.4	[8]	4.3
Regulatory amortization period	through 2017
Kansas City Power and Light Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	7.7	[4]	8.0
Regulatory amortization period	various
KCPL Greater Missouri Operations [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	235.6		267.7
KCPL Greater Missouri Operations [Member] | Taxes recoverable through future rates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	25.4		23.7
KCPL Greater Missouri Operations [Member] | Loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	1.5	[1]	2.0
Regulatory amortization period	over the life of the related new debt issuances or the remaining lives of the old debt issuances if no new debt was issued.
KCPL Greater Missouri Operations [Member] | Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0		0
KCPL Greater Missouri Operations [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	16.0		14.9
KCPL Greater Missouri Operations [Member] | Pension and post-retirement costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	91.2	[2]	129.7
Amount not included in rate base	57.0
Regulatory amortization period	various
KCPL Greater Missouri Operations [Member] | Deferred customer programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	21.8	[9]	24.6
Amount not included in rate base	2.1
Regulatory amortization period	various
KCPL Greater Missouri Operations [Member] | Rate case expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0.6	[10]	1.7
Regulatory amortization period	through 2014
KCPL Greater Missouri Operations [Member] | Fuel recovery mechanisms [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	12.8	[4]	16.9
Regulatory amortization period	various
KCPL Greater Missouri Operations [Member] | Acquisition transition costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	11.0	[5]	15.5
Regulatory amortization period	through 2016
KCPL Greater Missouri Operations [Member] | Derivative instruments [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0	[6]	3.7
KCPL Greater Missouri Operations [Member] | Iatan No. 1 and Common facilities depreciation and carrying costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	5.7	[6]	5.9
Regulatory amortization period	through 2038
KCPL Greater Missouri Operations [Member] | Iatan No. 2 construction accounting costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	16.0	[7]	16.2
Regulatory amortization period	through 2058
KCPL Greater Missouri Operations [Member] | Kansas property tax surcharge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0		0
KCPL Greater Missouri Operations [Member] | Solar Rebates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	32.3	[4]	10.0
Regulatory amortization period	various
KCPL Greater Missouri Operations [Member] | Voluntary Separation Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0		0
KCPL Greater Missouri Operations [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 1.3	[4]	$ 2.9
Regulatory amortization period	various

[1] Amortized over the life of the related new debt issuances or the remaining lives of the old debt issuances if no new debt was issued.

[2] Represents unrecognized gains and losses, prior service and transition costs that will be recognized in future net periodic pension and post-retirement costs, pension settlements amortized over various periods and financial and regulatory accounting method differences that will be eliminated over the life of the pension plans. Of these amounts, $288.5 million and $57.0 million for KCP&L and GMO, respectively, are not included in rate base and are amortized over various periods.

[3] $15.4 million not included in rate base and amortized over various periods.

[4] Not included in rate base and amortized over various periods.

[5] Not included in rate base and amortized through 2016.

[6] Included in rate base and amortized through 2038.

[7] Included in rate base and amortized through 2058.

[8] Not included in rate base and amortized through 2017.

[9] $2.1 million not included in rate base and amortized over various periods.

[10] Not included in rate base and amortized through 2014.