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The value recorded in accumulated other comprehensive income.

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Loss recorded in other comprehensive income on Forward Starting Swaps settled simultaneously with the issuance of long-term fixed rate debt.

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Percentage of expected on-peak natural gas and natural gas equivalent purchased power price exposure that is hedged at GMO

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Percentage of projected natural gas usage hedged at KCPL (in hundredths)

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Total monetary amount specified by the derivative(s). Expressed as an absolute value.

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The estimated net amount of existing gains (losses) on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 45

-Subparagraph b(2)

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Fair value of a derivative asset (or nonderivative instrument) that is designated and qualifies as a hedging instrument, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 205G

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-Subparagraph a

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FIN39-1

-Paragraph 10B

-Subparagraph a

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 205H

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

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-Name Statement of Financial Accounting Standard (FAS)

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DERIVATIVE INSTRUMENTS (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended	12 Months Ended			3 Months Ended		9 Months Ended				9 Months Ended								3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended													9 Months Ended								3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2011 Kansas City Power & Light Company [Member]	Sep. 30, 2010 Kansas City Power & Light Company [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member]	Sep. 30, 2010 Kansas City Power & Light Company [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Futures contracts [Member] Cash flow hedges [Member]	Dec. 31, 2010 Kansas City Power & Light Company [Member] Futures contracts [Member] Cash flow hedges [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Cash flow hedges [Member]	Dec. 31, 2010 Kansas City Power & Light Company [Member] Cash flow hedges [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Cash flow hedges [Member] Assets, current [Member]	Dec. 31, 2010 Kansas City Power & Light Company [Member] Cash flow hedges [Member] Assets, current [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Cash flow hedges [Member] Liabilities, current [Member]	Dec. 31, 2010 Kansas City Power & Light Company [Member] Cash flow hedges [Member] Liabilities, current [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Cash flow hedges [Member] Deferred income taxes [Member]	Dec. 31, 2010 Kansas City Power & Light Company [Member] Cash flow hedges [Member] Deferred income taxes [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Interest Rate Contract [Member]	Sep. 30, 2010 Kansas City Power & Light Company [Member] Interest Rate Contract [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Interest Rate Contract [Member]	Sep. 30, 2010 Kansas City Power & Light Company [Member] Interest Rate Contract [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Interest Rate Contract [Member] Interest charges [Member]	Sep. 30, 2010 Kansas City Power & Light Company [Member] Interest Rate Contract [Member] Interest charges [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Interest Rate Contract [Member] Interest charges [Member]	Sep. 30, 2010 Kansas City Power & Light Company [Member] Interest Rate Contract [Member] Interest charges [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Commodity Contract [Member]	Sep. 30, 2010 Kansas City Power & Light Company [Member] Commodity Contract [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Commodity Contract [Member]	Sep. 30, 2010 Kansas City Power & Light Company [Member] Commodity Contract [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Commodity Contract [Member] Fuel [Member]	Sep. 30, 2010 Kansas City Power & Light Company [Member] Commodity Contract [Member] Fuel [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Commodity Contract [Member] Fuel [Member]	Sep. 30, 2010 Kansas City Power & Light Company [Member] Commodity Contract [Member] Fuel [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Income Tax Benefit Expense [Member]	Sep. 30, 2010 Kansas City Power & Light Company [Member] Income Tax Benefit Expense [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Income Tax Benefit Expense [Member]	Sep. 30, 2010 Kansas City Power & Light Company [Member] Income Tax Benefit Expense [Member]	Sep. 30, 2011 Kansas City Power & Light Company [Member] Commodity Contract [Member] Derivative Instrument, Current and Noncurrent [Member]	Dec. 31, 2010 Kansas City Power & Light Company [Member] Commodity Contract [Member] Derivative Instrument, Current and Noncurrent [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member]	Sep. 30, 2010 Total (Great Plains Energy) [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member]	Sep. 30, 2010 Total (Great Plains Energy) [Member]	Dec. 31, 2010 Total (Great Plains Energy) [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Futures contracts [Member] Cash flow hedges [Member]	Dec. 31, 2010 Total (Great Plains Energy) [Member] Futures contracts [Member] Cash flow hedges [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Futures contracts [Member] Non-hedging derivatives	Dec. 31, 2010 Total (Great Plains Energy) [Member] Futures contracts [Member] Non-hedging derivatives	Sep. 30, 2011 Total (Great Plains Energy) [Member] Option contracts [Member] Non-hedging derivatives	Dec. 31, 2010 Total (Great Plains Energy) [Member] Option contracts [Member] Non-hedging derivatives	Sep. 30, 2011 Total (Great Plains Energy) [Member] Forward contracts [Member] Non-hedging derivatives	Dec. 31, 2010 Total (Great Plains Energy) [Member] Forward contracts [Member] Non-hedging derivatives	Sep. 30, 2011 Total (Great Plains Energy) [Member] Anticipated debt issuance [Member] Forward Starting Swaps [Member]	Dec. 31, 2010 Total (Great Plains Energy) [Member] Anticipated debt issuance [Member] Forward Starting Swaps [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Cash flow hedges [Member]	Dec. 31, 2010 Total (Great Plains Energy) [Member] Cash flow hedges [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Cash flow hedges [Member] Assets, current [Member]	Dec. 31, 2010 Total (Great Plains Energy) [Member] Cash flow hedges [Member] Assets, current [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Cash flow hedges [Member] Liabilities, current [Member]	Dec. 31, 2010 Total (Great Plains Energy) [Member] Cash flow hedges [Member] Liabilities, current [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Cash flow hedges [Member] Deferred income taxes [Member]	Dec. 31, 2010 Total (Great Plains Energy) [Member] Cash flow hedges [Member] Deferred income taxes [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Interest Rate Contract [Member]	Sep. 30, 2010 Total (Great Plains Energy) [Member] Interest Rate Contract [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Interest Rate Contract [Member]	Sep. 30, 2010 Total (Great Plains Energy) [Member] Interest Rate Contract [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Interest Rate Contract [Member] Interest charges [Member]	Sep. 30, 2010 Total (Great Plains Energy) [Member] Interest Rate Contract [Member] Interest charges [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Interest Rate Contract [Member] Interest charges [Member]	Sep. 30, 2010 Total (Great Plains Energy) [Member] Interest Rate Contract [Member] Interest charges [Member]	Dec. 31, 2010 Total (Great Plains Energy) [Member] Interest Rate Contract [Member] Derivative Instrument, Current and Noncurrent [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Commodity Contract [Member]	Sep. 30, 2010 Total (Great Plains Energy) [Member] Commodity Contract [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Commodity Contract [Member]	Sep. 30, 2010 Total (Great Plains Energy) [Member] Commodity Contract [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Commodity Contract [Member] Fuel [Member]	Sep. 30, 2010 Total (Great Plains Energy) [Member] Commodity Contract [Member] Fuel [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Commodity Contract [Member] Fuel [Member]	Sep. 30, 2010 Total (Great Plains Energy) [Member] Commodity Contract [Member] Fuel [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Income Tax Benefit Expense [Member]	Sep. 30, 2010 Total (Great Plains Energy) [Member] Income Tax Benefit Expense [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Income Tax Benefit Expense [Member]	Sep. 30, 2010 Total (Great Plains Energy) [Member] Income Tax Benefit Expense [Member]	Sep. 30, 2011 Total (Great Plains Energy) [Member] Commodity Contract [Member] Derivative Instrument, Current and Noncurrent [Member]	Dec. 31, 2010 Total (Great Plains Energy) [Member] Commodity Contract [Member] Derivative Instrument, Current and Noncurrent [Member]	Sep. 30, 2011 Commodity contract derivatives not designated as hedging instruments [Member]	Sep. 30, 2010 Commodity contract derivatives not designated as hedging instruments [Member]	Sep. 30, 2011 Commodity contract derivatives not designated as hedging instruments [Member]
Interest rate risk management [Line Items]
Amount of long term debt issued		$ 350.0
Number of Forward Starting Swaps settled with debt issued (in number of forward starting swaps)	6	6
Loss recorded in other comprehensive income on Forward Starting Swaps settled with debt issued		26.1
Reclassification period for loss recorded in other comprehensive income (years)	3	3
Amount of loss reclassified from other comprehensive income to interest expense	2.2	3.3
Commodity risk management [Abstract]
Percentage of projected natural gas usage hedged at KCPL (in hundredths)			91.00%	100.00%
Percentage of expected on-peak natural gas and natural gas equivalent purchased power price exposure that is hedged at GMO			50.00%	70.00%	68.00%
Derivative [Line Items]
Notional Contract Amount										2.6	4.0																																				2.6	4.0	20.2	59.5	0.4	0.2	135.4	202.8	0	350.0
Fair Value										(0.2)	0																																				(0.2)	0	(2.0)	(2.5)	0	0	9.3	8.9	0	(20.8)
Derivative Asset, Fair Value [Abstract]
Derivative Asset Designated as Hedging Instrument, Fair Value																																								0	0.1																																0													0	0.1
Derivative Asset Not Designated as Hedging Instrument, Fair Value																																																																																						9.3	9.4
Derivative Asset, Fair Value, Total																																										9.3		9.3		9.5
Derivative Liability, Fair Value [Abstract]
Derivative Liability Designated as Hedging Instrument, Fair Value																																								0.2	0.1																																20.8													0.2	0.1
Derivative Liability Not Designated as Hedging Instrument, Fair Value																																																																																						2.0	3.0
Derivative Liability, Fair Value, Total																																										2.2		2.2		23.9
Derivative Instruments, Gain (Loss) [Line Items]
Gain(Loss) Reclassified from Accumulated OCI into Income (Effective Portion)						(1.3)	(1.6)	(4.0)	(4.3)															(2.1)	(2.2)	(6.5)	(6.6)					(0.1)	(0.5)	(0.1)	(0.5)	0.9	1.1	2.6	2.8			(3.1)	(2.0)	(7.3)	(4.8)																								(5.1)	(2.6)	(11.9)	(7.2)						(0.1)	(0.5)	(0.1)	(0.5)	2.1	1.1	4.7	2.9
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)						0	(0.2)	(0.1)	(0.6)											0	0	0	0					(0.1)	(0.4)	(0.2)	(1.0)					0.1	0.2	0.1	0.4			0	(6.3)	(3.3)	(19.8)																				0	(9.9)	(5.3)	(31.4)						(0.1)	(0.4)	(0.2)	(1.0)					0.1	4.0	2.2	12.6
Gain(Loss) Reclassified from Regulatory Account into Income (Effective Portion)																																										(0.6)	(1.6)	(3.5)	(5.9)																																	(0.6)	(1.6)	(3.5)	(5.9)
Amount of Gain (Loss) Recognized on Regulatory Account on Derivatives (Effective Portion)																																										(2.2)	(2.8)	(3.5)	(8.7)																													(2.2)	(2.8)	(3.5)	(8.7)
Derivatives included in accumulated other comprehensive income recorded value [Line Items]
Recorded amount included in accumulated other comprehensive income												(32.5)	(36.4)	11.5	12.0	(64.7)	(71.6)	20.7	23.2																																						(50.7)	(54.7)	11.5	12.0	(94.5)	(101.5)	32.3	34.8
Accumulated other comprehensive income that is expected to be reclassified in the next twelve months												8.9																																													20.3
Trading Activity, Gains and Losses, Net [Line Items]
Gains (losses) reflected in the income statement for changes in fair value of commodity contracts not designated as hedging																																																																																								$ (0.6)	$ (1.6)	$ 0.4