Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Assets [Abstract]
Derivative instruments, assets	$ 11.9		$ 7.8
Liabilities [Abstract]
Derivative instruments, liabilities	0.2		0.1
Kansas City Power and Light Company [Member]
Assets [Abstract]
Derivative instruments, assets	4.1		1.1
Liabilities [Abstract]
Derivative instruments, liabilities	0.2		0
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Assets [Abstract]
Derivative instruments, assets	11.9	[1]	7.8	[1]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	187.4	[2]	183.9	[2]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	16.2	[3]	14.8	[3]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	18.4	[4]	18.7	[4]
Total assets	233.9		225.2
Liabilities [Abstract]
Derivative instruments, liabilities	0.2	[1]	0.1	[1]
Total liabilities	0.2		0.1
Fair Value, Measurements, Recurring [Member] | Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash collateral posted with third parties as part of netting agreements	0.3		0.2
Assets [Abstract]
Derivative instruments, assets	(2.7)	[1],[5]	(0.7)	[1],[5]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	[2],[5]	0	[2],[5]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	[3]	0	[3]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0	[4],[5]	0	[4],[5]
Total assets	(2.7)	[5]	(0.7)	[5]
Liabilities [Abstract]
Derivative instruments, liabilities	(3.0)	[1],[5]	(0.9)	[1],[5]
Total liabilities	(3.0)	[5]	(0.9)	[5]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative instruments, assets	0.7	[1]	0.3	[1]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	155.0	[2]	152.7	[2]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	7.0	[3]	4.8	[3]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0.1	[4]	0.1	[4]
Total assets	162.8		157.9
Liabilities [Abstract]
Derivative instruments, liabilities	0.8	[1]	0.9	[1]
Total liabilities	0.8		0.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Derivative instruments, assets	4.6	[1]	4.9	[1]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	32.4	[2]	31.2	[2]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	9.2	[3]	10.0	[3]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	18.3	[4]	18.6	[4]
Total assets	64.5		64.7
Liabilities [Abstract]
Derivative instruments, liabilities	0	[1]	0.1	[1]
Total liabilities	0		0.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets	9.3	[1]	3.3	[1]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	[2]	0	[2]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	[3]	0	[3]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0	[4]	0	[4]
Total assets	9.3		3.3
Liabilities [Abstract]
Derivative instruments, liabilities	2.4	[1]	0	[1]
Total liabilities	2.4		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member]
Assets [Abstract]
Derivative instruments, assets	4.1		1.1
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	187.4		183.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	16.2		14.8
SERP rabbi trust [Abstract]
Total assets	207.7		199.8
Liabilities [Abstract]
Derivative instruments, liabilities	0.2	[1]	0	[1]
Total liabilities	0.2		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	129.3		127.7
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	1.2		0.9
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	9.2		9.3
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	22.0		21.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	3.3		2.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	4.0		3.9
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	24.2		24.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.5		0.5
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	3.7		3.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Other Assets [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.4		(0.4)
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure			1.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	5.8		3.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member]
Assets [Abstract]
Derivative instruments, assets	(1.7)	[5]	(0.1)	[5]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	[5]	0	[5]
SERP rabbi trust [Abstract]
Total assets	(1.7)	[5]	(0.1)	[5]
Liabilities [Abstract]
Derivative instruments, liabilities	(2.0)	[1],[5]	(0.3)	[1],[5]
Total liabilities	(2.0)	[5]	(0.3)	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | Other Assets [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure			0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative instruments, assets	0.2		0.1
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	155.0		152.7
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	7.0		4.8
SERP rabbi trust [Abstract]
Total assets	162.2		157.6
Liabilities [Abstract]
Derivative instruments, liabilities	0.5	[1]	0.3	[1]
Total liabilities	0.5		0.3
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	129.3		127.7
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	1.2		0.9
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0		0.5
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	22.0		21.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	3.7		3.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Other Assets [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure			0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	5.8		3.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Derivative instruments, assets	0		0
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	32.4		31.2
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	9.2		10.0
SERP rabbi trust [Abstract]
Total assets	41.6		41.2
Liabilities [Abstract]
Derivative instruments, liabilities	0	[1]	0	[1]
Total liabilities	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	9.2		8.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	3.3		2.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	4.0		3.9
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	24.2		24.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.5		0.5
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Other Assets [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.4		(0.4)
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure			1.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets	5.6		1.1
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0		0
SERP rabbi trust [Abstract]
Total assets	5.6		1.1
Liabilities [Abstract]
Derivative instruments, liabilities	1.7	[1]	0	[1]
Total liabilities	1.7		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Other Assets [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure			0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Estimate of Fair Value Measurement [Member]
Assets [Abstract]
Derivative instruments, assets	7.8	[1]	6.7	[1]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	18.4		18.7
Total assets	26.2		25.4
Liabilities [Abstract]
Derivative instruments, liabilities	0	[1]	0.1	[1]
Total liabilities	0		0.1
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Estimate of Fair Value Measurement [Member] | Equity Securities [Member]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0.1		0.1
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Estimate of Fair Value Measurement [Member] | Fixed Income Funds [Member]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	18.3		18.6
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Netting [Member]
Assets [Abstract]
Derivative instruments, assets	(1.0)	[1],[5]	(0.6)	[1],[5]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0	[5]	0	[5]
Total assets	(1.0)	[5]	(0.6)	[5]
Liabilities [Abstract]
Derivative instruments, liabilities	(1.0)	[1],[5]	(0.6)	[1],[5]
Total liabilities	(1.0)	[5]	(0.6)	[5]
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Netting [Member] | Equity Securities [Member]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Netting [Member] | Fixed Income Funds [Member]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative instruments, assets	0.5	[1]	0.2	[1]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0.1		0.1
Total assets	0.6		0.3
Liabilities [Abstract]
Derivative instruments, liabilities	0.3	[1]	0.6	[1]
Total liabilities	0.3		0.6
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0.1		0.1
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 1 [Member] | Fixed Income Funds [Member]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Derivative instruments, assets	4.6	[1]	4.9	[1]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	18.3		18.6
Total assets	22.9		23.5
Liabilities [Abstract]
Derivative instruments, liabilities	0	[1]	0.1	[1]
Total liabilities	0		0.1
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Income Funds [Member]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	18.3		18.6
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets	3.7	[1]	2.2	[1]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0		0
Total assets	3.7		2.2
Liabilities [Abstract]
Derivative instruments, liabilities	0.7	[1]	0	[1]
Total liabilities	0.7		0
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Income Funds [Member]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	$ 0		$ 0

[1] The fair value of derivative instruments is estimated using market quotes, over-the-counter forward price and volatility curves and correlations among fuel prices, net of estimated credit risk. Derivative instruments classified as Level 1 represent exchange traded derivative instruments. Derivative instruments classified as Level 2 represent non-exchange traded derivative instruments traded in over-the-counter markets. Derivative instruments classified as Level 3 represent non-exchange traded derivatives traded in over-the-counter markets for which observable market data is not available to corroborate the valuation inputs and TCRs valued at the most recent auction price in the SPP Integrated Marketplace.

[2] Fair value is based on quoted market prices of the investments held by the fund and/or valuation models.

[3] Fair value is based on quoted market prices of the investments held by the trust. Debt securities classified as Level 1 are comprised of U.S. Treasury securities. Debt securities classified as Level 2 are comprised of corporate bonds, U.S. Agency, state and local obligations, and other asset-backed securities.

[4] Fair value is based on quoted market prices and/or valuation models for equity securities and Net Asset Value (NAV) per share for fixed income funds.

[5] Represents the difference between derivative contracts in an asset or liability position presented on a net basis by counterparty on the consolidated balance sheets where a master netting agreement exists between the Company and the counterparty. At March 31, 2014, and December 31, 2013, Great Plains Energy netted $0.3 million and $0.2 million, respectively, of cash collateral posted with counterparties.