Great Plains Energy (GXP) 10-Q 7 Nov 13 2013 Q3 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information (USD $)	9 Months Ended
	Sep. 30, 2013	Nov. 04, 2013	Jun. 30, 2012
Entity information [Abstract]	'	'	'
Entity Registrant Name	'Great Plains Energy Inc	'	'
Entity Central Index Key	'0001143068	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Well-known Seasoned Issuer	'Yes	'	'
Entity Voluntary Filers	'No	'	'
Entity Current Reporting Status	'Yes	'	'
Entity Filer Category	'Large Accelerated Filer	'	'
Entity Public Float	'	'	$3,273,153,264
Entity Common Stock, Shares Outstanding	'	153,825,245	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'Q3	'	'
Document Type	'10-Q	'	'
Amendment Flag	'false	'	'
Document Period End Date	30-Sep-13	'	'

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Sep. 30, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Current Assets	'		'
Cash and cash equivalents	$10.90		$9.30
Funds on deposit	1.2		1
Receivables, net	199.1		154.5
Accounts receivable pledged as collateral	190		174
Fuel inventories, at average cost	83.9		95.1
Materials and supplies, at average cost	155.6		151.3
Deferred refueling outage costs	33.7		11.9
Refundable income taxes	8.5		9.5
Deferred income taxes	50.9		88.5
Derivative instruments	1.4		1
Prepaid expenses and other assets	26.6		27.6
Assets, Current, Total	761.8		723.7
Utility Plant, at Original Cost	'		'
Electric	11,480.70		11,160.50
Less-accumulated depreciation	4,581.70		4,424.20
Net utility plant in service	6,899		6,736.30
Construction work in progress	684.7		584.5
Nuclear Fuel, Net of Amortization	69.6		81.3
Public Utilities, Property, Plant and Equipment, Net	7,653.30		7,402.10
Investments and Other Assets	'		'
Nuclear decommissioning trust fund	172.8		154.7
Regulatory Assets	1,032.20		1,120.90
Goodwill	169		169
Derivative instruments	4.5		5.5
Other Assets, Noncurrent	75.6		71.4
Investments and Other Assets, Total	1,454.10		1,521.50
Assets, Total	9,869.20		9,647.30
Current Liabilities	'		'
Notes payable	6		12
Collateralized note payable	190		174
Commercial paper	53		530.1
Current maturities of long-term debt	7.1		263.1
Accounts payable	199.4		330.2
Accrued taxes	106.3		27.1
Accrued interest	59.9		41.5
Accrued compensation and benefits	41.7		44.8
Pension and post-retirement liability	2.8		2.8
Other Liabilities, Current	23.1		23.9
Liabilities, Current, Total	689.3		1,449.50
Deferred Credits and Other Liabilities	'		'
Deferred income taxes	926.8		832.4
Deferred tax credits	127.8		128.8
Asset retirement obligations	156.4		149.3
Pension and post-retirement liability	554.6		557.5
Regulatory Liabilities	254.1		283.8
Other Liabilities, Noncurrent	118.4		110.2
Liabilities, Noncurrent, Total	2,138.10		2,062
Common shareholders' equity	'		'
Common Stock, Value, Issued	2,629.30		2,624.70
Retained earnings	889.8		758.8
Treasury Stock, Value	-2.9		-5.1
Accumulated other comprehensive loss	-29.2	[1]	-38.4	[1]
Common Shareholders' Equity, Total	3,487		3,340
Cumulative preferred stock $100 par value	'		'
Preferred Stock, Value, Issued	39		39
Long-term debt	3,515.80		2,756.80
Total Capitalization	7,041.80		6,135.80
Commitments and Contingencies	'		'
Liabilities and Equity, Total	9,869.20		9,647.30
Preferred Stock 3 Point 80 [Member]	'		'
Cumulative preferred stock $100 par value	'		'
Preferred Stock, Value, Issued	10		10
Preferred Stock 4 Point 50 [Member]	'		'
Cumulative preferred stock $100 par value	'		'
Preferred Stock, Value, Issued	10		10
Preferred Stock 4 Point 20 [Member]	'		'
Cumulative preferred stock $100 par value	'		'
Preferred Stock, Value, Issued	7		7
Preferred Stock 4 Point 35 [Member]	'		'
Cumulative preferred stock $100 par value	'		'
Preferred Stock, Value, Issued	12		12
Kansas City Power and Light Company [Member]	'		'
Current Assets	'		'
Cash and cash equivalents	3.5		5.2
Funds on deposit	0.5		0.1
Receivables, net	207.3		163.2
Accounts receivable pledged as collateral	110		110
Fuel inventories, at average cost	53.2		63.6
Materials and supplies, at average cost	113.1		110.1
Deferred refueling outage costs	33.7		11.9
Refundable income taxes	4.7		9.1
Deferred income taxes	0		4.6
Prepaid expenses and other assets	24.4		23.8
Assets, Current, Total	550.4		501.6
Utility Plant, at Original Cost	'		'
Electric	8,198.80		7,971.40
Less-accumulated depreciation	3,483.10		3,374.40
Net utility plant in service	4,715.70		4,597
Construction work in progress	588.1		486.5
Nuclear Fuel, Net of Amortization	69.6		81.3
Public Utilities, Property, Plant and Equipment, Net	5,373.40		5,164.80
Investments and Other Assets	'		'
Nuclear decommissioning trust fund	172.8		154.7
Regulatory Assets	799.1		853.2
Other Assets, Noncurrent	33.1		29.5
Investments and Other Assets, Total	1,005		1,037.40
Assets, Total	6,928.80		6,703.80
Current Liabilities	'		'
Collateralized note payable	110		110
Commercial paper	23.7		361
Current maturities of long-term debt	0		0.4
Accounts payable	156.8		254
Accrued taxes	72.3		21.9
Accrued interest	39.9		27.7
Accrued compensation and benefits	41.7		44.8
Pension and post-retirement liability	1.4		1.4
Deferred income taxes	2.8		0
Other Liabilities, Current	12.8		12.8
Liabilities, Current, Total	461.4		834
Deferred Credits and Other Liabilities	'		'
Deferred income taxes	920.7		836.4
Deferred tax credits	125.6		126.1
Asset retirement obligations	139.5		133.2
Pension and post-retirement liability	531.9		534.5
Regulatory Liabilities	160.7		153
Other Liabilities, Noncurrent	88.2		88.2
Liabilities, Noncurrent, Total	1,966.60		1,871.40
Common shareholders' equity	'		'
Common Stock, Value, Issued	1,563.10		1,563.10
Retained earnings	647.2		559.4
Accumulated other comprehensive loss	-21.6		-25.8
Common Shareholders' Equity, Total	2,188.70		2,096.70
Cumulative preferred stock $100 par value	'		'
Long-term debt	2,312.10		1,901.70
Total Capitalization	4,500.80		3,998.40
Commitments and Contingencies	'		'
Liabilities and Equity, Total	$6,928.80		$6,703.80
[1]	Net of tax

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	9 Months Ended	12 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Utility Plant, at Original Cost	'	'
Nuclear fuel, amortization	$153.90	$157.40
Common shareholder's equity	'	'
Common stock - shares authorized (in shares)	250,000,000	250,000,000
Common stock-shares issued (in shares)	153,948,017	153,779,806
Treasury stock- shares (in shares)	135,362	250,236
Preferred Stock 3 Point 80 [Member]	'	'
Cumulative preferred stock	'	'
Cumulative preferred stock par value (in dollars per share)	$100	$100
Cumulative preferred stock, Shares issued (in share)	100,000	100,000
Preferred Stock, Dividend Rate, Percentage	3.80%	3.80%
Preferred Stock 4 Point 50 [Member]	'	'
Cumulative preferred stock	'	'
Cumulative preferred stock par value (in dollars per share)	$100	$100
Cumulative preferred stock, Shares issued (in share)	100,000	100,000
Preferred Stock, Dividend Rate, Percentage	4.50%	4.50%
Preferred Stock 4 Point 20 [Member]	'	'
Cumulative preferred stock	'	'
Cumulative preferred stock par value (in dollars per share)	$100	$100
Cumulative preferred stock, Shares issued (in share)	70,000	70,000
Preferred Stock, Dividend Rate, Percentage	4.20%	4.20%
Preferred Stock 4 Point 35 [Member]	'	'
Cumulative preferred stock	'	'
Cumulative preferred stock par value (in dollars per share)	$100	$100
Cumulative preferred stock, Shares issued (in share)	120,000	120,000
Preferred Stock, Dividend Rate, Percentage	4.35%	4.35%
Kansas City Power and Light Company [Member]	'	'
Utility Plant, at Original Cost	'	'
Nuclear fuel, amortization	$153.90	$157.40
Common shareholder's equity	'	'
Common stock - shares authorized (in shares)	1,000	1,000
Common stock-shares issued (in shares)	1	1

Consolidated_Statements_of_Inc

Consolidated Statements of Income and Comprehensive Income (USD $)	3 Months Ended		9 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012
Operating Revenues	'	'	'		'
Electric revenues	$765	$746.20	$1,907.50		$1,829.50
Operating Expenses	'	'	'		'
Fuel	156.6	164.7	410		422.1
Purchased power	25.7	17.9	99.4		69.5
Transmission of electricity by others	13.6	9.8	37.9		25.9
Utility operating and maintenance expenses	170.2	156.8	491.8		484
Depreciation and amortization	73.3	68.9	216.1		204.2
General taxes	53.4	50.8	149.3		140.3
Other General and Administrative Expense	0.5	0.3	1.6		7.5
Costs and Expenses, Total	493.3	469.2	1,406.10		1,353.50
Operating Income (Loss)	271.7	277	501.4		476
Non-operating income	4.4	2.1	11.3		4.6
Non-operating expenses	-2.1	-1.9	-5.6		-9.5
Interest charges	-48.9	-48.1	-148		-170.8
Income before income tax (expense) benefit and income (loss) from equity investments	225.1	229.1	359.1		300.3
Income tax (expense) benefit	-81.8	-82.6	-126		-104.9
Income (loss) from equity investments, net of income taxes	-0.2	-0.1	-0.4		-0.2
Net income (loss)	143.1	146.4	232.7		195.2
Less: Net (income) loss attributable to noncontrolling interest	0	-0.2	0		0
Net income (loss) attributable to Great Plains Energy	143.1	146.2	232.7		195.2
Preferred stock dividend requirements	0.4	0.4	1.2		1.2
Earnings (loss) available for common shareholders	142.7	145.8	231.5		194
Average number of common shares outstanding (in shares)	153.6	153.2	153.5		142.9
Average number of diluted common shares outstanding (in shares)	153.8	153.4	153.7		145
Basic earnings (loss) per common share	'	'	'		'
Basic earnings per share	$0.93	$0.95	$1.51		$1.36
Diluted earnings (loss) per common share	'	'	'		'
Diluted earnings per share	$0.93	$0.95	$1.51		$1.34
Cash dividends per common share	$0.22	$0.21	$0.65		$0.64
Comprehensive Income	'	'	'		'
Net income (loss)	143.1	146.4	232.7		195.2
Other comprehensive income	'	'	'		'
Gain (loss) on derivative hedging instruments	0	0.1	0		-0.1
Income tax benefit (expense)	0	-0.1	0		0
Net gain (loss) on derivative hedging instruments	0	0	0		-0.1
Reclassification to expenses, net of tax	2.8	3.4	8.9		9.6
Derivative hedging activity, net of tax	2.8	3.4	8.9		9.5
Amortization of net losses included in net periodic benefit costs	0.1	0.1	0.4		0.3
Income tax benefit (expense)	0	0	-0.1		-0.1
Net change in unrecognized pension expense	0.1	0.1	0.3		0.2
Total other comprehensive income (loss)	2.9	3.5	9.2	[1]	9.7
Comprehensive income (loss)	146	149.9	241.9		204.9
Less: comprehensive (income) loss attributable to noncontrolling interest	0	-0.2	0		0
Comprehensive income (loss) attributable to Great Plains Energy	146	149.7	241.9		204.9
Kansas City Power and Light Company [Member]	'	'	'		'
Operating Revenues	'	'	'		'
Electric revenues	522	508	1,299.50		1,244.10
Operating Expenses	'	'	'		'
Fuel	111.5	114.5	292		297.8
Purchased power	10.9	10.1	48.6		23.7
Transmission of electricity by others	9.1	6.3	25.9		17.4
Utility operating and maintenance expenses	120.4	110.5	345.3		344.3
Depreciation and amortization	50.2	46.9	147.4		138.6
General taxes	43.1	41.9	117.8		113
Costs and Expenses, Total	345.2	330.2	977		934.8
Operating Income (Loss)	176.8	177.8	322.5		309.3
Non-operating income	4.8	1	10.3		2.3
Non-operating expenses	-1.1	-1.3	-2.7		-4.7
Interest charges	-31	-32.4	-94.5		-96.1
Income before income tax (expense) benefit and income (loss) from equity investments	149.5	145.1	235.6		210.8
Income tax (expense) benefit	-53.1	-54.9	-78.8		-74.6
Net income (loss)	96.4	90.2	156.8		136.2
Comprehensive Income	'	'	'		'
Net income (loss)	96.4	90.2	156.8		136.2
Other comprehensive income	'	'	'		'
Gain (loss) on derivative hedging instruments	0	0.1	0		-0.1
Income tax benefit (expense)	0	-0.1	0		0
Net gain (loss) on derivative hedging instruments	0	0	0		-0.1
Reclassification to expenses, net of tax	1.4	1.7	4.2		4.4
Derivative hedging activity, net of tax	1.4	1.7	4.2		4.3
Total other comprehensive income (loss)	1.4	1.7	4.2		4.3
Comprehensive income (loss) attributable to Great Plains Energy	$97.80	$91.90	$161		$140.50
[1]	Net of tax

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012
Cash Flows from Operating Activities	'		'
Net income (loss)	$232.70		$195.20
Adjustments to reconcile income to net cash from operating activities:	'		'
Depreciation and amortization	216.1		204.2
Amortization of:	'		'
Nuclear fuel	15.3		16.9
Other	43.4		22.6
Deferred income taxes, net	126.7		115.8
Investment tax credit amortization	-1.3		-1.8
Loss from equity investments, net of income taxes	0.4		0.2
Other operating activities	-50.1		-66.8
Net cash from operating activities	583.2		486.3
Cash Flows from Investing Activities	'		'
Utility capital expenditures	-486.2	[1]	-409.5
Allowance for borrowed funds used during construction	-8		-3.9
Purchases of nuclear decommissioning trust investments	-62.3		-20.4
Proceeds from nuclear decommissioning trust investments	59.8		17.9
Other investing activities	-15.1		-12.1
Net cash from investing activities	-511.8		-428
Cash Flows from Financing Activities	'		'
Issuance of common stock	3.8		291.6
Issuance of long-term debt	762.5		0
Issuance fees	-6.7		-2.6
Repayment of long-term debt	-259.3		-513.8
Net change in short-term borrowings	-483.1		169
Net change in collateralized short-term borrowings	16		95
Dividends paid	-101.5		-91.7
Other financing activities	-1.5		-5.1
Net cash from financing activities	-69.8		-57.6
Net Change in Cash and Cash Equivalents	1.6		0.7
Cash and Cash Equivalents at Beginning of Year	9.3		6.2
Cash and Cash Equivalents at End of Period	10.9		6.9
Kansas City Power and Light Company [Member]	'		'
Cash Flows from Operating Activities	'		'
Net income (loss)	156.8		136.2
Adjustments to reconcile income to net cash from operating activities:	'		'
Depreciation and amortization	147.4		138.6
Amortization of:	'		'
Nuclear fuel	15.3		16.9
Other	25.7		23.1
Deferred income taxes, net	91.5		47.4
Investment tax credit amortization	-0.8		-1.4
Other operating activities	-38.8		23.4
Net cash from operating activities	397.1		384.2
Cash Flows from Investing Activities	'		'
Utility capital expenditures	-375.8		-324.5
Allowance for borrowed funds used during construction	-7.1		-2.3
Purchases of nuclear decommissioning trust investments	-62.3		-20.4
Proceeds from nuclear decommissioning trust investments	59.8		17.9
Other investing activities	-8.6		-8.2
Net cash from investing activities	-394		-337.5
Cash Flows from Financing Activities	'		'
Issuance of long-term debt	412.5		0
Issuance fees	-4.6		0
Repayment of long-term debt	-2.6		-12.7
Net change in short-term borrowings	-337.3		29
Net change in collateralized short-term borrowings	0		15
Net money pool borrowings	-3.8		-4.2
Dividends paid	-69		-73
Other financing activities	0		0.1
Net cash from financing activities	-4.8		-45.8
Net Change in Cash and Cash Equivalents	-1.7		0.9
Cash and Cash Equivalents at Beginning of Year	5.2		1.9
Cash and Cash Equivalents at End of Period	$3.50		$2.80
[1]	Capital expenditures reflect year to date amounts for the periods presented.

Consolidated_Statements_of_Com

Consolidated Statements of Common Shareholders' Equity and Noncontrolling Interest (USD $)	Total	Kansas City Power and Light Company [Member]	Common Stock [Member]	Common Stock [Member]	Retained Earnings [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interest [Member]
In Millions, except Share data, unless otherwise specified				Kansas City Power and Light Company [Member]		Kansas City Power and Light Company [Member]			Kansas City Power and Light Company [Member]
Beginning balance at Dec. 31, 2011	'	'	$2,330.60	$1,563.10	$684.70	$513.80	($5.60)	($49.80)	($31.40)	$1
Beginning balance, treasury stock (in shares) at Dec. 31, 2011	'	'	'	'	'	'	-264,567	'	'	'
Beginning balance (in shares) at Dec. 31, 2011	'	'	136,406,306	1	'	'	'	'	'	'
Issuance of common stock	'	'	291.6	'	'	'	'	'	'	'
Issuance of common stock (in shares)	'	'	17,310,715	'	'	'	'	'	'	'
Equity compensation expense, net of forfeitures	'	'	0.2	'	'	'	'	'	'	'
Unearned Compensation [Abstract]	'	'	'	'	'	'	'	'	'	'
Issuance of restricted common stock	'	'	-3.2	'	'	'	'	'	'	'
Forfeiture of restricted common stock	'	'	1.3	'	'	'	'	'	'	'
Compensation expense recognized	'	'	1.9	'	'	'	'	'	'	'
Stockholders' Equity, Other	'	'	0.5	'	'	'	'	'	'	'
Net income (loss) attributable to Great Plains Energy	195.2	'	'	'	195.2	136.2	'	'	'	'
Loss on reissuance of treasury stock	'	'	'	'	-0.2	'	'	'	'	'
Dividends:	'	'	'	'	'	'	'	'	'	'
Common stock	'	'	'	'	-90.5	-73	'	'	'	'
Preferred stock - at required rates	'	'	'	'	-1.2	'	'	'	'	'
Performance shares	'	'	'	'	-0.2	'	'	'	'	'
Treasury shares acquired	'	'	'	'	'	'	-3.3	'	'	'
Treasury shares acquired (in shares)	'	'	'	'	'	'	-164,454	'	'	'
Treasury shares reissued	'	'	'	'	'	'	3.7	'	'	'
Treasury shares reissued (in shares)	'	'	'	'	'	'	174,795	'	'	'
Derivative hedging activity, net of tax	9.5	4.3	'	'	'	'	'	9.5	4.3	'
Change in unrecognized pension expense, net of tax	0.2	'	'	'	'	'	'	0.2	'	'
Net income (loss) attributable to noncontrolling interest	0	'	'	'	'	'	'	'	'	'
Distribution	'	'	'	'	'	'	'	'	'	-1
Ending balance at Sep. 30, 2012	3,365.40	2,113	2,622.90	1,563.10	787.8	577	-5.2	-40.1	-27.1	0
Ending balance (in shares) at Sep. 30, 2012	'	'	153,717,021	1	'	'	'	'	'	'
Ending balance, treasury stock (in shares) at Sep. 30, 2012	'	'	'	'	'	'	-254,226	'	'	'
Beginning balance at Jun. 30, 2012	'	'	'	'	'	'	'	'	'	'
Unearned Compensation [Abstract]	'	'	'	'	'	'	'	'	'	'
Net income (loss) attributable to Great Plains Energy	146.2	'	'	'	'	'	'	'	'	'
Dividends:	'	'	'	'	'	'	'	'	'	'
Derivative hedging activity, net of tax	3.4	1.7	'	'	'	'	'	'	'	'
Change in unrecognized pension expense, net of tax	0.1	'	'	'	'	'	'	'	'	'
Net income (loss) attributable to noncontrolling interest	-0.2	'	'	'	'	'	'	'	'	'
Ending balance at Sep. 30, 2012	3,365.40	2,113	'	1,563.10	'	'	'	'	'	'
Ending balance (in shares) at Sep. 30, 2012	'	'	'	1	'	'	'	'	'	'
Beginning balance at Dec. 31, 2012	3,340	2,096.70	2,624.70	1,563.10	758.8	559.4	-5.1	-38.4	-25.8	0
Beginning balance, treasury stock (in shares) at Dec. 31, 2012	-250,236	'	'	'	'	'	-250,236	'	'	'
Beginning balance (in shares) at Dec. 31, 2012	'	'	153,779,806	1	'	'	'	'	'	'
Issuance of common stock	'	'	3.8	'	'	'	'	'	'	'
Issuance of common stock (in shares)	'	'	168,211	'	'	'	'	'	'	'
Equity compensation expense, net of forfeitures	'	'	0.3	'	'	'	'	'	'	'
Unearned Compensation [Abstract]	'	'	'	'	'	'	'	'	'	'
Issuance of restricted common stock	'	'	-1.7	'	'	'	'	'	'	'
Forfeiture of restricted common stock	'	'	0.1	'	'	'	'	'	'	'
Compensation expense recognized	'	'	1.5	'	'	'	'	'	'	'
Stockholders' Equity, Other	'	'	0.6	'	'	'	'	'	'	'
Net income (loss) attributable to Great Plains Energy	232.7	'	'	'	232.7	156.8	'	'	'	'
Loss on reissuance of treasury stock	'	'	'	'	0	'	'	'	'	'
Dividends:	'	'	'	'	'	'	'	'	'	'
Common stock	'	'	'	'	-100.3	-69	'	'	'	'
Preferred stock - at required rates	'	'	'	'	-1.2	'	'	'	'	'
Performance shares	'	'	'	'	-0.2	'	'	'	'	'
Treasury shares acquired	'	'	'	'	'	'	-1.6	'	'	'
Treasury shares acquired (in shares)	'	'	'	'	'	'	-73,201	'	'	'
Treasury shares reissued	'	'	'	'	'	'	3.8	'	'	'
Treasury shares reissued (in shares)	'	'	'	'	'	'	188,075	'	'	'
Derivative hedging activity, net of tax	8.9	4.2	'	'	'	'	'	8.9	4.2	'
Change in unrecognized pension expense, net of tax	0.3	'	'	'	'	'	'	0.3	'	'
Net income (loss) attributable to noncontrolling interest	0	'	'	'	'	'	'	'	'	'
Distribution	'	'	'	'	'	'	'	'	'	0
Ending balance at Sep. 30, 2013	3,487	2,188.70	2,629.30	1,563.10	889.8	647.2	-2.9	-29.2	-21.6	0
Ending balance (in shares) at Sep. 30, 2013	'	'	153,948,017	1	'	'	'	'	'	'
Ending balance, treasury stock (in shares) at Sep. 30, 2013	-135,362	'	'	'	'	'	-135,362	'	'	'
Beginning balance at Jun. 30, 2013	'	'	'	'	'	'	'	'	'	'
Unearned Compensation [Abstract]	'	'	'	'	'	'	'	'	'	'
Net income (loss) attributable to Great Plains Energy	143.1	'	'	'	'	'	'	'	'	'
Dividends:	'	'	'	'	'	'	'	'	'	'
Derivative hedging activity, net of tax	2.8	1.4	'	'	'	'	'	'	'	'
Change in unrecognized pension expense, net of tax	0.1	'	'	'	'	'	'	'	'	'
Net income (loss) attributable to noncontrolling interest	0	'	'	'	'	'	'	'	'	'
Ending balance at Sep. 30, 2013	$3,487	$2,188.70	'	$1,563.10	'	'	'	'	'	'
Ending balance (in shares) at Sep. 30, 2013	'	'	'	1	'	'	'	'	'	'
Ending balance, treasury stock (in shares) at Sep. 30, 2013	-135,362	'	'	'	'	'	'	'	'	'

Consolidated_Statements_of_Com1

Consolidated Statements of Common Shareholders' Equity and Noncontrolling Interest Consolidated Statements of Common Shareholders' Equity and Noncontrolling Interest (Parenthetical) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Stock Transactions, Parenthetical Disclosures [Abstract]	'	'	'	'
Common Stock, Dividends, Per Share, Declared	$0.22	$0.21	$0.65	$0.64

Summary_of_Significant_Account

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Summary of Significant Accounting Policies [Text Block]	'
	1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	Organization
	Great Plains Energy, a Missouri corporation incorporated in 2001, is a public utility holding company and does not own or operate any significant assets other than the stock of its subsidiaries.  Great Plains Energy's wholly owned direct subsidiaries with operations or active subsidiaries are as follows:
	•	KCP&L is an integrated, regulated electric utility that provides electricity to customers primarily in the states of Missouri and Kansas.  KCP&L has one active wholly owned subsidiary, Kansas City Power & Light Receivables Company (KCP&L Receivables Company).
	•	KCP&L Greater Missouri Operations Company (GMO) is an integrated, regulated electric utility that primarily provides electricity to customers in the state of Missouri.  GMO also provides regulated steam service to certain customers in the St. Joseph, Missouri area.  GMO has two active wholly owned subsidiaries, GMO Receivables Company and MPS Merchant Services, Inc. (MPS Merchant).  MPS Merchant has certain long-term natural gas contracts remaining from its former non-regulated trading operations.
	Each of Great Plains Energy's and KCP&L's consolidated financial statements includes the accounts of their subsidiaries.  Intercompany transactions have been eliminated.
	Great Plains Energy's sole reportable business segment is electric utility.  See Note 16 for additional information.
	Basic and Diluted Earnings per Common Share Calculation
	To determine basic EPS, preferred stock dividend requirements and net income attributable to noncontrolling interest are deducted from net income before dividing by the average number of common shares outstanding.  The effect of dilutive securities, calculated using the treasury stock method, assumes the issuance of common shares applicable to performance shares, restricted stock and Equity Units. Great Plains Energy settled the Equity Units in June 2012.
	The following table reconciles Great Plains Energy's basic and diluted EPS.
			Three Months Ended						Year to Date
			30-Sep						30-Sep
			2013			2012			2013		2012
	Income		(millions, except per share amounts)
	Net income		$	143.1		$	146.4		$	232.7	$	195.2
	Less: net income attributable to noncontrolling interest		—			0.2			—		—
	Less: preferred stock dividend requirements		0.4			0.4			1.2		1.2
	Earnings available for common shareholders		$	142.7		$	145.8		$	231.5	$	194
	Common Shares Outstanding
	Average number of common shares outstanding		153.6			153.2			153.5		142.9
	Add: effect of dilutive securities		0.2			0.2			0.2		2.1
	Diluted average number of common shares outstanding		153.8			153.4			153.7		145
	Basic EPS		$	0.93		$	0.95		$	1.51	$	1.36
	Diluted EPS		$	0.93		$	0.95		$	1.51	$	1.34
	Anti-dilutive shares excluded from the computation of diluted EPS are detailed in the following table.
			Three Months Ended					Year to Date
			30-Sep					30-Sep
			2013		2012			2013		2012
	Performance shares		54,660		192,723			54,660		209,000
	Restricted stock shares		—		2,531			21,652		2,531
	Dividends Declared
	In November 2013, Great Plains Energy's Board of Directors (Board) declared a quarterly dividend of $0.23 per share on Great Plains Energy's common stock.  The common dividend is payable December 20, 2013, to shareholders of record as of November 29, 2013.  The Board also declared regular dividends on Great Plains Energy's preferred stock, payable March 1, 2014, to shareholders of record as of February 7, 2014.
	In November 2013, KCP&L’s Board of Directors declared a cash dividend payable to Great Plains Energy of $23 million payable on December 19, 2013.

Supplemental_Cash_Flow_Informa

Supplemental Cash Flow Information	9 Months Ended
	Sep. 30, 2013
Supplemental Cash Flow Elements [Abstract]	'
Cash Flow, Supplemental Disclosures [Text Block]	'
	2. SUPPLEMENTAL CASH FLOW INFORMATION
	Great Plains Energy Other Operating Activities
	Year to Date September 30	2013			2012
	Cash flows affected by changes in:	(millions)
	Receivables	$	(44.1	)	$	12.5
	Accounts receivable pledged as collateral	(16.0		)	(95.0		)
	Fuel inventories	11.2			(5.4		)
	Materials and supplies	(4.3		)	(7.8		)
	Accounts payable	(91.5		)	(49.4		)
	Accrued taxes	81			65.4
	Accrued interest	18.4			(16.6		)
	Deferred refueling outage costs	(21.8		)	13.4
	Pension and post-retirement benefit obligations	40.2			21.9
	Allowance for equity funds used during construction	(9.1		)	(0.3		)
	Fuel recovery mechanism	(5.3		)	13.1
	Uncertain tax positions	(0.4		)	(4.4		)
	Other	(8.4		)	(14.2		)
	Total other operating activities	$	(50.1	)	$	(66.8	)
	Cash paid during the period:
	Interest	$	111.3		$	185.4
	Income taxes	$	0.1		$	3.3
	Non-cash investing activities:
	Liabilities accrued for capital expenditures	$	34.5		$	52.2
	KCP&L Other Operating Activities
	Year to Date September 30	2013			2012
	Cash flows affected by changes in:	(millions)
	Receivables	$	(40.2	)	$	(35.1	)
	Accounts receivable pledged as collateral	—			(15.0		)
	Fuel inventories	10.4			(6.2		)
	Materials and supplies	(3.0		)	(6.1		)
	Accounts payable	(66.7		)	(18.0		)
	Accrued taxes	55.3			76.5
	Accrued interest	12.2			9.8
	Deferred refueling outage costs	(21.8		)	13.4
	Pension and post-retirement benefit obligations	41.9			24.7
	Allowance for equity funds used during construction	(9.1		)	(0.3		)
	Fuel recovery mechanism	(1.2		)	(0.9		)
	Uncertain tax positions	(10.5		)	1.2
	Other	(6.1		)	(20.6		)
	Total other operating activities	$	(38.8	)	$	23.4
	Cash paid during the period:
	Interest	$	73.2		$	77.3
	Income taxes	$	—		$	—
	Non-cash investing activities:
	Liabilities accrued for capital expenditures	$	28.3		$	48

Receivables

Receivables	9 Months Ended
	Sep. 30, 2013
Receivables [Abstract]	'
Receivables [Text Block]	'
	3. RECEIVABLES
	Great Plains Energy's and KCP&L's receivables are detailed in the following table.
		September 30				December 31
			2013				2012
	Great Plains Energy		(millions)
	Customer accounts receivable - billed		$	24.4			$	—
	Customer accounts receivable - unbilled		89.7				58.3
	Allowance for doubtful accounts - customer accounts receivable		(3.4		)		(2.6		)
	Other receivables		88.4				98.8
	Total		$	199.1			$	154.5
	KCP&L
	Customer accounts receivable - billed		$	23.8			$	—
	Customer accounts receivable - unbilled		64.7				42.9
	Allowance for doubtful accounts - customer accounts receivable		(1.9		)		(1.5		)
	Intercompany receivables		40.4				40
	Other receivables		80.3				81.8
	Total		$	207.3			$	163.2
	Great Plains Energy's and KCP&L's other receivables at September 30, 2013, and December 31, 2012, consisted primarily of receivables from partners in jointly owned electric utility plants and wholesale sales receivables.
	Sale of Accounts Receivable – KCP&L and GMO
	KCP&L and GMO sell all of their retail electric and steam service accounts receivable to their wholly owned subsidiaries, KCP&L Receivables Company and GMO Receivables Company, respectively, which in turn sell an undivided percentage ownership interest in the accounts receivable to Victory Receivables Corporation, an independent outside investor.  Each of KCP&L Receivables Company's and GMO Receivables Company's sale of the undivided percentage ownership interest in accounts receivable to Victory Receivables Corporation is accounted for as a secured borrowing with accounts receivable pledged as collateral and a corresponding short-term collateralized note payable recognized on the balance sheets.  At September 30, 2013, and December 31, 2012, Great Plains Energy's accounts receivable pledged as collateral and the corresponding short-term collateralized note payable were $190.0 million and $174.0 million, respectively.  At September 30, 2013, and December 31, 2012, KCP&L's accounts receivable pledged as collateral and the corresponding short-term collateralized note payable were $110.0 million.
	KCP&L and GMO each sell their receivables at a fixed price based upon the expected cost of funds and charge-offs.  These costs comprise KCP&L's and GMO's loss on the sale of accounts receivable.  KCP&L and GMO service the receivables and receive annual servicing fees of 1.5% and 1.25%, respectively, of the outstanding principal amount of the receivables sold to KCP&L Receivables Company and GMO Receivables Company. KCP&L and GMO do not recognize a servicing asset or liability because management determined the collection agent fees earned by KCP&L and GMO approximate market value.  KCP&L's agreement expires in September 2014 and allows for $110 million in aggregate outstanding principal amount at any time.  GMO's agreement expires in September 2014 and allows for $80 million in aggregate outstanding principal during the period of June 1 through October 31 and $65 million in aggregate outstanding principal during the period of November 1 through May 31 of each year.
	Information regarding KCP&L's sale of accounts receivable to KCP&L Receivables Company and GMO's sale of accounts receivable to GMO Receivables Company is reflected in the following tables.
	Three Months Ended	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
	30-Sep-13					Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(481.2	)		$	481.2			$	—			$	(264.1	)		$	264.1			$	—
	Gain (loss) on sale of accounts receivable (a)		(6.1		)		5.8				(0.3		)		(3.4		)		3.2				(0.5		)
	Servicing fees received (paid)		0.8				(0.8		)		—				0.4				(0.4		)		—
	Fees paid to outside investor		—				(0.3		)		(0.3		)		—				(0.2		)		(0.5		)
	Cash from customers (transferred) received		(468.5		)		468.5				—				(260.5		)		260.5				—
	Cash received from (paid for) receivables purchased		462.6				(462.6		)		—				257.2				(257.2		)		—
	Interest on intercompany note received (paid)		0.1				(0.1		)		—				0.1				(0.1		)		—
	Year to Date	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
	30-Sep-13					Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(1,189.2	)		$	1,189.20			$	—			$	(652.2	)		$	652.2			$	—
	Gain (loss) on sale of accounts receivable (a)		(15.1		)		14.4				(0.7		)		(8.3		)		7.9				(1.1		)
	Servicing fees received (paid)		2				(2.0		)		—				1				(1.0		)		—
	Fees paid to outside investor		—				(0.9		)		(0.9		)		—				(0.5		)		(1.4		)
	Cash from customers (transferred) received		(1,150.8		)		1,150.80				—				(630.0		)		630				—
	Cash received from (paid for) receivables purchased		1,136.40				(1,136.4		)		—				622.1				(622.1		)		—
	Interest on intercompany note received (paid)		0.2				(0.2		)		—				0.1				(0.1		)		—
	Three Months Ended	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
	30-Sep-12					Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(472.6	)		$	472.6			$	—			$	(341.7	)		$	341.7			$	—
	Gain (loss) on sale of accounts receivable (a)		(6.0		)		5.8				(0.2		)		(4.3		)		3.4				(1.1		)
	Servicing fees received (paid)		0.8				(0.8		)		—				0.5				(0.5		)		—
	Fees paid to outside investor		—				(0.3		)		(0.3		)		—				(0.3		)		(0.6		)
	Cash from customers (transferred) received		(466.1		)		466.1				—				(267.8		)		267.8				—
	Cash received from (paid for) receivables purchased		460.4				(460.4		)		—				264.4				(264.4		)		—
	Interest on intercompany note received (paid)		0.2				(0.2		)		—				0.1				(0.1		)		—
	Year to Date	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
	30-Sep-12					Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(1,134.7	)		$	1,134.70			$	—			$	(433.4	)		$	433.4			$	—
	Gain (loss) on sale of accounts receivable (a)		(14.4		)		13.9				(0.5		)		(5.5		)		4.2				(1.8		)
	Servicing fees received (paid)		1.9				(1.9		)		—				0.6				(0.6		)		—
	Fees paid to outside investor		—				(0.9		)		(0.9		)		—				(0.4		)		(1.3		)
Cash from customers (transferred) received		(1,112.7		)		1,112.70				—				(332.5		)		332.5				—
Cash received from (paid for) receivables purchased		1,098.80				(1,098.8		)		—				328.3				(328.3		)		—
Interest on intercompany note received (paid)		0.3				(0.3		)		—				0.1				(0.1		)		—
(a) Any net gain (loss) is the result of the timing difference inherent in collecting receivables and over the life of the agreement will net to zero.

Nuclear_Plant

Nuclear Plant	9 Months Ended
	Sep. 30, 2013
Nuclear Plant [Abstract]	'
Nuclear Plant	'
	4. NUCLEAR PLANT
	KCP&L owns 47% of Wolf Creek Generating Station (Wolf Creek), its only nuclear generating unit.  Wolf Creek is located in Coffey County, Kansas, just northeast of Burlington, Kansas.  Wolf Creek's operating license expires in 2045.  Wolf Creek is regulated by the Nuclear Regulatory Commission (NRC) with respect to licensing, operations and safety-related requirements.
	Spent Nuclear Fuel and High-Level Radioactive Waste
	Under the Nuclear Waste Policy Act of 1982, the Department of Energy (DOE) is responsible for the permanent disposal of spent nuclear fuel.  KCP&L pays the DOE a quarterly fee of one-tenth of a cent for each kWh of net nuclear generation delivered and sold for the future disposal of spent nuclear fuel.  These disposal costs are charged to fuel expense.  In 2010, the DOE filed a motion with the NRC to withdraw its then pending application to the NRC to construct a national repository for the disposal of spent nuclear fuel and high-level radioactive waste at Yucca Mountain, Nevada.  An NRC board denied the DOE's motion to withdraw its application, and the DOE appealed that decision to the full NRC.  In 2011, the NRC issued an evenly split decision on the appeal and ordered the licensing board to close out its work on the DOE's application due to a lack of funding.  In August 2013, a federal court of appeals ruled that the NRC must resume its review of the DOE's application.  Wolf Creek has an on-site storage facility designed to hold all spent fuel generated at the plant through 2025, and believes it will be able to expand on-site storage as needed past 2025.  Management cannot predict when, or if, an alternative disposal site will be available to receive Wolf Creek's spent nuclear fuel and will continue to monitor this activity.
	Low-Level Radioactive Waste
	Wolf Creek disposes of most of its low-level radioactive waste (Class A waste) at an existing third-party repository in Utah.  Management expects that the site located in Utah will remain available to Wolf Creek for disposal of its Class A waste.  Wolf Creek has contracted with a waste processor that will process, take title and dispose in another state most of the remainder of Wolf Creek's low-level radioactive waste (Classes B and C waste, which is higher in radioactivity but much lower in volume).  Should on-site waste storage be needed in the future, Wolf Creek has current storage capacity on site for about four years' generation of Classes B and C waste and believes it will be able to expand that storage capacity as needed if it becomes necessary to do so.
	Nuclear Decommissioning Trust Fund
	The following table summarizes the change in Great Plains Energy's and KCP&L's nuclear decommissioning trust fund.
		September 30					December 31
		2013					2012
	Decommissioning Trust		(millions)
	Beginning balance January 1		$	154.7				$	135.3
	Contributions		2.5					3.3
	Earned income, net of fees		1.9					3
	Net realized gains		1.6					1
	Net unrealized gains		12.1					12.1
	Ending balance		$	172.8				$	154.7
	The nuclear decommissioning trust is reported at fair value on the balance sheets and is invested in assets as detailed in the following table.
		September 30																		December 31
		2013																		2012
		Cost			Unrealized Gains						Unrealized					Fair			Cost			Unrealized			Unrealized				Fair
		Basis									Losses					Value			Basis			Gains			Losses				Value
		(millions)
	Equity securities	$	83.4			$	35.1					$	(1.0	)			$	117.5		$	80.6		$	21.1		$	(1.6	)		$	100.1
	Debt securities	49.8				2.8						(0.5		)			52.1			46.6			4.9			(0.1		)		51.4
	Other	3.2				—						—					3.2			3.2			—			—				3.2
	Total	$	136.4			$	37.9					$	(1.5	)			$	172.8		$	130.4		$	26		$	(1.7	)		$	154.7
	The weighted-average maturity of debt securities held by the trust at September 30, 2013, was approximately 7 years.  The costs of securities sold are determined on the basis of specific identification.  The following table summarizes the realized gains and losses from the sale of securities in the nuclear decommissioning trust fund.
		Three Months Ended							Year to Date
		30-Sep							30-Sep
		2013			2012				2013				2012
		(millions)
	Realized gains	$	0.4		$	0.5			$	2.3			$	1.2
	Realized losses	(0.3		)	(0.1		)		(0.7		)		(0.3		)

Pension_Plans_and_Other_Employ

Pension Plans and Other Employee Benefits	9 Months Ended
	Sep. 30, 2013
Compensation and Retirement Disclosure [Abstract]	'
Pension Plans and Other Employee Benefits	'
	5. PENSION PLANS AND OTHER EMPLOYEE BENEFITS
	Great Plains Energy maintains defined benefit pension plans for substantially all active and inactive employees, including officers, of KCP&L, GMO and Wolf Creek Nuclear Operating Corporation (WCNOC) and incurs significant costs in providing the plans.  Pension benefits under these plans reflect the employees' compensation, years of service and age at retirement.  In addition to providing pension benefits, Great Plains Energy provides certain post-retirement health care and life insurance benefits for substantially all retired employees of KCP&L, GMO and WCNOC.
	KCP&L and GMO record pension and post-retirement expense in accordance with rate orders from the Public Service Commission of the State of Missouri (MPSC) and The State Corporation Commission of the State of Kansas (KCC) that allow the difference between pension and post-retirement costs under Generally Accepted Accounting Principles (GAAP) and costs for ratemaking to be recognized as a regulatory asset or liability.  This difference between financial and regulatory accounting methods is due to timing and will be eliminated over the life of the plans.
	The following tables provide Great Plains Energy's components of net periodic benefit costs prior to the effects of capitalization and sharing with joint owners of power plants.
		Pension Benefits						Other Benefits
	Three Months Ended September 30	2013			2012			2013			2012
	Components of net periodic benefit costs	(millions)
	Service cost	$	10.5		$	8.9		$	1.1		$	0.8
	Interest cost	11.8			12.2			1.9			1.9
	Expected return on plan assets	(11.8		)	(10.7		)	(0.5		)	(0.4		)
	Prior service cost	0.5			1.1			1.8			1.8
	Recognized net actuarial loss	13.7			11.1			0.5			—
	Transition obligation	—			—			—			0.3
	Net periodic benefit costs before regulatory adjustment	24.7			22.6			4.8			4.4
	Regulatory adjustment	(3.3		)	(3.9		)	(0.6		)	0.3
	Net periodic benefit costs	$	21.4		$	18.7		$	4.2		$	4.7
		Pension Benefits						Other Benefits
	Year to Date September 30	2013			2012			2013			2012
	Components of net periodic benefit costs	(millions)
	Service cost	$	31.5		$	26.6		$	3.3		$	2.4
	Interest cost	35.4			36.7			5.7			5.8
	Expected return on plan assets	(35.4		)	(32.1		)	(1.5		)	(1.3		)
	Prior service cost	1.5			3.3			5.4			5.4
	Recognized net actuarial loss	41.1			33.4			1.4			—
	Transition obligation	—			—			0.1			0.8
	Net periodic benefit costs before regulatory adjustment	74.1			67.9			14.4			13.1
	Regulatory adjustment	(9.7		)	(11.6		)	(1.7		)	1
	Net periodic benefit costs	$	64.4		$	56.3		$	12.7		$	14.1
	Year to date September 30, 2013, Great Plains Energy contributed $40.2 million to the pension plans and expects to contribute an additional $17.2 million in 2013 to satisfy the minimum Employee Retirement Income Security Act of 1974, as amended (ERISA) funding requirements and the MPSC and KCC rate orders, the majority of which is expected to be paid by KCP&L. Also in 2013, Great Plains Energy expects to make contributions of $18.7 million to the post-retirement benefit plans, the majority of which is expected to be paid by KCP&L.

Equity_Compensation

Equity Compensation	9 Months Ended
	Sep. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Equity Compensation	'
	6. EQUITY COMPENSATION
	Great Plains Energy's Long-Term Incentive Plan is an equity compensation plan approved by Great Plains Energy's shareholders. The Long-Term Incentive Plan permits the grant of restricted stock, restricted stock units, bonus shares, stock options, stock appreciation rights, limited stock appreciation rights, director shares, director deferred share units and performance shares to directors, officers and other employees of Great Plains Energy and KCP&L. Forfeiture rates are based on historical forfeitures and future expectations and are reevaluated annually.
	The following table summarizes Great Plains Energy's and KCP&L's equity compensation expense and the associated income tax benefit.
			Three Months Ended					Year to Date
			30-Sep					30-Sep
			2013		2012			2013		2012
	Great Plains Energy		(millions)
	Equity compensation expense		$	1.3	$	1.2		$	3.4	$	4
	Income tax benefit		0.4		0.4			1.1		1.7
	KCP&L
	Equity compensation expense		$	0.9	$	0.8		$	2.4	$	2.9
	Income tax benefit		0.3		0.3			0.7		1.3
	Performance Shares
	Performance share activity is summarized in the following table. Performance adjustment represents the number of shares of common stock related to performance shares ultimately issued that can vary from the number of performance shares initially granted depending on Great Plains Energy's performance over a stated period of time.
		Performance			Grant Date
		Shares			Fair Value*
	Beginning balance January 1, 2013		370,560			$	23.05
	Granted		226,967			24.17
	Earned		(104,453	)		23.37
	Forfeited		(11,523	)		22.82
	Performance adjustment		(51,542	)		23.37
	Ending balance September 30, 2013		430,009			23.52
	* weighted-average
	At September 30, 2013, the remaining weighted-average contractual term was 1.6 years. The weighted-average grant-date fair value of shares granted was $24.33 and $24.17 for the three months ended and year to date September 30, 2013, respectively. The weighted-average grant-date fair value of shares granted was $18.12 and $19.02 for the three months ended and year to date September 30, 2012, respectively. At September 30, 2013, there was $4.3 million of total unrecognized compensation expense, net of forfeiture rates, related to performance shares granted under the Long-Term Incentive Plan, which will be recognized over the remaining weighted-average contractual term.  The total fair value of performance shares earned and paid year to date September 30, 2013, was $2.4 million. There were no performance shares earned and paid year to date September 30, 2012.
	The fair value of performance share awards is estimated using the market value of the Company's stock at the valuation date and a Monte Carlo simulation technique that incorporates assumptions for inputs of expected volatilities, dividend yield and risk-free rates. Expected volatility is based on daily stock price change during a historical period commensurate with the remaining term of the performance period of the grant. The risk-free rate is based upon the rate at the time of the evaluation for zero-coupon government bonds with a maturity consistent with the remaining performance period of the grant. The dividend yield is based on the most recent dividends paid and the actual closing stock price on the valuation date. For shares granted in 2013, inputs for expected volatility, dividend yield and risk-free rates were 19%, 3.88% and 0.35%, respectively.
	Restricted Stock
	Restricted stock activity is summarized in the following table.
		Nonvested			Grant Date
		Restricted Stock			Fair Value*
	Beginning balance January 1, 2013		277,439			$	19.03
	Granted and issued		75,745			22.46
	Vested		(64,405	)		17.88
	Forfeited		(4,142	)		21.44
	Ending balance September 30, 2013		284,637			20.14
	* weighted-average
	At September 30, 2013, the remaining weighted-average contractual term was 1.4 years.  The weighted-average grant-date fair value of shares granted was $22.65 and $22.46 for the three months ended and year to date September 30, 2013, respectively. The weighted-average grant-date fair value of shares granted was $22.18 and $19.73 for the three months ended and year to date September 30, 2012, respectively.  At September 30, 2013, there was $2.6 million of total unrecognized compensation expense, net of forfeiture rates, related to nonvested restricted stock granted under the Long-Term Incentive Plan, which will be recognized over the remaining weighted-average contractual term. The total fair value of shares vested was $0.6 million and $1.2 million for the three months ended and year to date September 30, 2013, respectively. The total fair value of shares vested was insignificant and $3.3 million for the three months ended and year to date September 30, 2012, respectively.

Shortterm_Borrowings_and_Short

Short-term Borrowings and Short-term Bank Lines of Credit	9 Months Ended
	Sep. 30, 2013
Short-term Borrowings and Short-term Bank Lines of Credit [Abstract]	'
Short-term Borrowings and Short-term Bank Lines of Credit [Text Block]	'
	7. SHORT-TERM BORROWINGS AND SHORT-TERM BANK LINES OF CREDIT
	Great Plains Energy's $200 Million Revolving Credit Facility
	In October 2013, Great Plains Energy entered into an amendment to its $200 million revolving credit facility with a group of banks to extend the term to October 2018 from December 2016.  The facility's terms permit transfers of unused commitments between this facility and the KCP&L and GMO facilities discussed below, with the total amount of the facility not exceeding $400 million at any one time.  A default by Great Plains Energy or any of its significant subsidiaries on other indebtedness totaling more than $50.0 million is a default under the facility.  Under the terms of this facility, Great Plains Energy is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times.  At September 30, 2013, Great Plains Energy was in compliance with this covenant.  At September 30, 2013, Great Plains Energy had $6.0 million of outstanding cash borrowings at a weighted-average interest rate of 1.94% and had issued letters of credit totaling $1.8 million under the credit facility.  At December 31, 2012, Great Plains Energy had $12.0 million of outstanding cash borrowings at a weighted-average interest rate of 2.00% and had issued letters of credit totaling $1.8 million under the credit facility.
	KCP&L's $600 Million Revolving Credit Facility and Commercial Paper
	In October 2013, KCP&L entered into an amendment to its $600 million revolving credit facility with a group of banks that provides support for its issuance of commercial paper and other general corporate purposes to extend the term to October 2018 from December 2016.  Great Plains Energy and KCP&L may transfer up to $200 million of unused commitments between Great Plains Energy's and KCP&L's facilities.  A default by KCP&L on other indebtedness totaling more than $50.0 million is a default under the facility.  Under the terms of this facility, KCP&L is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times.  At September 30, 2013, KCP&L was in compliance with this covenant.  At September 30, 2013, KCP&L had $23.7 million of commercial paper outstanding at a weighted-average interest rate of 0.27%, had issued letters of credit totaling $3.8 million and had no outstanding cash borrowings under the credit facility.  At December 31, 2012, KCP&L had $361.0 million of commercial paper outstanding at a weighted-average interest rate of 0.48%, had issued letters of credit totaling $13.9 million and had no outstanding cash borrowings under the credit facility.
	GMO's $450 Million Revolving Credit Facility and Commercial Paper
	In October 2013, GMO entered into an amendment to its $450 million revolving credit facility with a group of banks that provides support for its issuance of commercial paper and other general corporate purposes to extend the term to October 2018 from December 2016. As part of the amendment, Great Plains Energy no longer guarantees GMO's obligations under the credit facility.  Great Plains Energy and GMO may transfer up to $200 million of unused commitments between Great Plains Energy's and GMO's facilities.  A default by GMO or any of its significant subsidiaries on other indebtedness totaling more than $50.0 million is a default under the facility. Under the terms of this facility, GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times.  At September 30, 2013, GMO was in compliance with this covenant.  At September 30, 2013, GMO had $29.3 million of commercial paper outstanding at a weighted-average interest rate of 0.66%, had issued letters of credit totaling $14.6 million and had no outstanding cash borrowings under the credit facility.  At December 31, 2012, GMO had $169.1 million of commercial paper outstanding at a weighted-average interest rate of 0.94%, had issued letters of credit totaling $15.1 million and had no outstanding cash borrowings under the credit facility.

LongTerm_Debt

Long-Term Debt	9 Months Ended
	Sep. 30, 2013
Debt Disclosure [Abstract]	'
Long-Term Debt	'
	8. LONG-TERM DEBT
	Great Plains Energy's and KCP&L's long-term debt is detailed in the following table.
			September 30				December 31
		Year Due	2013				2012
	KCP&L			(millions)
	General Mortgage Bonds
	2.95% EIRR bonds(a)	2015-2035		$	146.4			$	106.9
	7.15% Series 2009A (8.59% rate)(b)	2019		400				400
	4.65% EIRR Series 2005	2035		50				50
	5.375% Series 2007B			—				73.2
	Senior Notes
	5.85% Series (5.72% rate)(b)	2017		250				250
	6.375% Series (7.49% rate)(b)	2018		350				350
	3.15% Series	2023		300				—
	6.05% Series (5.78% rate)(b)	2035		250				250
	5.30% Series	2041		400				400
	EIRR Bonds
	0.07% Series 2007A and 2007B(c)	2035		146.5				—
	2.875% Series 2008	2038		23.4				23.4
	Other			—				2.6
	Current maturities			—				(0.4		)
	Unamortized discount			(4.2		)		(4.0		)
	Total KCP&L excluding current maturities			2,312.10				1,901.70
	Other Great Plains Energy
	GMO First Mortgage Bonds 9.44% Series	2014-2021		9				10.1
	GMO Pollution Control Bonds
	0.158% Wamego Series 1996(c)	2026		7.3				7.3
	0.158% State Environmental 1993(c)	2028		5				5
	5.85% SJLP Pollution Control			—				5.6
	GMO Senior Notes
	8.27% Series	2021		80.9				80.9
	3.49% Series A	2025		125				—
	4.06% Series B	2033		75				—
	4.74% Series C	2043		150				—
	GMO Medium Term Notes
	7.16% Series	2013		6				6
	7.33% Series	2023		3				3
	7.17% Series	2023		7				7
	Great Plains Energy Senior Notes
	6.875% Series (7.33% rate)(b)	2017		100				100
	4.85% Series (7.34% rate)(b)	2021		350				350
	5.292% Series	2022		287.5				287.5
	2.75% Series (3.67% rate)(b)			—				250
	Current maturities			(7.1		)		(262.7		)
	Unamortized discount and premium, net			5.1				5.4
	Total Great Plains Energy excluding current maturities			$	3,515.80			$	2,756.80
	(a)	Weighted-average interest rates at September 30, 2013
	(b)	Rate after amortizing gains/losses recognized in OCI on settlements of interest rate hedging instruments
	(c)	Variable rate
	KCP&L Senior Notes
	In March 2013, KCP&L issued, at a discount, $300.0 million of 3.15% unsecured Senior Notes, maturing in 2023.
	EIRR Bond Remarketing
	In April 2013, KCP&L remarketed the following series of Environmental Improvement Revenue Refunding (EIRR) bonds:
	•	secured Series 1992 EIRR bonds maturing in 2017 totaling $31.0 million at a fixed rate of 1.25% through maturity;
	•	secured Series 1993B EIRR bonds totaling $39.5 million and previously held by KCP&L and 1993A EIRR bonds totaling $40.0 million maturing in 2023 at a fixed rate of 2.95% through maturity;
	•	unsecured Series 2007A-1 and 2007A-2 EIRR bonds totaling $10.0 million and $63.3 million, respectively, maturing in 2035 and previously held by KCP&L into one series: Series 2007A totaling $73.3 million at a variable rate that will be determined weekly; and
	•	unsecured Series 2007B EIRR bonds maturing in 2035 totaling $73.2 million at a variable rate that will be determined weekly.
	In connection with the remarketing of the bonds, the municipal bond insurance policies issued by Syncora
	Guarantee Inc. relating to the Series 1992 EIRR bonds and the Series 1993 EIRR bonds and by Financial Guaranty Insurance Company (FGIC) relating to the Series 2007 EIRR bond were cancelled. In connection with the cancellation of the policy relating to the Series 2007 EIRR bonds, KCP&L’s Mortgage Bond Series 2007 EIRR Insurer due 2035 was retired. This mortgage bond, in the amount of $146.5 million, was issued and delivered to FGIC in 2009 to collateralize FGIC’s claim on KCP&L under the related insurance agreement.
	In July 2013, KCP&L remarketed its unsecured Series 2008 EIRR bonds maturing in 2038 totaling $23.4 million at a fixed rate of 2.875% through July 1, 2018.
	GMO Senior Notes
	In August 2013, GMO entered into a note purchase agreement and issued the following series of unsecured senior notes:
	•	$125.0 million 3.49% Senior Notes, Series A, maturing in 2025;
•	$75.0 million 4.06% Senior Notes, Series B, maturing in 2033; and
•	$150.0 million 4.74% Senior Notes, Series C, maturing in 2043.
Under the terms of the note purchase agreement, GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the agreement, not greater than 0.65 to 1.00 at all times. In addition, GMO's priority debt, as defined in the agreement, cannot exceed 15% of consolidated tangible net worth, as defined in the agreement. At September 30, 2013, GMO was in compliance with these covenants.
Great Plains Energy Senior Notes
In August 2013, Great Plains Energy repaid its $250.0 million 2.75% Senior Notes at maturity.

Commitments_and_Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	9. COMMITMENTS AND CONTINGENCIES
	Environmental Matters
	Great Plains Energy and KCP&L are subject to extensive federal, state and local environmental laws, regulations and permit requirements relating to air and water quality, waste management and disposal, natural resources and health and safety.  In addition to imposing continuing compliance obligations and remediation costs, these laws, regulations and permits authorize the imposition of substantial penalties for noncompliance, including fines, injunctive relief and other sanctions.  The cost of complying with current and future environmental requirements is expected to be material to Great Plains Energy and KCP&L.  Failure to comply with environmental requirements or to timely recover environmental costs through rates could have a material effect on Great Plains Energy's and KCP&L's results of operations, financial position and cash flows.
	Great Plains Energy's and KCP&L's current estimate of capital expenditures (exclusive of Allowance for Funds Used During Construction (AFUDC) and property taxes) to comply with current final environmental regulations where the timing is certain is approximately $700 million.  The actual cost of compliance with any existing, proposed or future laws and regulations may be significantly different from the cost estimate provided.
	The current estimate of approximately $700 million of capital expenditures reflects costs to install environmental equipment at KCP&L's La Cygne Nos. 1 and 2 by June 2015 to comply with the Best Available Retrofit Technology (BART) rule and environmental upgrades at other coal-fired generating units through 2016 to comply with the Mercury and Air Toxics Standards (MATS) rule.
	In September 2011, KCP&L commenced construction of the La Cygne projects and at September 30, 2013, had incurred approximately $344 million of cash capital expenditures, which is included in the approximate $700 million estimate above.
	Great Plains Energy and KCP&L estimate that other capital projects at coal-fired generating units for compliance with the Clean Air Act and Clean Water Act based on proposed or final environmental regulations where the timing is uncertain could be approximately $600 million to $800 million for Great Plains Energy, which includes approximately $350 million to $450 million for KCP&L. However, these other projects are less certain and the timeframe cannot be estimated and therefore are not included in the approximately $700 million estimated cost of compliance discussed above.
	The Companies expect to seek recovery of the costs associated with environmental requirements through rate increases; however, there can be no assurance that such rate increases would be granted. The Companies may be subject to materially adverse rate treatment in response to competitive, economic, political, legislative or regulatory factors and/or public perception of the Companies' environmental reputation.
	The following discussion groups environmental and certain associated matters into the broad categories of air and climate change, water, solid waste and remediation.
	Clean Air Act and Climate Change Overview
	The Clean Air Act and associated regulations enacted by the Environmental Protection Agency (EPA) form a comprehensive program to preserve and enhance air quality.  States are required to establish regulations and programs to address all requirements of the Clean Air Act and have the flexibility to enact more stringent requirements.  All of Great Plains Energy's and KCP&L's generating facilities, and certain of their other facilities, are subject to the Clean Air Act.
	Clean Air Interstate Rule (CAIR) and Cross-State Air Pollution Rule (CSAPR)
	The CAIR requires reductions in SO2 and NOx emissions in 28 states, including Missouri, accomplished through statewide caps.  Great Plains Energy's and KCP&L's fossil fuel-fired plants located in Missouri are subject to CAIR, while their fossil fuel-fired plants in Kansas are not.
	In July 2008, the U.S. Court of Appeals for the D.C. Circuit (D.C. Circuit Court) vacated CAIR in its entirety and remanded the matter to the EPA to promulgate a new rule consistent with its opinion. In December 2008, the court issued an order reinstating CAIR pending EPA's development of a replacement regulation on remand. In July 2011, the EPA finalized the CSAPR to replace the currently-effective CAIR. The CSAPR required states within its scope to reduce power plant SO2 and NOx emissions that contribute to ozone and fine particle nonattainment in other states.  Compliance with the CSAPR was scheduled to begin in 2012.  Multiple states, utilities and other parties, including KCP&L, filed requests for reconsideration and stays with the EPA and/or the D.C. Circuit Court. In August 2012, the D.C. Circuit Court issued its opinion in which it vacated the CSAPR and remanded the rule to the EPA to revise in accordance with its opinion. The D.C. Circuit Court directed the EPA to continue to administer the CAIR until a valid replacement is promulgated.
	Best Available Retrofit Technology Rule
	The EPA BART rule directs state air quality agencies to identify whether visibility-reducing emissions from sources subject to BART are below limits set by the state or whether retrofit measures are needed to reduce emissions.  BART applies to specific eligible facilities including KCP&L's La Cygne Nos. 1 and 2 in Kansas; KCP&L's Iatan No. 1, in which GMO has an 18% interest, and KCP&L's Montrose No. 3 in Missouri; GMO's Sibley Unit No. 3 and Lake Road Unit No. 6 in Missouri; and Westar Energy, Inc.'s (Westar) Jeffrey Unit Nos. 1 and 2 in Kansas, in which GMO has an 8% interest.  Both Missouri and Kansas have approved BART plans.
	KCP&L has a consent agreement with the Kansas Department of Health and Environment (KDHE) incorporating limits for stack particulate matter emissions, as well as limits for NOx and SO2 emissions, at its La Cygne Station that will be below the presumptive limits under BART.  KCP&L further agreed to use its best efforts to install emission control technologies to reduce those emissions from the La Cygne Station prior to the required compliance date under BART, but in no event later than June 1, 2015.  In August 2011, KCC issued its order on KCP&L's predetermination request that would apply to the recovery of costs for its 50% share of the environmental equipment required to comply with BART at the La Cygne Station.  In the order, KCC stated that KCP&L's decision to retrofit La Cygne was reasonable, reliable, efficient and prudent and the $1.23 billion cost estimate is reasonable.  If the cost for the project is at or below the $1.23 billion estimate, absent a showing of fraud or other intentional imprudence, KCC stated that it will not re-evaluate the prudency of the cost of the project.  If the cost of the project exceeds the $1.23 billion estimate and KCP&L seeks to recover amounts exceeding the estimate, KCP&L will bear the burden of proving that any additional costs were prudently incurred.  KCP&L's 50% share of the estimated cost is $615 million.  KCP&L began the project in September 2011.
	Mercury and Air Toxics Standards Rule
	In December 2011, the EPA finalized the MATS rule that will reduce emissions of toxic air pollutants, also known as hazardous air pollutants, from new and existing coal- and oil-fired electric utility generating units with a capacity of greater than 25 MWs.  The rule establishes numerical emission limits for mercury, particulate matter (a surrogate for non-mercury metals) and hydrochloric acid (a surrogate for acid gases).  The rule establishes work practices, instead of numerical emission limits, for organic air toxics, including dioxin/furan. Compliance with the rule would need to be achieved by installing additional emission control equipment, changes in plant operation, purchasing additional power in the wholesale market or a combination of these and other alternatives.  The rule allows three to four years for compliance.
	Industrial Boiler Rule
	In December 2012, the EPA issued a final rule that would reduce emissions of hazardous air pollutants from new and existing industrial boilers.  The final rule establishes numeric emission limits for mercury, particulate matter (as a surrogate for non-mercury metals), hydrogen chloride (as a surrogate for acid gases) and carbon monoxide (as a surrogate for non-dioxin organic hazardous air pollutants).  The final rule establishes emission limits for KCP&L's and GMO's existing units that produce steam other than for the generation of electricity.  The final rule does not apply to KCP&L's and GMO's electricity generating boilers, but would apply to most of GMO's Lake Road boilers, which also serve steam customers, and to auxiliary boilers at other generating facilities. The rule allows three to four years for compliance.
	New Source Review
	The Clean Air Act's New Source Review program requires companies to obtain permits and, if necessary, install control equipment to reduce emissions when making a major modification or a change in operation if either is expected to cause a significant net increase in regulated emissions.
	In 2010, Westar settled a lawsuit filed by the Department of Justice on behalf of the EPA and agreed to install a selective catalytic reduction (SCR) system at one of the three Jeffrey Energy Center units by the end of 2014. The Jeffrey Energy Center is 92% owned by Westar and operated exclusively by Westar. GMO has an 8% interest in the Jeffrey Energy Center and is generally responsible for its 8% share of the facility's operating costs and capital expenditures. Westar has estimated the cost of this SCR at approximately $240 million.  Depending on the NOx emission reductions attained by that SCR and attainable through the installation of other controls at the other two units, the settlement agreement may require the installation of a second SCR system on one of the other two units. Westar has informed the EPA that they believe that the terms of the settlement can be met through the installation of less expensive NOx reduction equipment rather than a second SCR system and they plan to complete this project in 2014. GMO expects to seek recovery of its share of these costs through rate increases; however, there can be no assurance that such rate increases would be granted.
	SO2 NAAQS
	In June 2010, the EPA strengthened the primary National Ambient Air Quality Standard (NAAQS) for SO2 by establishing a new 1-hour standard at a level of 0.075 ppm and revoking the two existing primary standards of 0.140 ppm evaluated over 24 hours and 0.030 ppm evaluated over an entire year.  In July 2013, the EPA designated a part of Jackson County, Missouri, which is in the Companies' service territory, as a nonattainment area for the new 1-hour SO2 standard. The Missouri Department of Natural Resources (MDNR) will now develop and submit their plan to the EPA to return the area to attainment of the standard, which may include stricter controls on certain industrial facilities.
	Particulate Matter (PM) NAAQS
	In December 2012, the EPA strengthened the annual primary NAAQS for fine particulate matter (PM2.5). With the final rule, the EPA provided recent ambient air monitoring data for the Kansas City area indicating it would be in attainment of the revised fine particle standard. States will now make recommendations to designate areas as meeting the standards or not meeting them with the EPA making the final designation.
	Climate Change
	The Companies are subject to existing greenhouse gas reporting regulations and certain greenhouse gas permitting requirements.  Management believes it is possible that additional federal or relevant state or local laws or regulations could be enacted to address global climate change.  At the international level, while the United States is not a current party to the international Kyoto Protocol, it has agreed to undertake certain voluntary actions under the non-binding Copenhagen Accord and pursuant to subsequent international discussions relating to climate change, including the establishment of a goal to reduce greenhouse gas emissions.  International agreements legally binding on the United States may be reached in the future.  Such new laws or regulations could mandate new or increased requirements to control or reduce the emission of greenhouse gases, such as CO2, which are created in the combustion of fossil fuels.  The Companies' current generation capacity is primarily coal-fired and is estimated to produce about one ton of CO2 per MWh, or approximately 25 million tons and 19 million tons per year for Great Plains Energy and KCP&L, respectively.
	Legislation concerning the reduction of emissions of greenhouse gases, including CO2, is being considered at the federal and state levels.  The timing and effects of any such legislation cannot be determined at this time.  In the absence of new Congressional mandates, the EPA is proceeding with the regulation of greenhouse gases under the existing Clean Air Act.
	In June 2013, United States President Barack Obama announced a climate action plan and issued a presidential memorandum to address one element of the plan which is to reduce power plant carbon pollution. The memorandum directs the EPA to:
	(1) issue a new proposal addressing new units no later than September 20, 2013, and finalize the rule in a timely fashion;
	(2) issue proposed carbon pollution standards, regulations or guidelines, as appropriate, for modified, reconstructed and existing power plants by no later than June 1, 2014;
	(3) issue final standards, regulations or guidelines, as appropriate, for modified, reconstructed and existing power plants by no later than June 1, 2015;
	(4) include in the guidelines addressing existing power plants a requirement that states submit to the EPA the implementation plans by no later than June 30, 2016; and
	(5) engage with states, leaders in the power sector and other stakeholders on issues related to the rules.
	In September 2013, the EPA proposed new source performance standards for emissions of CO2 for new affected fossil-fuel-fired electric utility generating units.  This action pursuant to the Clean Air Act would, for the first time, set national limits on the amount of CO2 that power plants built in the future can emit.  The proposal would not apply to Great Plains Energy's and KCP&L's existing units including modifications to those units. The EPA withdrew its previous new unit proposal issued in March 2012.
	Greenhouse gas legislation or regulation has the potential of having significant financial and operational impacts on Great Plains Energy and KCP&L, including the potential costs and impacts of achieving compliance with limits that may be established.  However, the ultimate financial and operational consequences to Great Plains Energy and KCP&L cannot be determined until such legislation is passed and/or regulations are issued.  Management will continue to monitor the progress of relevant legislation and regulations.
	Laws have been passed in Missouri and Kansas, the states in which the Companies' retail electric businesses are operated, setting renewable energy standards, and management believes that national clean or renewable energy standards are also possible.  While management believes additional requirements addressing these matters will possibly be enacted, the timing, provisions and impact of such requirements, including the cost to obtain and install new equipment to achieve compliance, cannot be reasonably estimated at this time.
	A Kansas law enacted in May 2009 required Kansas public electric utilities, including KCP&L, to have renewable energy generation capacity equal to at least 10% of their three-year average Kansas peak retail demand by 2011 increasing to 15% by 2016 and 20% by 2020.  A Missouri law enacted in November 2008 required at least 2% of the electricity provided by Missouri investor-owned utilities (including KCP&L and GMO) to their Missouri retail customers to come from renewable resources, including wind, solar, biomass and hydropower, by 2011, increasing to 5% in 2014, 10% in 2018, and 15% in 2021, with a small portion (estimated to be about 2 MW for each of KCP&L and GMO) required to come from solar resources.
	KCP&L and GMO project that they will be compliant with the Missouri renewable requirements, exclusive of the solar requirement, through 2023 for KCP&L and 2018 for GMO.  KCP&L and GMO project that the acquisition of solar renewable energy credits will be sufficient for compliance with the Missouri solar requirements for the foreseeable future.  KCP&L also projects that it will be compliant with the Kansas renewable requirements through 2015.
	Clean Water Act
	The Clean Water Act and associated regulations enacted by the EPA form a comprehensive program to restore and preserve water quality.  Like the Clean Air Act, states are required to establish regulations and programs to address all requirements of the Clean Water Act, and have the flexibility to enact more stringent requirements.  All of Great Plains Energy's and KCP&L's generating facilities, and certain of their other facilities, are subject to the Clean Water Act.
	In March 2011, the EPA proposed regulations pursuant to Section 316(b) of the Clean Water Act regarding cooling water intake structures pursuant to a court approved settlement.  KCP&L generation facilities with cooling water intake structures would be subject to a limit on how many fish can be killed by being pinned against intake screens (impingement) and would be required to conduct studies to determine whether and what site-specific controls, if any, would be required to reduce the number of aquatic organisms drawn into cooling water systems (entrainment).  The EPA agreed to finalize the rule by November 2013.  Although the impact on Great Plains Energy's and KCP&L's operations will not be known until after the rule is finalized, it could have a significant effect on Great Plains Energy's and KCP&L's results of operations, financial position and cash flows.
	KCP&L holds a permit from the MDNR covering water discharge from its Hawthorn Station.  The permit authorizes KCP&L to, among other things, withdraw water from the Missouri River for cooling purposes and return the heated water to the Missouri River.  KCP&L has applied for a renewal of this permit and the EPA has submitted an interim objection letter regarding the allowable amount of heat that can be contained in the returned water.  Until this matter is resolved, KCP&L continues to operate under its current permit.  KCP&L cannot predict the outcome of this matter; however, while less significant outcomes are possible, this matter may require KCP&L to reduce its generation at Hawthorn Station, install cooling towers or both, any of which could have a significant impact on KCP&L's results of operations, financial position and cash flows.  The outcome could also affect the terms of water permit renewals at KCP&L's Iatan Station and at GMO's Sibley and Lake Road Stations.
	In April 2013, the EPA proposed to revise the technology-based effluent limitations guidelines and standards regulation to make the existing controls on discharges from steam electric power plants more stringent. The proposal sets the first federal limits on the levels of toxic metals in wastewater that can be discharged from power plants. The new requirements for existing power plants would be phased in between 2017 and 2022. The EPA is under a consent decree to take final action on the proposed rule by May 2014.
	The proposal includes a variety of options to reduce pollutants that are discharged into waterways by coal ash, air pollution control waste and other waste from steam electric power plants. Depending on the option, the proposed rule would establish new or additional requirements for wastewaters associated with the following processes and byproducts at certain KCP&L and GMO stations: flue gas desulfurization, fly ash, bottom ash, flue gas mercury control, combustion residual leachate from landfills and surface impoundments, and non-chemical metal cleaning wastes.
	The EPA also announced its intention to align this proposal with a related rule for coal combustion residuals (CCRs) proposed in May 2010 under the Resource Conservation and Recovery Act (RCRA). The EPA is considering establishing best management practices requirements that would apply to surface impoundments containing CCRs. The cost of complying with the proposed rules has the potential of having a significant financial and operational impact on Great Plains Energy and KCP&L.  However, the financial and operational consequences to Great Plains Energy and KCP&L cannot be determined until the final regulation is enacted.
	Solid Waste
	Solid and hazardous waste generation, storage, transportation, treatment and disposal is regulated at the federal and state levels under various laws and regulations.  In May 2010, the EPA proposed to regulate CCRs under the RCRA to address the risks from the disposal of CCRs generated from the combustion of coal at electric generating facilities.  The EPA is considering two options in this proposal.  Under the first option, the EPA would regulate CCRs as special wastes under subtitle C of RCRA (hazardous), when they are destined for disposal in landfills or surface impoundments.  Under the second option, the EPA would regulate disposal of CCRs under subtitle D of RCRA (non-hazardous).  The Companies use coal in generating electricity and dispose of the CCRs in both on-site facilities and facilities owned by third parties.  The cost of complying with the proposed CCR rule has the potential of having a significant financial and operational impact on Great Plains Energy and KCP&L.  However, the financial and operational consequences to Great Plains Energy and KCP&L cannot be determined until an option is selected by the EPA and the final regulation is enacted.
	Remediation
	Certain federal and state laws, including the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), hold current and previous owners or operators of contaminated facilities and persons who arranged for the disposal or treatment of hazardous substances liable for the cost of investigation and cleanup.  CERCLA and other laws also authorize the EPA and other agencies to issue orders compelling potentially responsible parties to clean up sites that are determined to present an actual or potential threat to human health or the environment.  GMO is named as a potentially responsible party at two disposal sites for polychlorinated biphenyl (PCB) contamination, and retains some environmental liability for several operations and investments it no longer owns.  In addition, GMO also owns, or has acquired liabilities from companies that once owned or operated, former manufactured gas plant (MGP) sites, which are subject to the supervision of the EPA and various state environmental agencies.
	At September 30, 2013, and December 31, 2012, KCP&L had $0.3 million accrued for environmental remediation expenses, which covers ground water monitoring at a former MGP site.  The amount accrued was established on an undiscounted basis and KCP&L does not currently have an estimated time frame over which the accrued amount may be paid.
	In addition to the $0.3 million accrual above, at September 30, 2013, and December 31, 2012, Great Plains Energy had $2.0 million accrued for the future investigation and remediation of certain additional GMO identified MGP sites and retained liabilities.  This estimate was based upon review of the potential costs associated with conducting investigative and remedial actions at identified sites, as well as the likelihood of whether such actions will be necessary.  This estimate could change materially after further investigation, and could also be affected by the actions of environmental agencies and the financial viability of other potentially responsible parties; however, given the uncertainty of these items the possible loss or range of loss in excess of the amount accrued is not estimable.
	GMO has pursued recovery of remediation costs from insurance carriers and other potentially responsible parties.  As a result of a settlement with an insurance carrier, approximately $2.6 million in insurance proceeds less an annual deductible is available to GMO to recover qualified MGP remediation expenses.  GMO would seek recovery of additional remediation costs and expenses through rate increases; however, there can be no assurance that such rate increases would be granted.

Legal_Proceedings

Legal Proceedings	9 Months Ended
	Sep. 30, 2013
Legal Proceedings [Abstract]	'
Legal Proceedings [Text Block]	'
	10. LEGAL PROCEEDINGS
	GMO Western Energy Crisis
	In response to complaints of manipulation of the California energy market, The Federal Energy Regulatory Commission (FERC) issued an order in July 2001 requiring net sellers of power in the California markets from October 2, 2000, through June 20, 2001, at prices above a FERC-determined competitive market clearing price, to make refunds to net purchasers of power in the California market during that time period.  Because MPS Merchant was a net purchaser of power during the refund period, it has received approximately $8 million in refunds through settlements with certain sellers of power.  MPS Merchant estimates that it is entitled to approximately $12 million in additional refunds under the standards FERC has used in this case.  FERC has stated that interest will be applied to the refunds but the amount of interest has not yet been determined.
	In December 2001, various parties appealed the July 2001 FERC order to the United States Court of Appeals for the Ninth Circuit (Ninth Circuit) seeking review of a number of issues, including expansion of the refund period to include periods prior to October 2, 2000 (the Summer Period).  MPS Merchant was a net seller of power during the Summer Period.  On August 2, 2006, the Ninth Circuit issued an order finding, among other things, that FERC did not provide a sufficient justification for refusing to exercise its remedial authority under the Federal Power Act to determine whether market participants violated FERC-approved tariffs during the Summer Period.  The court remanded the matter to FERC for further consideration.  If FERC determines that MPS Merchant violated then-existing tariffs or laws during the Summer Period and that such violations affected market clearing prices in California, MPS Merchant could be found to owe refunds. Due to the uncertainties remaining in this case, the potential refund or range of potential refunds owed by MPS Merchant are not reasonably estimable.

Related_Party_Transactions_and

Related Party Transactions and Relationships	9 Months Ended
	Sep. 30, 2013
Related Party Transactions [Abstract]	'
Related Party Transactions and Relationships	'
	11. RELATED PARTY TRANSACTIONS AND RELATIONSHIPS
	KCP&L employees manage GMO's business and operate its facilities at cost.  These costs totaled $32.7 million and $82.3 million, respectively, for the three months ended and year to date September 30, 2013. These costs totaled $23.9 million and $76.8 million, respectively, for the same periods in 2012.  Additionally, KCP&L and GMO engage in wholesale electricity transactions with each other.  KCP&L's net wholesale sales to GMO were $9.6 million and $19.6 million for the three months ended and year to date September 30, 2013, respectively. KCP&L's net wholesale sales to GMO were $6.3 million and $19.1 million, respectively, for the same periods in 2012.
	KCP&L and GMO are also authorized to participate in the Great Plains Energy money pool, an internal financing arrangement in which funds may be lent on a short-term basis to KCP&L and GMO from Great Plains Energy and between KCP&L and GMO. At December 31, 2012, KCP&L had a money pool payable to Great Plains Energy of $3.8 million.  The following table summarizes KCP&L's related party net receivables.
		September 30			December 31
			2013			2012
			(millions)
	Net receivable from GMO		$	23.6		$	26.2
	Net receivable from Great Plains Energy		16.8			13.8

Derivative_Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivative Instruments and Hedging Activities Disclosure [Text Block]	'
	12. DERIVATIVE INSTRUMENTS
	Great Plains Energy and KCP&L are exposed to a variety of market risks including interest rates and commodity prices.  Management has established risk management policies and strategies to reduce the potentially adverse effects that the volatility of the markets may have on Great Plains Energy's and KCP&L's operating results. Great Plains Energy's and KCP&L's interest rate risk management activities have included using derivative instruments to hedge against future interest rate fluctuations on anticipated debt issuances.  Commodity risk management activities, including the use of certain derivative instruments, are subject to the management, direction and control of an internal commodity risk committee.  Management maintains commodity price risk management strategies that use derivative instruments to reduce the effects of fluctuations in fuel and purchased power expense caused by commodity price volatility.
	Counterparties to commodity derivatives expose Great Plains Energy and KCP&L to credit loss in the event of nonperformance.  This credit loss is limited to the cost of replacing these contracts at current market rates. Derivative instruments, excluding those instruments that qualify for the normal purchases and normal sales (NPNS) election, which are accounted for by accrual accounting, are recorded on the balance sheet at fair value as an asset or liability.  Changes in the fair value of derivative instruments are recognized currently in net income unless specific hedge accounting criteria are met, except hedges for GMO's utility operations that are recorded to a regulatory asset or liability consistent with MPSC regulatory orders, as discussed below.
	Great Plains Energy and KCP&L have posted collateral, in the ordinary course of business, for the aggregate fair value of all derivative instruments with credit risk-related contingent features that are in a liability position.  At September 30, 2013, Great Plains Energy and KCP&L have posted collateral in excess of the aggregate fair value of their derivative instruments; therefore, if the credit risk-related contingent features underlying these agreements were triggered, Great Plains Energy and KCP&L would not be required to post additional collateral to their counterparties. For derivative contracts with counterparties under master netting agreements, Great Plains Energy and KCP&L can net all receivables and payables with each respective counterparty.
	Commodity Risk Management
	KCP&L's risk management policy is to use derivative instruments, as needed, in order to mitigate its exposure to market price fluctuations on a portion of its projected natural gas purchases to meet generation requirements for retail and firm wholesale sales. KCP&L designates these natural gas hedges as cash flow hedges. The fair values of these instruments are recorded as derivative assets or liabilities with an offsetting entry to OCI for the effective portion of the hedge. To the extent the hedges are not effective, any ineffective portion of the change in fair market value would be recorded currently in fuel expense.  At September 30, 2013, KCP&L had no hedges for its projected natural gas usage for retail load and firm MWh sales. KCP&L did not record any ineffectiveness on natural gas hedges for the three months ended and year to date September 30, 2013 and 2012.
	Additionally, KCP&L's risk management policy uses derivative instruments to mitigate exposure to market price fluctuations for wholesale power prices. KCP&L has designated these financial contracts as economic hedges (non-hedging derivatives). The fair values of these instruments are recorded as derivative assets or liabilities with an offsetting entry to the consolidated statements of income.
	GMO's risk management policy is to use derivative instruments to mitigate exposure to natural gas price volatility in the market.  At September 30, 2013, GMO had financial contracts in place to hedge approximately 28% and 5% of its expected on-peak natural gas generation and natural gas equivalent purchased power price exposure for 2014 and 2015, respectively. The fair value of the portfolio will settle against actual purchases of natural gas and purchased power.  GMO has designated its natural gas hedges as economic hedges (non-hedging derivatives).  In connection with GMO's 2005 Missouri electric rate case, it was agreed that the settlement costs of these contracts would be recognized in fuel expense. The settlement cost is included in GMO's Fuel Adjustment Clause (FAC).  A regulatory asset has been recorded to reflect the change in the timing of recognition authorized by the MPSC. Recovery of actual costs incurred will not impact earnings, but will impact cash flows due to the timing of the recovery mechanism.
	MPS Merchant, which has certain long-term natural gas contracts remaining from its former non-regulated trading operations, manages the daily delivery of its remaining contractual commitments with economic hedges (non-hedging derivatives) to reduce its exposure to changes in market prices.  Within the trading portfolio, MPS Merchant takes certain positions to hedge physical sale or purchase contracts.  MPS Merchant records the fair value of physical trading energy contracts as derivative assets or liabilities with an offsetting entry to the consolidated statements of income.
	The notional and recorded fair values of open positions for derivative instruments are summarized in the following table.  The fair values of these derivatives are recorded on the consolidated balance sheets.  The fair values below are gross values before netting agreements and netting of cash collateral.
		September 30								December 31
		2013								2012
		Notional				Fair				Notional			Fair
		Contract				Value				Contract			Value
		Amount								Amount
	Great Plains Energy	(millions)
	Futures contracts
	Cash flow hedges	$	—			$	—			$	1		$	(0.2	)
	Non-hedging derivatives	11				(1.2		)		17.9			(2.8		)
	Forward contracts
	Non-hedging derivatives	48.8				5.5				65.5			6.5
	Option contracts
	Non-hedging derivatives	3.2				0.5				—			—
	KCP&L
	Futures contracts
	Cash flow hedges	$	—			$	—			$	1		$	(0.2	)
	The fair values of Great Plains Energy's and KCP&L's open derivative positions are summarized in the following tables.  The tables contain both derivative instruments designated as hedging instruments as well as non-hedging derivatives under GAAP.  The fair values below are gross values before netting agreements and netting of cash collateral.
	Great Plains Energy
		Balance Sheet		Asset Derivatives						Liability Derivatives
	September 30, 2013	Classification		Fair Value						Fair Value
	Derivatives Not Designated as Hedging Instruments				(millions)
	Commodity contracts	Derivative instruments			$	6					$	1.2
	December 31, 2012
	Derivatives Designated as Hedging Instruments
	Commodity contracts	Derivative instruments			$	—					$	0.2
	Derivatives Not Designated as Hedging Instruments
	Commodity contracts	Derivative instruments			6.5						2.8
	Total Derivatives				$	6.5					$	3
	KCP&L
		Balance Sheet		Asset Derivatives						Liability Derivatives
	December 31, 2012	Classification		Fair Value						Fair Value
	Derivatives Designated as Hedging Instruments				(millions)
	Commodity contracts	Derivative instruments			$	—					$	0.2
	The following tables provide information regarding Great Plains Energy's and KCP&L's offsetting of derivative assets and liabilities.
	Great Plains Energy
																	Gross Amounts Not Offset in the Statement of Financial Position
	Description	Gross Amounts Recognized						Gross Amounts Offset in the Statement of Financial Position					Net Amounts Presented in the Statement of Financial Position				Financial Instruments				Cash Collateral Received			Net Amount
	30-Sep-13	(millions)
	Derivative assets		$	6					$	(0.1	)			$	5.9			$	—			$	—		$	5.9
	Derivative liabilities		1.2						(1.2		)			—				—				—			—
	31-Dec-12
	Derivative assets		$	6.5					$	—				$	6.5			$	—			$	—		$	6.5
	Derivative liabilities		3						(3.0		)			—				—				—			—
	KCP&L
																	Gross Amounts Not Offset in the Statement of Financial Position
	Description	Gross Amounts Recognized						Gross Amounts Offset in the Statement of Financial Position					Net Amounts Presented in the Statement of Financial Position				Financial Instruments				Cash Collateral Received			Net Amount
	31-Dec-12	(millions)
	Derivative liabilities		$	0.2					$	(0.2	)			$	—			$	—			$	—		$	—
	The following tables summarize the amount of gain (loss) recognized in OCI or earnings for interest rate and commodity hedges.
	Great Plains Energy
	Derivatives in Cash Flow Hedging Relationship
								Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)
		Amount of Gain  (Loss) Recognized in OCI on Derivatives  (Effective Portion)						Income Statement Classification		Amount
Three Months Ended September 30, 2013		(millions)							(millions)
Interest rate contracts		$	—				Interest charges		$	(4.6	)
Income tax benefit		—					Income tax benefit		1.8
Total		$	—				Total		$	(2.8	)
Year to Date September 30, 2013
Interest rate contracts		$	—				Interest charges		$	(14.3	)
Commodity contracts		—					Fuel		(0.2		)
Income tax benefit		—					Income tax benefit		5.6
Total		$	—				Total		$	(8.9	)
Three Months Ended September 30, 2012
Interest rate contracts		$	—				Interest charges		$	(5.0	)
Commodity contracts		0.1					Fuel		(0.5		)
Income tax expense		(0.1		)			Income tax benefit		2.1
Total		$	—				Total		$	(3.4	)
Year to Date September 30, 2012
Interest rate contracts		$	—				Interest charges		$	(15.1	)
Commodity contracts		(0.1		)			Fuel		(0.5		)
Income tax benefit		—					Income tax benefit		6
Total		$	(0.1	)			Total		$	(9.6	)
KCP&L
Derivatives in Cash Flow Hedging Relationship
							Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)
	Amount of Gain  (Loss) Recognized in OCI on Derivatives  (Effective Portion)						Income Statement Classification		Amount
Three Months Ended September 30, 2013		(millions)							(millions)
Interest rate contracts		$	—				Interest charges		$	(2.1	)
Income tax benefit		—					Income tax benefit		0.7
Total		$	—				Total		$	(1.4	)
Year to Date September 30, 2013
Interest rate contracts		$	—				Interest charges		$	(6.5	)
Commodity contracts		—					Fuel		(0.2		)
Income tax benefit		—					Income tax benefit		2.5
Total		$	—				Total		$	(4.2	)
Three Months Ended September 30, 2012
Interest rate contracts		$	—				Interest charges		$	(2.2	)
Commodity contracts		0.1					Fuel		(0.5		)
Income tax expense		(0.1		)			Income tax benefit		1
Total		$	—				Total		$	(1.7	)
Year to Date September 30, 2012
Interest rate contracts		$	—				Interest charges		$	(6.6	)
Commodity contracts		(0.1		)			Fuel		(0.5		)
Income tax benefit		—					Income tax benefit		2.7
Total		$	(0.1	)			Total		$	(4.4	)
The following table summarizes the amount of gain (loss) recognized in a regulatory asset or earnings for GMO utility commodity hedges.  GMO utility commodity derivatives fair value changes are recorded to either a regulatory asset or liability consistent with MPSC regulatory orders.
Great Plains Energy
Derivatives in Regulatory Account Relationship
							Gain (Loss) Reclassified from Regulatory Account
	Amount of Gain (Loss) Recognized in Regulatory Asset on Derivatives						Income Statement  Classification		Amount
Three Months Ended September 30, 2013	(millions)								(millions)
Commodity contracts		$	(0.1	)			Fuel		$	(0.3	)
Total		$	(0.1	)			Total		$	(0.3	)
Year to Date September 30, 2013
Commodity contracts		$	0.8				Fuel		$	(1.5	)
Total		$	0.8				Total		$	(1.5	)
Three Months Ended September 30, 2012
Commodity contracts		$	0.9				Fuel		$	(2.8	)
Total		$	0.9				Total		$	(2.8	)
Year to Date September 30, 2012
Commodity contracts		$	(1.8	)			Fuel		$	(5.5	)
Total		$	(1.8	)			Total		$	(5.5	)
Great Plains Energy's income statement reflects the gain (loss) for the change in fair value of commodity contract derivatives not designated as hedging instruments of an insignificant amount for the three months ended and year to date September 30, 2013, and $0.1 million and $(1.0) million, respectively, for the same periods in 2012. KCP&L's income statement reflects the gain for the change in fair value of commodity contract derivatives not designated as hedging instruments of $0.4 million and $1.0 million, respectively, for the three months ended and year to date September 30, 2013.
The amounts recorded in accumulated OCI related to the cash flow hedges are summarized in the following table.
	Great Plains Energy											KCP&L
	September 30						December 31					September 30				December 31
	2013						2012					2013				2012
		(millions)
Current assets		$	10					$	10.6				$	10			$	10.6
Current liabilities		(53.3		)				(68.4		)			(45.5		)		(52.8		)
Noncurrent liabilities		—						(0.1		)			—				(0.1		)
Deferred income taxes		16.8						22.5					13.9				16.5
Total		$	(26.5	)				$	(35.4	)			$	(21.6	)		$	(25.8	)
Great Plains Energy's accumulated OCI in the table above at September 30, 2013, includes $17.1 million that is expected to be reclassified to expenses over the next twelve months.  KCP&L's accumulated OCI in the table above at September 30, 2013, includes $8.7 million that is expected to be reclassified to expenses over the next twelve months.

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2013
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	13. FAIR VALUE MEASUREMENTS
	GAAP defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.  GAAP establishes a fair value hierarchy, which prioritizes the inputs to valuation techniques used to measure fair value into three broad categories, giving the highest priority to quoted prices in active markets for identical assets or liabilities and lowest priority to unobservable inputs.  A definition of the various levels, as well as discussion of the various measurements within the levels, is as follows:
	Level 1 – Unadjusted quoted prices for identical assets or liabilities in active markets that Great Plains Energy and KCP&L have access to at the measurement date.
	Level 2 – Market-based inputs for assets or liabilities that are observable (either directly or indirectly) or inputs that are not observable but are corroborated by market data.
	Level 3 – Unobservable inputs, reflecting Great Plains Energy's and KCP&L's own assumptions about the assumptions market participants would use in pricing the asset or liability.
	Great Plains Energy and KCP&L record cash and cash equivalents and short-term borrowings on the balance sheet at cost, which approximates fair value due to the short-term nature of these instruments.
	Great Plains Energy and KCP&L record long-term debt on the balance sheet at amortized cost. The fair value of long-term debt is measured as a Level 2 liability and is based on quoted market prices, with the incremental borrowing rate for similar debt used to determine fair value if quoted market prices are not available. At September 30, 2013, the book value and fair value of Great Plains Energy's long-term debt, including current maturities, were $3.5 billion and $3.7 billion, respectively. At December 31, 2012, the book value and fair value of Great Plains Energy's long-term debt, including current maturities, were $3.0 billion and $3.5 billion, respectively. At September 30, 2013, the book value and fair value of KCP&L's long-term debt, including current maturities, were $2.3 billion and $2.5 billion, respectively. At December 31, 2012, the book value and fair value of KCP&L's long-term debt, including current maturities, were $1.9 billion and $2.2 billion, respectively.
	The following tables include Great Plains Energy's and KCP&L's balances of financial assets and liabilities measured at fair value on a recurring basis.
												Fair Value Measurements Using
		September 30										Quoted Prices in Active Markets for Identical Assets			Significant Other Observable Inputs				Significant Unobservable Inputs
		2013										(Level 1)			(Level 2)				(Level 3)
	Description							Netting(d)
	KCP&L		(millions)
	Assets
	Nuclear decommissioning trust (a)
	Equity securities		$	117.5					$	—			$	117.5		$	—			$	—
	Debt securities
	U.S. Treasury		20.8						—				20.8			—				—
	U.S. Agency		2.4						—				—			2.4				—
	State and local obligations		3.2						—				—			3.2				—
	Corporate bonds		25.1						—				—			25.1				—
	Foreign governments		0.6						—				—			0.6				—
	Cash equivalents		5.3						—				—			5.3				—
	Other		(2.1		)				—				—			(2.1		)		—
	Total nuclear decommissioning trust		172.8						—				138.3			34.5				—
	Total		$	172.8					$	—			$	138.3		$	34.5			$	—
	Other Great Plains Energy
	Assets
	Derivative instruments (b)		$	5.9					$	(0.1	)		$	—		$	4.4			$	1.6
	SERP rabbi trusts (c)
	Equity securities		0.1						—				0.1			—				—
	Fixed income funds		18.7						—				—			18.7				—
	Total SERP rabbi trusts		18.8						—				0.1			18.7				—
	Total		24.7						(0.1		)		0.1			23.1				1.6
	Liabilities
	Derivative instruments (b)		—						(1.2		)		1.2			—				—
	Total		$	—					$	(1.2	)		$	1.2		$	—			$	—
	Great Plains Energy
	Assets
	Nuclear decommissioning trust (a)		$	172.8					$	—			$	138.3		$	34.5			$	—
	Derivative instruments (b)		5.9						(0.1		)		—			4.4				1.6
	SERP rabbi trusts (c)		18.8						—				0.1			18.7				—
	Total		197.5						(0.1		)		138.4			57.6				1.6
	Liabilities
	Derivative instruments (b)		—						(1.2		)		1.2			—				—
	Total		$	—					$	(1.2	)		$	1.2		$	—			$	—
												Fair Value Measurements Using
	Description	December 31						Netting(d)				Quoted Prices in Active Markets for Identical Assets			Significant Other Observable Inputs				Significant Unobservable Inputs
		2012										(Level 1)			(Level 2)				(Level 3)
	KCP&L		(millions)
	Assets
	Nuclear decommissioning trust (a)
	Equity securities		$	100.1					$	—			$	100.1		$	—			$	—
	Debt securities
	U.S. Treasury		18.5						—				18.5			—				—
	U.S. Agency		2.8						—				—			2.8				—
	State and local obligations		3.3						—				—			3.3				—
	Corporate bonds		26.8						—				—			26.8				—
	Other		0.3						—				—			0.3				—
	Total nuclear decommissioning trust		151.8						—				118.6			33.2				—
	Total		151.8						—				118.6			33.2				—
	Liabilities
	Derivative instruments (b)		—						(0.2		)		0.2			—				—
Total		$	—					$	(0.2	)		$	0.2		$	—			$	—
Other Great Plains Energy
Assets
Derivative instruments (b)		$	6.5					$	—			$	—		$	4.2			$	2.3
SERP rabbi trusts (c)
Equity securities		0.1						—				0.1			—				—
Fixed income funds		20.2						—				—			20.2				—
Total SERP rabbi trusts		20.3						—				0.1			20.2				—
Total		26.8						—				0.1			24.4				2.3
Liabilities
Derivative instruments (b)		—						(2.8		)		2.8			—				—
Total		$	—					$	(2.8	)		$	2.8		$	—			$	—
Great Plains Energy
Assets
Nuclear decommissioning trust (a)		$	151.8					$	—			$	118.6		$	33.2			$	—
Derivative instruments (b)		6.5						—				—			4.2				2.3
SERP rabbi trusts (c)		20.3						—				0.1			20.2				—
Total		178.6						—				118.7			57.6				2.3
Liabilities
Derivative instruments (b)		—						(3.0		)		3			—				—
Total		$	—					$	(3.0	)		$	3		$	—			$	—
(a)	Fair value is based on quoted market prices of the investments held by the fund and/or valuation models.  The total does not include $2.9 million of cash and cash equivalents at December 31, 2012.
(b)	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.
(c)	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.
(d)	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 September 30, 2013, and December 31, 2012, Great Plains Energy netted $1.1 million and $3.0 million, respectively, of cash collateral posted with counterparties.
The following tables reconcile the beginning and ending balances for all Level 3 assets measured at fair value on a recurring basis.
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Derivative Instruments
	2013				2012
	(millions)
Balance at July 1	$	1.9			$	2.2
Total realized/unrealized gains included in non-operating income	1				3.7
Settlements	(1.3		)		(3.5		)
Balance at September 30	$	1.6			$	2.4
Total unrealized gains (losses) included in non-operating income relating to assets
still on the consolidated balance sheet at September 30	$	(0.3	)		$	0.3
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Derivative Instruments
	2013				2012
	(millions)
Balance at January 1	$	2.3			$	3.1
Total realized/unrealized gains included in non-operating income	5.3				4.8
Settlements	(6.0		)		(5.5		)
Balance at September 30	$	1.6			$	2.4
Total unrealized losses included in non-operating income relating to assets
still on the consolidated balance sheet at September 30	$	(0.4	)		$	(0.4	)

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income (Loss) (Notes)	9 Months Ended
	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Abstract]	'
Accumulated Other Comprehensive Income (Loss) [Text Block]	'
	14. ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)
	The following tables reflect the change in the balances of each component of accumulated other comprehensive loss for Great Plains Energy and KCP&L.
	Great Plains Energy
		Gains and Losses on Cash Flow Hedges(a)				Defined Benefit Pension Items(a)				Total(a)
		(millions)
	Beginning balance January 1, 2013		$	(35.4	)		$	(3.0	)	$	(38.4	)
	Amounts reclassified from accumulated other comprehensive loss		8.9				0.3			9.2
	Net current period other comprehensive income		8.9				0.3			9.2
	Ending balance September 30, 2013		$	(26.5	)		$	(2.7	)	$	(29.2	)
	(a) Net of tax
	KCP&L
		Gains and Losses on Cash Flow Hedges(a)
		(millions)
	Beginning balance January 1, 2013		$	(25.8	)
	Amounts reclassified from accumulated other comprehensive loss		4.2
	Net current period other comprehensive income		4.2
	Ending balance September 30, 2013		$	(21.6	)
	(a) Net of tax
	The following tables reflect the effect on certain line items of net income from amounts reclassified out of each component of accumulated other comprehensive loss for Great Plains Energy and KCP&L.
	Great Plains Energy
	Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Loss				Affected Line Item in the Income Statement
	Three Months Ended September 30, 2013	(millions)
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts		$	(4.6	)	Interest charges
			(4.6		)	Income before income tax expense and loss from equity investments
			1.8			Income tax benefit
			$	(2.8	)	Net income
	Amortization of defined benefit pension items
	Net losses included in net periodic benefit costs		$	(0.1	)	Utility operating and maintenance expenses
			(0.1		)	Income before income tax expense and loss from equity investments
			—			Income tax benefit
			(0.1		)	Net income
	Total reclassifications, net of tax		$	(2.9	)	Net income
	Year to Date September 30, 2013
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts		$	(14.3	)	Interest charges
	Commodity contracts		(0.2		)	Fuel
			(14.5		)	Income before income tax expense and loss from equity investments
			5.6			Income tax benefit
			$	(8.9	)	Net income
	Amortization of defined benefit pension items
	Net losses included in net periodic benefit costs		$	(0.4	)	Utility operating and maintenance expenses
			(0.4		)	Income before income tax expense and loss from equity investments
			0.1			Income tax benefit
			(0.3		)	Net income
	Total reclassifications, net of tax		$	(9.2	)	Net income
	KCP&L
	Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Loss				Affected Line Item in the Income Statement
	Three Months Ended September 30, 2013	(millions)
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts		$	(2.1	)	Interest charges
			(2.1		)	Income before income tax expense
			0.7			Income tax benefit
	Total reclassifications, net of tax		$	(1.4	)	Net income
	Year to Date September 30, 2013
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts		$	(6.5	)	Interest charges
	Commodity contracts		(0.2		)	Fuel
			(6.7		)	Income before income tax expense
			2.5			Income tax benefit
	Total reclassifications, net of tax		$	(4.2	)	Net income

Taxes

Taxes	9 Months Ended
	Sep. 30, 2013
Income Tax Disclosure [Abstract]	'
Income Tax Disclosure [Text Block]	'
	15. TAXES
	Components of income tax expense are detailed in the following tables.
		Three Months Ended								Year to Date
		30-Sep								30-Sep
	Great Plains Energy	2013				2012				2013			2012
	Current income taxes	(millions)
	Federal	$	1			$	(1.4	)		$	1		$	(4.7	)
	State	(0.4		)		(0.3		)		(0.3		)	—
	Total	0.6				(1.7		)		0.7			(4.7		)
	Deferred income taxes
	Federal	67.9				75.1				105.4			97.6
	State	13.3				13.9				21.3			18.2
	Total	81.2				89				126.7			115.8
	Noncurrent income taxes
	Federal	—				—				—			(0.2		)
	State	—				—				(0.2		)	—
	Foreign	0.1				(4.1		)		(0.2		)	(4.2		)
	Total	0.1				(4.1		)		(0.4		)	(4.4		)
	Investment tax credit
	Deferral	0.3				—				0.3			—
	Amortization	(0.4		)		(0.6		)		(1.3		)	(1.8		)
	Total	(0.1		)		(0.6		)		(1.0		)	(1.8		)
	Income tax expense	$	81.8			$	82.6			$	126		$	104.9
		Three Months Ended								Year to Date
		30-Sep								30-Sep
	KCP&L	2013				2012				2013			2012
	Current income taxes	(millions)
	Federal	$	(0.6	)		$	22.9			$	(1.2	)	$	23.1
	State	(0.4		)		4.1				(0.5		)	4.2
	Total	(1.0		)		27				(1.7		)	27.3
	Deferred income taxes
	Federal	55				22.7				75.6			38.8
	State	10.9				4.5				15.9			8.6
	Total	65.9				27.2				91.5			47.4
	Noncurrent income taxes
	Federal	(10.1		)		1				(9.0		)	1.1
	State	(1.7		)		0.2				(1.5		)	0.2
	Total	(11.8		)		1.2				(10.5		)	1.3
	Investment tax credit
	Deferral	0.3				—				0.3			—
	Amortization	(0.3		)		(0.5		)		(0.8		)	(1.4		)
	Total	—				(0.5		)		(0.5		)	(1.4		)
	Income tax expense	$	53.1			$	54.9			$	78.8		$	74.6
	Effective Income Tax Rates
	Effective income tax rates reflected in the financial statements and the reasons for their differences from the statutory federal rates are detailed in the following tables.
		Three Months Ended						Year to Date
		30-Sep						30-Sep
	Great Plains Energy	2013			2012			2013			2012
	Federal statutory income tax rate	35	%		35	%		35	%		35	%
	Differences between book and tax depreciation not normalized	(0.5	)		0.5			(0.2	)		1.1
	Amortization of investment tax credits	(0.2	)		(0.3	)		(0.4	)		(0.6	)
	Federal income tax credits	(1.6	)		(1.0	)		(2.8	)		(2.8	)
	State income taxes	3.7			3.8			3.8			3.9
	Changes in uncertain tax positions, net	0.1			(1.8	)		(0.1	)		(1.4	)
	Other	(0.1	)		(0.1	)		(0.2	)		(0.3	)
	Effective income tax rate	36.4	%		36.1	%		35.1	%		34.9	%
		Three Months Ended						Year to Date
		30-Sep						30-Sep
	KCP&L	2013			2012			2013			2012
	Federal statutory income tax rate	35	%		35	%		35	%		35	%
	Differences between book and tax depreciation not normalized	(0.9	)		0.7			(0.6	)		1.3
	Amortization of investment tax credits	(0.2	)		(0.3	)		(0.3	)		(0.6	)
	Federal income tax credits	(2.2	)		(1.5	)		(4.2	)		(4.0	)
State income taxes	3.8			3.9			3.8			4
Changes in uncertain tax positions, net	0.1			—			—			—
Other	(0.1	)		—			(0.2	)		(0.3	)
Effective income tax rate	35.5	%		37.8	%		33.5	%		35.4	%
Uncertain Tax Positions
At September 30, 2013, and December 31, 2012, Great Plains Energy had $10.2 million and $21.4 million, respectively, of liabilities related to unrecognized tax benefits.  Of these amounts, $6.8 million and $7.3 million at September 30, 2013, and December 31, 2012, respectively, were expected to impact the effective tax rate if recognized.  The $11.2 million decrease in unrecognized tax benefits is primarily due to a change in certain income tax accounting methods for the capitalization of assets at KCP&L. This reduction in unrecognized tax benefits is offset by an increase to deferred income tax liabilities since the unrecognized tax benefits were related to temporary tax differences.
At September 30, 2013, and December 31, 2012, KCP&L had none and $10.5 million, respectively, of liabilities related to unrecognized tax benefits. None of these amounts were expected to impact the effective tax rate if recognized.  The $10.5 million decrease in unrecognized tax benefits is primarily due to a change in certain income tax accounting methods for the capitalization of assets at KCP&L. This reduction in unrecognized tax benefits is offset by an increase to deferred income tax liabilities since the unrecognized tax benefits were related to temporary tax differences.
The following table reflects activity for Great Plains Energy and KCP&L related to the liability for unrecognized tax benefits.
		Great Plains Energy											KCP&L
	September 30						December 31					September 30				December 31
	2013						2012					2013				2012
		(millions)
Beginning balance January 1		$	21.4					$	24				$	10.5			$	8.7
Additions for current year tax positions		—						3.7					—				3.6
Reductions for current year tax positions		(0.3		)				—					—				—
Reductions for prior year tax positions		(10.5		)				(1.8		)			(10.5		)		(1.6		)
Statute expirations		(0.2		)				(4.7		)			—				(0.2		)
Foreign currency translation adjustments		(0.2		)				0.2					—				—
Ending balance		$	10.2					$	21.4				$	—			$	10.5
Great Plains Energy and KCP&L recognize interest related to unrecognized tax benefits in interest expense and penalties in non-operating expenses.  At September 30, 2013, and December 31, 2012, amounts accrued for interest related to unrecognized tax benefits for Great Plains Energy were $3.3 million and $3.5 million, respectively. Amounts accrued for penalties with respect to unrecognized tax benefits for Great Plains Energy were $0.6 million and $0.7 million at September 30, 2013, and December 31, 2012, respectively. At September 30, 2013, and December 31, 2012, amounts accrued for interest and penalties with respect to unrecognized tax benefits for KCP&L were insignificant.
The Internal Revenue Service (IRS) is currently auditing Great Plains Energy and its subsidiaries for the 2009 tax year. The Company estimates that it is reasonably possible that $7.2 million of other unrecognized tax benefits for Great Plains Energy may be recognized in the next twelve months due to statute expirations or settlement agreements with tax authorities.
Tangible Property Regulations
In September 2013, the IRS released final regulations regarding amounts paid to acquire, produce or improve tangible property. In addition, proposed regulations were issued regarding the treatment of retirements of depreciable property and general asset accounts. The final regulations are effective for tax years beginning on or after January 1, 2014, for all taxpayers that acquire, produce or improve tangible property. The new regulations are not expected to have a significant impact on Great Plains Energy’s and KCP&L’s results of operations, financial position and cash flows.

Segments_and_Related_Informati

Segments and Related Information	9 Months Ended
	Sep. 30, 2013
Segment Reporting [Abstract]	'
Segments and Related Information	'
	16. SEGMENTS AND RELATED INFORMATION
	Great Plains Energy has one reportable segment based on its method of internal reporting, which segregates reportable segments based on products and services, management responsibility and regulation.  The one reportable business segment is electric utility, consisting of KCP&L, GMO's regulated utility operations and GMO Receivables Company.  Other includes GMO activity other than its regulated utility operations and unallocated corporate charges.  The summary of significant accounting policies applies to the reportable segment.  Segment performance is evaluated based on net income attributable to Great Plains Energy.
	The following tables reflect summarized financial information concerning Great Plains Energy's reportable segment.
	Three Months Ended	Electric				Other				Eliminations				Great Plains
	30-Sep-13	Utility												Energy
		(millions)
	Operating revenues		$	765			$	—			$	—			$	765
	Depreciation and amortization		(73.3		)		—				—				(73.3		)
	Interest charges		(46.7		)		(13.6		)		11.4				(48.9		)
	Income tax (expense) benefit		(83.6		)		1.8				—				(81.8		)
	Net income (loss) attributable to Great Plains Energy		145.4				(2.3		)		—				143.1
	Year to Date	Electric				Other				Eliminations				Great Plains
	30-Sep-13	Utility												Energy
		(millions)
	Operating revenues		$	1,907.50			$	—			$	—			$	1,907.50
	Depreciation and amortization		(216.1		)		—				—				(216.1		)
	Interest charges		(141.9		)		(42.7		)		36.6				(148.0		)
	Income tax (expense) benefit		(130.1		)		4.1				—				(126.0		)
	Net income (loss) attributable to Great Plains Energy		238.5				(5.8		)		—				232.7
	Three Months Ended	Electric				Other				Eliminations				Great Plains
	30-Sep-12	Utility												Energy
		(millions)
	Operating revenues		$	746.2			$	—			$	—			$	746.2
	Depreciation and amortization		(68.9		)		—				—				(68.9		)
	Interest charges		(48.4		)		(12.3		)		12.6				(48.1		)
	Income tax (expense) benefit		(86.5		)		3.9				—				(82.6		)
	Net income attributable to Great Plains Energy		141.9				4.3				—				146.2
	Year to Date	Electric				Other				Eliminations				Great Plains
	30-Sep-12	Utility												Energy
		(millions)
	Operating revenues		$	1,829.50			$	—			$	—			$	1,829.50
	Depreciation and amortization		(204.2		)		—				—				(204.2		)
	Interest charges		(149.5		)		(52.5		)		31.2				(170.8		)
	Income tax (expense) benefit		(120.6		)		15.7				—				(104.9		)
	Net income (loss) attributable to Great Plains Energy		210.2				(15.0		)		—				195.2
		Electric				Other				Eliminations				Great Plains
		Utility												Energy
	September 30, 2013		(millions)
	Assets		$	10,193.90			$	87.8			$	(412.5	)		$	9,869.20
	Capital expenditures(a)		486.2				—				—				486.2
	December 31, 2012
	Assets		$	9,910.60			$	122.4			$	(385.7	)		$	9,647.30
	Capital expenditures(a)		610.2				—				—				610.2
	(a) Capital expenditures reflect year to date amounts for the periods presented.

Regulatory_Matters

Regulatory Matters	9 Months Ended
	Sep. 30, 2013
Regulated Operations [Abstract]	'
Regulatory Matters	'
	17. REGULATORY MATTERS
	KCP&L Missouri Rate Case Proceedings
	On January 9, 2013, the MPSC issued an order for KCP&L authorizing an increase in annual revenues of $67.4 million effective January 26, 2013. Appeals of the January 9, 2013, MPSC order were filed in February 2013 with the Missouri Court of Appeals, Western District (Court of Appeals) by KCP&L and the Missouri Energy Consumers Group (MECG) regarding various issues. On May 16, 2013, the Court of Appeals granted KCP&L's request to withdraw its appeal.
	On January 23, 2013, the MPSC issued an order granting expedited treatment and approving compliance tariffs implementing rates reflecting the increase in annual revenues authorized in the January 9, 2013, order. On February 6, 2013, the Office of Public Counsel (OPC) filed a Writ of Mandamus asking the Court of Appeals to direct the MPSC to vacate and rescind its January 23, 2013, order approving the tariffs because the order did not provide the OPC with a reasonable amount of time to review and/or file a motion for rehearing on the tariffs. On September 10, 2013, the Court of Appeals granted the Writ of Mandamus. On October 9, 2013, the MPSC issued an order vacating its January 23, 2013, order approving the expedited tariffs, effective November 8, 2013.
	The MECG also appealed the January 23, 2013, order in February 2013. The Court of Appeals has not yet issued its decision on the MECG appeal.
	The rates established by the January 9, 2013, MPSC order are effective unless and until modified by the MPSC or stayed by a court.
	GMO Missouri Rate Case Proceedings
	On January 9, 2013, the MPSC issued an order for GMO authorizing an increase in annual revenues of $26.2 million for its Missouri Public Service division and $21.7 million for its St. Joseph Light & Power (L&P) division effective January 26, 2013. Appeals of the January 9, 2013, MPSC order were filed in February 2013 with the Court of Appeals by GMO and MECG regarding various issues.
	On January 23, 2013, the MPSC issued an order granting expedited treatment and approving compliance tariffs implementing rates reflecting the increase in annual revenues authorized in the January 9, 2013, order. On February 6, 2013, the OPC filed a Writ of Mandamus asking the Court of Appeals to direct the MPSC to vacate and rescind its January 23, 2013, order approving the tariffs because the order did not provide the OPC with a reasonable amount of time to review and/or file a motion for rehearing on the tariffs. On September 10, 2013, the Court of Appeals granted the Writ of Mandamus. On October 9, 2013, the MPSC issued an order vacating its January 23, 2013, order approving the expedited tariffs, effective November 8, 2013.
	The MECG also appealed the January 23, 2013, order in February 2013. The Court of Appeals has not yet issued its decision on the appeals.
	The rates established by the January 9, 2013, MPSC order are effective unless and until modified by the MPSC or stayed by a court.

Goodwill_and_Intangible_Assets

Goodwill and Intangible Assets	9 Months Ended
	Sep. 30, 2013
Goodwill and Intangible Assets Disclosure [Abstract]	'
Goodwill and Intangible Assets [Text Block]	'
	18. GOODWILL
	Accounting rules require goodwill to be tested for impairment annually and when an event occurs indicating the possibility that an impairment exists. The annual impairment test for the $169.0 million of GMO acquisition goodwill was conducted on September 1, 2013. The goodwill impairment test is a two step process. The first step compares the fair value of a reporting unit to its carrying amount, including goodwill, to identify potential impairment. If the carrying amount exceeds the fair value of the reporting unit, the second step of the test is performed, consisting of assignment of the reporting unit's fair value to its assets and liabilities to determine an implied fair value of goodwill, which is compared to the carrying amount of goodwill to determine the impairment loss, if any, to be recognized in the financial statements. Great Plains Energy's regulated electric utility operations are considered one reporting unit for assessment of impairment, as they are included within the same operating segment and have similar economic characteristics. The determination of fair value of the reporting unit consisted of two valuation techniques: an income approach consisting of a discounted cash flow analysis and a market approach consisting of a determination of reporting unit invested capital using market multiples derived from the historical revenue, EBITDA and net utility asset values and market prices of stock of electric and gas company regulated peers. The results of the two techniques were evaluated and weighted to determine a point within the range that management considered representative of fair value for the reporting unit. Fair value of the reporting unit exceeded the carrying amount, including goodwill; therefore, there was no impairment of goodwill.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Organization [Policy Text Block]	'
	Organization
	Great Plains Energy, a Missouri corporation incorporated in 2001, is a public utility holding company and does not own or operate any significant assets other than the stock of its subsidiaries.  Great Plains Energy's wholly owned direct subsidiaries with operations or active subsidiaries are as follows:
	•	KCP&L is an integrated, regulated electric utility that provides electricity to customers primarily in the states of Missouri and Kansas.  KCP&L has one active wholly owned subsidiary, Kansas City Power & Light Receivables Company (KCP&L Receivables Company).
	•	KCP&L Greater Missouri Operations Company (GMO) is an integrated, regulated electric utility that primarily provides electricity to customers in the state of Missouri.  GMO also provides regulated steam service to certain customers in the St. Joseph, Missouri area.  GMO has two active wholly owned subsidiaries, GMO Receivables Company and MPS Merchant Services, Inc. (MPS Merchant).  MPS Merchant has certain long-term natural gas contracts remaining from its former non-regulated trading operations.
	Each of Great Plains Energy's and KCP&L's consolidated financial statements includes the accounts of their subsidiaries.  Intercompany transactions have been eliminated.
	Great Plains Energy's sole reportable business segment is electric utility.  See Note 16 for additional information.
Basic and Diluted Earnings per Common Share Calculation [Policy Text Block]	'
	Basic and Diluted Earnings per Common Share Calculation
	To determine basic EPS, preferred stock dividend requirements and net income attributable to noncontrolling interest are deducted from net income before dividing by the average number of common shares outstanding.  The effect of dilutive securities, calculated using the treasury stock method, assumes the issuance of common shares applicable to performance shares, restricted stock and Equity Units. Great Plains Energy settled the Equity Units in June 2012.
	The following table reconciles Great Plains Energy's basic and diluted EPS.
			Three Months Ended						Year to Date
			30-Sep						30-Sep
			2013			2012			2013		2012
	Income		(millions, except per share amounts)
	Net income		$	143.1		$	146.4		$	232.7	$	195.2
	Less: net income attributable to noncontrolling interest		—			0.2			—		—
	Less: preferred stock dividend requirements		0.4			0.4			1.2		1.2
	Earnings available for common shareholders		$	142.7		$	145.8		$	231.5	$	194
	Common Shares Outstanding
	Average number of common shares outstanding		153.6			153.2			153.5		142.9
	Add: effect of dilutive securities		0.2			0.2			0.2		2.1
	Diluted average number of common shares outstanding		153.8			153.4			153.7		145
	Basic EPS		$	0.93		$	0.95		$	1.51	$	1.36
	Diluted EPS		$	0.93		$	0.95		$	1.51	$	1.34
	Anti-dilutive shares excluded from the computation of diluted EPS are detailed in the following table.
			Three Months Ended					Year to Date
			30-Sep					30-Sep
			2013		2012			2013		2012
	Performance shares		54,660		192,723			54,660		209,000
	Restricted stock shares		—		2,531			21,652		2,531

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	'
	The following table reconciles Great Plains Energy's basic and diluted EPS.
		Three Months Ended						Year to Date
		30-Sep						30-Sep
		2013			2012			2013		2012
	Income	(millions, except per share amounts)
	Net income	$	143.1		$	146.4		$	232.7	$	195.2
	Less: net income attributable to noncontrolling interest	—			0.2			—		—
	Less: preferred stock dividend requirements	0.4			0.4			1.2		1.2
	Earnings available for common shareholders	$	142.7		$	145.8		$	231.5	$	194
	Common Shares Outstanding
	Average number of common shares outstanding	153.6			153.2			153.5		142.9
	Add: effect of dilutive securities	0.2			0.2			0.2		2.1
	Diluted average number of common shares outstanding	153.8			153.4			153.7		145
	Basic EPS	$	0.93		$	0.95		$	1.51	$	1.36
	Diluted EPS	$	0.93		$	0.95		$	1.51	$	1.34
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]	'
	Anti-dilutive shares excluded from the computation of diluted EPS are detailed in the following table.
		Three Months Ended					Year to Date
		30-Sep					30-Sep
		2013		2012			2013		2012
	Performance shares	54,660		192,723			54,660		209,000
	Restricted stock shares	—		2,531			21,652		2,531

Supplemental_Cash_Flow_Informa1

Supplemental Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2013
Supplemental Cash Flow Elements [Abstract]	'
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	'
	Great Plains Energy Other Operating Activities
	Year to Date September 30	2013			2012
	Cash flows affected by changes in:	(millions)
	Receivables	$	(44.1	)	$	12.5
	Accounts receivable pledged as collateral	(16.0		)	(95.0		)
	Fuel inventories	11.2			(5.4		)
	Materials and supplies	(4.3		)	(7.8		)
	Accounts payable	(91.5		)	(49.4		)
	Accrued taxes	81			65.4
	Accrued interest	18.4			(16.6		)
	Deferred refueling outage costs	(21.8		)	13.4
	Pension and post-retirement benefit obligations	40.2			21.9
	Allowance for equity funds used during construction	(9.1		)	(0.3		)
	Fuel recovery mechanism	(5.3		)	13.1
	Uncertain tax positions	(0.4		)	(4.4		)
	Other	(8.4		)	(14.2		)
	Total other operating activities	$	(50.1	)	$	(66.8	)
	Cash paid during the period:
	Interest	$	111.3		$	185.4
	Income taxes	$	0.1		$	3.3
	Non-cash investing activities:
	Liabilities accrued for capital expenditures	$	34.5		$	52.2
	KCP&L Other Operating Activities
	Year to Date September 30	2013			2012
	Cash flows affected by changes in:	(millions)
	Receivables	$	(40.2	)	$	(35.1	)
	Accounts receivable pledged as collateral	—			(15.0		)
	Fuel inventories	10.4			(6.2		)
	Materials and supplies	(3.0		)	(6.1		)
	Accounts payable	(66.7		)	(18.0		)
	Accrued taxes	55.3			76.5
	Accrued interest	12.2			9.8
	Deferred refueling outage costs	(21.8		)	13.4
	Pension and post-retirement benefit obligations	41.9			24.7
	Allowance for equity funds used during construction	(9.1		)	(0.3		)
	Fuel recovery mechanism	(1.2		)	(0.9		)
	Uncertain tax positions	(10.5		)	1.2
	Other	(6.1		)	(20.6		)
	Total other operating activities	$	(38.8	)	$	23.4
	Cash paid during the period:
	Interest	$	73.2		$	77.3
	Income taxes	$	—		$	—
	Non-cash investing activities:
	Liabilities accrued for capital expenditures	$	28.3		$	48

Receivables_Tables

Receivables (Tables)	9 Months Ended
	Sep. 30, 2013
Receivables [Abstract]	'
Schedule of receivables [Table Text Block]	'
	Great Plains Energy's and KCP&L's receivables are detailed in the following table.
		September 30				December 31
			2013				2012
	Great Plains Energy		(millions)
	Customer accounts receivable - billed		$	24.4			$	—
	Customer accounts receivable - unbilled		89.7				58.3
	Allowance for doubtful accounts - customer accounts receivable		(3.4		)		(2.6		)
	Other receivables		88.4				98.8
	Total		$	199.1			$	154.5
	KCP&L
	Customer accounts receivable - billed		$	23.8			$	—
	Customer accounts receivable - unbilled		64.7				42.9
	Allowance for doubtful accounts - customer accounts receivable		(1.9		)		(1.5		)
	Intercompany receivables		40.4				40
	Other receivables		80.3				81.8
	Total		$	207.3			$	163.2
Schedule of accounts receivable sold [Table Text Block]	'
	Information regarding KCP&L's sale of accounts receivable to KCP&L Receivables Company and GMO's sale of accounts receivable to GMO Receivables Company is reflected in the following tables.
	Three Months Ended	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
	30-Sep-13					Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(481.2	)		$	481.2			$	—			$	(264.1	)		$	264.1			$	—
	Gain (loss) on sale of accounts receivable (a)		(6.1		)		5.8				(0.3		)		(3.4		)		3.2				(0.5		)
	Servicing fees received (paid)		0.8				(0.8		)		—				0.4				(0.4		)		—
	Fees paid to outside investor		—				(0.3		)		(0.3		)		—				(0.2		)		(0.5		)
	Cash from customers (transferred) received		(468.5		)		468.5				—				(260.5		)		260.5				—
	Cash received from (paid for) receivables purchased		462.6				(462.6		)		—				257.2				(257.2		)		—
	Interest on intercompany note received (paid)		0.1				(0.1		)		—				0.1				(0.1		)		—
	Year to Date	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
	30-Sep-13					Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(1,189.2	)		$	1,189.20			$	—			$	(652.2	)		$	652.2			$	—
	Gain (loss) on sale of accounts receivable (a)		(15.1		)		14.4				(0.7		)		(8.3		)		7.9				(1.1		)
	Servicing fees received (paid)		2				(2.0		)		—				1				(1.0		)		—
	Fees paid to outside investor		—				(0.9		)		(0.9		)		—				(0.5		)		(1.4		)
	Cash from customers (transferred) received		(1,150.8		)		1,150.80				—				(630.0		)		630				—
	Cash received from (paid for) receivables purchased		1,136.40				(1,136.4		)		—				622.1				(622.1		)		—
	Interest on intercompany note received (paid)		0.2				(0.2		)		—				0.1				(0.1		)		—
	Three Months Ended	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
	30-Sep-12					Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(472.6	)		$	472.6			$	—			$	(341.7	)		$	341.7			$	—
	Gain (loss) on sale of accounts receivable (a)		(6.0		)		5.8				(0.2		)		(4.3		)		3.4				(1.1		)
	Servicing fees received (paid)		0.8				(0.8		)		—				0.5				(0.5		)		—
	Fees paid to outside investor		—				(0.3		)		(0.3		)		—				(0.3		)		(0.6		)
	Cash from customers (transferred) received		(466.1		)		466.1				—				(267.8		)		267.8				—
	Cash received from (paid for) receivables purchased		460.4				(460.4		)		—				264.4				(264.4		)		—
	Interest on intercompany note received (paid)		0.2				(0.2		)		—				0.1				(0.1		)		—
	Year to Date	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
	30-Sep-12					Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(1,134.7	)		$	1,134.70			$	—			$	(433.4	)		$	433.4			$	—
	Gain (loss) on sale of accounts receivable (a)		(14.4		)		13.9				(0.5		)		(5.5		)		4.2				(1.8		)
	Servicing fees received (paid)		1.9				(1.9		)		—				0.6				(0.6		)		—
	Fees paid to outside investor		—				(0.9		)		(0.9		)		—				(0.4		)		(1.3		)
	Cash from customers (transferred) received		(1,112.7		)		1,112.70				—				(332.5		)		332.5				—
	Cash received from (paid for) receivables purchased		1,098.80				(1,098.8		)		—				328.3				(328.3		)		—
	Interest on intercompany note received (paid)		0.3				(0.3		)		—				0.1				(0.1		)		—
	(a) Any net gain (loss) is the result of the timing difference inherent in collecting receivables and over the life of the agreement will net to zero.

Nuclear_Plant_Tables

Nuclear Plant (Tables)	9 Months Ended
	Sep. 30, 2013
Nuclear Plant [Abstract]	'
Changes in nuclear decommissioning trust fund	'
	The following table summarizes the change in Great Plains Energy's and KCP&L's nuclear decommissioning trust fund.
		September 30					December 31
		2013					2012
	Decommissioning Trust		(millions)
	Beginning balance January 1		$	154.7				$	135.3
	Contributions		2.5					3.3
	Earned income, net of fees		1.9					3
	Net realized gains		1.6					1
	Net unrealized gains		12.1					12.1
	Ending balance		$	172.8				$	154.7
Detail of assets held in nuclear decommissioning trust fund	'
	The nuclear decommissioning trust is reported at fair value on the balance sheets and is invested in assets as detailed in the following table.
		September 30																		December 31
		2013																		2012
		Cost			Unrealized Gains						Unrealized					Fair			Cost			Unrealized			Unrealized				Fair
		Basis									Losses					Value			Basis			Gains			Losses				Value
		(millions)
	Equity securities	$	83.4			$	35.1					$	(1.0	)			$	117.5		$	80.6		$	21.1		$	(1.6	)		$	100.1
	Debt securities	49.8				2.8						(0.5		)			52.1			46.6			4.9			(0.1		)		51.4
	Other	3.2				—						—					3.2			3.2			—			—				3.2
	Total	$	136.4			$	37.9					$	(1.5	)			$	172.8		$	130.4		$	26		$	(1.7	)		$	154.7
Gains and losses from the sale of securities by the nuclear decommissioning trust fund	'
	The costs of securities sold are determined on the basis of specific identification.  The following table summarizes the realized gains and losses from the sale of securities in the nuclear decommissioning trust fund.
		Three Months Ended							Year to Date
		30-Sep							30-Sep
		2013			2012				2013				2012
		(millions)
	Realized gains	$	0.4		$	0.5			$	2.3			$	1.2
	Realized losses	(0.3		)	(0.1		)		(0.7		)		(0.3		)

Pension_Plans_and_Other_Employ1

Pension Plans and Other Employee Benefits (Tables)	9 Months Ended
	Sep. 30, 2013
Defined Benefit Plan Disclosure [Line Items]	'
Schedule of Net Benefit Costs [Table Text Block]	'
	The following tables provide Great Plains Energy's components of net periodic benefit costs prior to the effects of capitalization and sharing with joint owners of power plants.
		Pension Benefits						Other Benefits
	Three Months Ended September 30	2013			2012			2013			2012
	Components of net periodic benefit costs	(millions)
	Service cost	$	10.5		$	8.9		$	1.1		$	0.8
	Interest cost	11.8			12.2			1.9			1.9
	Expected return on plan assets	(11.8		)	(10.7		)	(0.5		)	(0.4		)
	Prior service cost	0.5			1.1			1.8			1.8
	Recognized net actuarial loss	13.7			11.1			0.5			—
	Transition obligation	—			—			—			0.3
	Net periodic benefit costs before regulatory adjustment	24.7			22.6			4.8			4.4
	Regulatory adjustment	(3.3		)	(3.9		)	(0.6		)	0.3
	Net periodic benefit costs	$	21.4		$	18.7		$	4.2		$	4.7
		Pension Benefits						Other Benefits
	Year to Date September 30	2013			2012			2013			2012
	Components of net periodic benefit costs	(millions)
	Service cost	$	31.5		$	26.6		$	3.3		$	2.4
	Interest cost	35.4			36.7			5.7			5.8
	Expected return on plan assets	(35.4		)	(32.1		)	(1.5		)	(1.3		)
	Prior service cost	1.5			3.3			5.4			5.4
	Recognized net actuarial loss	41.1			33.4			1.4			—
	Transition obligation	—			—			0.1			0.8
	Net periodic benefit costs before regulatory adjustment	74.1			67.9			14.4			13.1
	Regulatory adjustment	(9.7		)	(11.6		)	(1.7		)	1
	Net periodic benefit costs	$	64.4		$	56.3		$	12.7		$	14.1

Equity_Compensation_Tables

Equity Compensation (Tables)	9 Months Ended
	Sep. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Equity compensation expense and associated income tax benefits	'
	The following table summarizes Great Plains Energy's and KCP&L's equity compensation expense and the associated income tax benefit.
			Three Months Ended					Year to Date
			30-Sep					30-Sep
			2013		2012			2013		2012
	Great Plains Energy		(millions)
	Equity compensation expense		$	1.3	$	1.2		$	3.4	$	4
	Income tax benefit		0.4		0.4			1.1		1.7
	KCP&L
	Equity compensation expense		$	0.9	$	0.8		$	2.4	$	2.9
	Income tax benefit		0.3		0.3			0.7		1.3
Performance share activity	'
		Performance			Grant Date
		Shares			Fair Value*
	Beginning balance January 1, 2013		370,560			$	23.05
	Granted		226,967			24.17
	Earned		(104,453	)		23.37
	Forfeited		(11,523	)		22.82
	Performance adjustment		(51,542	)		23.37
	Ending balance September 30, 2013		430,009			23.52
	* weighted-average
Restricted stock activity	'
	Restricted stock activity is summarized in the following table.
		Nonvested			Grant Date
		Restricted Stock			Fair Value*
	Beginning balance January 1, 2013		277,439			$	19.03
	Granted and issued		75,745			22.46
	Vested		(64,405	)		17.88
	Forfeited		(4,142	)		21.44
	Ending balance September 30, 2013		284,637			20.14
	* weighted-average

LongTerm_Debt_Tables

Long-Term Debt (Tables)	9 Months Ended
	Sep. 30, 2013
Debt Disclosure [Abstract]	'
Schedule of Debt [Table Text Block]	'
	Great Plains Energy's and KCP&L's long-term debt is detailed in the following table.
			September 30				December 31
		Year Due	2013				2012
	KCP&L			(millions)
	General Mortgage Bonds
	2.95% EIRR bonds(a)	2015-2035		$	146.4			$	106.9
	7.15% Series 2009A (8.59% rate)(b)	2019		400				400
	4.65% EIRR Series 2005	2035		50				50
	5.375% Series 2007B			—				73.2
	Senior Notes
	5.85% Series (5.72% rate)(b)	2017		250				250
	6.375% Series (7.49% rate)(b)	2018		350				350
	3.15% Series	2023		300				—
	6.05% Series (5.78% rate)(b)	2035		250				250
	5.30% Series	2041		400				400
	EIRR Bonds
	0.07% Series 2007A and 2007B(c)	2035		146.5				—
	2.875% Series 2008	2038		23.4				23.4
	Other			—				2.6
	Current maturities			—				(0.4		)
	Unamortized discount			(4.2		)		(4.0		)
	Total KCP&L excluding current maturities			2,312.10				1,901.70
	Other Great Plains Energy
	GMO First Mortgage Bonds 9.44% Series	2014-2021		9				10.1
	GMO Pollution Control Bonds
	0.158% Wamego Series 1996(c)	2026		7.3				7.3
	0.158% State Environmental 1993(c)	2028		5				5
	5.85% SJLP Pollution Control			—				5.6
	GMO Senior Notes
	8.27% Series	2021		80.9				80.9
	3.49% Series A	2025		125				—
	4.06% Series B	2033		75				—
	4.74% Series C	2043		150				—
	GMO Medium Term Notes
	7.16% Series	2013		6				6
	7.33% Series	2023		3				3
	7.17% Series	2023		7				7
	Great Plains Energy Senior Notes
	6.875% Series (7.33% rate)(b)	2017		100				100
	4.85% Series (7.34% rate)(b)	2021		350				350
	5.292% Series	2022		287.5				287.5
	2.75% Series (3.67% rate)(b)			—				250
	Current maturities			(7.1		)		(262.7		)
	Unamortized discount and premium, net			5.1				5.4
	Total Great Plains Energy excluding current maturities			$	3,515.80			$	2,756.80
	(a)	Weighted-average interest rates at September 30, 2013
	(b)	Rate after amortizing gains/losses recognized in OCI on settlements of interest rate hedging instruments
	(c)	Variable rate

Related_Party_Transactions_and1

Related Party Transactions and Relationships (Tables)	9 Months Ended
	Sep. 30, 2013
Related Party Transactions [Abstract]	'
Schedule of related party receivables and payables	'
	The following table summarizes KCP&L's related party net receivables.
		September 30			December 31
			2013			2012
			(millions)
	Net receivable from GMO		$	23.6		$	26.2
	Net receivable from Great Plains Energy		16.8			13.8

Derivative_Instruments_Tables

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Values of open positions for derivative instruments [Table Text Block]	'
	The notional and recorded fair values of open positions for derivative instruments are summarized in the following table.  The fair values of these derivatives are recorded on the consolidated balance sheets.  The fair values below are gross values before netting agreements and netting of cash collateral.
		September 30								December 31
		2013								2012
		Notional				Fair				Notional			Fair
		Contract				Value				Contract			Value
		Amount								Amount
	Great Plains Energy	(millions)
	Futures contracts
	Cash flow hedges	$	—			$	—			$	1		$	(0.2	)
	Non-hedging derivatives	11				(1.2		)		17.9			(2.8		)
	Forward contracts
	Non-hedging derivatives	48.8				5.5				65.5			6.5
	Option contracts
	Non-hedging derivatives	3.2				0.5				—			—
	KCP&L
	Futures contracts
	Cash flow hedges	$	—			$	—			$	1		$	(0.2	)
Fair value of open derivative positions, gross values before netting agreements and netting of cash collatral [Table Text Block]	'
	The fair values of Great Plains Energy's and KCP&L's open derivative positions are summarized in the following tables.  The tables contain both derivative instruments designated as hedging instruments as well as non-hedging derivatives under GAAP.  The fair values below are gross values before netting agreements and netting of cash collateral.
	Great Plains Energy
		Balance Sheet		Asset Derivatives						Liability Derivatives
	September 30, 2013	Classification		Fair Value						Fair Value
	Derivatives Not Designated as Hedging Instruments				(millions)
	Commodity contracts	Derivative instruments			$	6					$	1.2
	December 31, 2012
	Derivatives Designated as Hedging Instruments
	Commodity contracts	Derivative instruments			$	—					$	0.2
	Derivatives Not Designated as Hedging Instruments
	Commodity contracts	Derivative instruments			6.5						2.8
	Total Derivatives				$	6.5					$	3
	KCP&L
		Balance Sheet		Asset Derivatives						Liability Derivatives
	December 31, 2012	Classification		Fair Value						Fair Value
	Derivatives Designated as Hedging Instruments				(millions)
	Commodity contracts	Derivative instruments			$	—					$	0.2
Offsetting Derivative Assets and Liabilities [Table Text Block]	'
	The following tables provide information regarding Great Plains Energy's and KCP&L's offsetting of derivative assets and liabilities.
	Great Plains Energy
																	Gross Amounts Not Offset in the Statement of Financial Position
	Description	Gross Amounts Recognized						Gross Amounts Offset in the Statement of Financial Position					Net Amounts Presented in the Statement of Financial Position				Financial Instruments				Cash Collateral Received			Net Amount
	30-Sep-13	(millions)
	Derivative assets		$	6					$	(0.1	)			$	5.9			$	—			$	—		$	5.9
	Derivative liabilities		1.2						(1.2		)			—				—				—			—
	31-Dec-12
	Derivative assets		$	6.5					$	—				$	6.5			$	—			$	—		$	6.5
	Derivative liabilities		3						(3.0		)			—				—				—			—
	KCP&L
																	Gross Amounts Not Offset in the Statement of Financial Position
	Description	Gross Amounts Recognized						Gross Amounts Offset in the Statement of Financial Position					Net Amounts Presented in the Statement of Financial Position				Financial Instruments				Cash Collateral Received			Net Amount
	31-Dec-12	(millions)
	Derivative liabilities		$	0.2					$	(0.2	)			$	—			$	—			$	—		$	—
Gain (loss) recognized in other comprehensive income or earnings for interest rate and commodity hedges [Table Text Block]	'
	The following tables summarize the amount of gain (loss) recognized in OCI or earnings for interest rate and commodity hedges.
	Great Plains Energy
	Derivatives in Cash Flow Hedging Relationship
								Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)
		Amount of Gain  (Loss) Recognized in OCI on Derivatives  (Effective Portion)						Income Statement Classification		Amount
	Three Months Ended September 30, 2013		(millions)							(millions)
	Interest rate contracts		$	—				Interest charges		$	(4.6	)
	Income tax benefit		—					Income tax benefit		1.8
	Total		$	—				Total		$	(2.8	)
	Year to Date September 30, 2013
	Interest rate contracts		$	—				Interest charges		$	(14.3	)
	Commodity contracts		—					Fuel		(0.2		)
	Income tax benefit		—					Income tax benefit		5.6
	Total		$	—				Total		$	(8.9	)
	Three Months Ended September 30, 2012
	Interest rate contracts		$	—				Interest charges		$	(5.0	)
	Commodity contracts		0.1					Fuel		(0.5		)
	Income tax expense		(0.1		)			Income tax benefit		2.1
	Total		$	—				Total		$	(3.4	)
	Year to Date September 30, 2012
	Interest rate contracts		$	—				Interest charges		$	(15.1	)
	Commodity contracts		(0.1		)			Fuel		(0.5		)
	Income tax benefit		—					Income tax benefit		6
	Total		$	(0.1	)			Total		$	(9.6	)
	KCP&L
	Derivatives in Cash Flow Hedging Relationship
								Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)
		Amount of Gain  (Loss) Recognized in OCI on Derivatives  (Effective Portion)						Income Statement Classification		Amount
	Three Months Ended September 30, 2013		(millions)							(millions)
	Interest rate contracts		$	—				Interest charges		$	(2.1	)
	Income tax benefit		—					Income tax benefit		0.7
	Total		$	—				Total		$	(1.4	)
	Year to Date September 30, 2013
	Interest rate contracts		$	—				Interest charges		$	(6.5	)
	Commodity contracts		—					Fuel		(0.2		)
	Income tax benefit		—					Income tax benefit		2.5
	Total		$	—				Total		$	(4.2	)
	Three Months Ended September 30, 2012
	Interest rate contracts		$	—				Interest charges		$	(2.2	)
	Commodity contracts		0.1					Fuel		(0.5		)
	Income tax expense		(0.1		)			Income tax benefit		1
	Total		$	—				Total		$	(1.7	)
	Year to Date September 30, 2012
	Interest rate contracts		$	—				Interest charges		$	(6.6	)
	Commodity contracts		(0.1		)			Fuel		(0.5		)
	Income tax benefit		—					Income tax benefit		2.7
	Total		$	(0.1	)			Total		$	(4.4	)
Gain (loss) recognized in a regulatory balance sheet account or earnings for utility commodity hedges [Table Text Block]	'
	The following table summarizes the amount of gain (loss) recognized in a regulatory asset or earnings for GMO utility commodity hedges.  GMO utility commodity derivatives fair value changes are recorded to either a regulatory asset or liability consistent with MPSC regulatory orders.
	Great Plains Energy
	Derivatives in Regulatory Account Relationship
								Gain (Loss) Reclassified from Regulatory Account
		Amount of Gain (Loss) Recognized in Regulatory Asset on Derivatives						Income Statement  Classification		Amount
	Three Months Ended September 30, 2013	(millions)								(millions)
	Commodity contracts		$	(0.1	)			Fuel		$	(0.3	)
	Total		$	(0.1	)			Total		$	(0.3	)
	Year to Date September 30, 2013
	Commodity contracts		$	0.8				Fuel		$	(1.5	)
	Total		$	0.8				Total		$	(1.5	)
	Three Months Ended September 30, 2012
	Commodity contracts		$	0.9				Fuel		$	(2.8	)
	Total		$	0.9				Total		$	(2.8	)
	Year to Date September 30, 2012
	Commodity contracts		$	(1.8	)			Fuel		$	(5.5	)
	Total		$	(1.8	)			Total		$	(5.5	)
Accumulated other comprehensive income related to cash flow hedges [Table Text Block]	'
	The amounts recorded in accumulated OCI related to the cash flow hedges are summarized in the following table.
		Great Plains Energy											KCP&L
		September 30						December 31					September 30				December 31
		2013						2012					2013				2012
			(millions)
	Current assets		$	10					$	10.6				$	10			$	10.6
	Current liabilities		(53.3		)				(68.4		)			(45.5		)		(52.8		)
	Noncurrent liabilities		—						(0.1		)			—				(0.1		)
	Deferred income taxes		16.8						22.5					13.9				16.5
	Total		$	(26.5	)				$	(35.4	)			$	(21.6	)		$	(25.8	)

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2013
Fair Value Disclosures [Abstract]	'
Fair value of assets and liabilities	'
	The following tables include Great Plains Energy's and KCP&L's balances of financial assets and liabilities measured at fair value on a recurring basis.
												Fair Value Measurements Using
		September 30										Quoted Prices in Active Markets for Identical Assets			Significant Other Observable Inputs				Significant Unobservable Inputs
		2013										(Level 1)			(Level 2)				(Level 3)
	Description							Netting(d)
	KCP&L		(millions)
	Assets
	Nuclear decommissioning trust (a)
	Equity securities		$	117.5					$	—			$	117.5		$	—			$	—
	Debt securities
	U.S. Treasury		20.8						—				20.8			—				—
	U.S. Agency		2.4						—				—			2.4				—
	State and local obligations		3.2						—				—			3.2				—
	Corporate bonds		25.1						—				—			25.1				—
	Foreign governments		0.6						—				—			0.6				—
	Cash equivalents		5.3						—				—			5.3				—
	Other		(2.1		)				—				—			(2.1		)		—
	Total nuclear decommissioning trust		172.8						—				138.3			34.5				—
	Total		$	172.8					$	—			$	138.3		$	34.5			$	—
	Other Great Plains Energy
	Assets
	Derivative instruments (b)		$	5.9					$	(0.1	)		$	—		$	4.4			$	1.6
	SERP rabbi trusts (c)
	Equity securities		0.1						—				0.1			—				—
	Fixed income funds		18.7						—				—			18.7				—
	Total SERP rabbi trusts		18.8						—				0.1			18.7				—
	Total		24.7						(0.1		)		0.1			23.1				1.6
	Liabilities
	Derivative instruments (b)		—						(1.2		)		1.2			—				—
	Total		$	—					$	(1.2	)		$	1.2		$	—			$	—
	Great Plains Energy
	Assets
	Nuclear decommissioning trust (a)		$	172.8					$	—			$	138.3		$	34.5			$	—
	Derivative instruments (b)		5.9						(0.1		)		—			4.4				1.6
	SERP rabbi trusts (c)		18.8						—				0.1			18.7				—
	Total		197.5						(0.1		)		138.4			57.6				1.6
	Liabilities
	Derivative instruments (b)		—						(1.2		)		1.2			—				—
	Total		$	—					$	(1.2	)		$	1.2		$	—			$	—
												Fair Value Measurements Using
	Description	December 31						Netting(d)				Quoted Prices in Active Markets for Identical Assets			Significant Other Observable Inputs				Significant Unobservable Inputs
		2012										(Level 1)			(Level 2)				(Level 3)
	KCP&L		(millions)
	Assets
	Nuclear decommissioning trust (a)
	Equity securities		$	100.1					$	—			$	100.1		$	—			$	—
	Debt securities
	U.S. Treasury		18.5						—				18.5			—				—
	U.S. Agency		2.8						—				—			2.8				—
	State and local obligations		3.3						—				—			3.3				—
	Corporate bonds		26.8						—				—			26.8				—
	Other		0.3						—				—			0.3				—
	Total nuclear decommissioning trust		151.8						—				118.6			33.2				—
	Total		151.8						—				118.6			33.2				—
	Liabilities
	Derivative instruments (b)		—						(0.2		)		0.2			—				—
	Total		$	—					$	(0.2	)		$	0.2		$	—			$	—
	Other Great Plains Energy
	Assets
	Derivative instruments (b)		$	6.5					$	—			$	—		$	4.2			$	2.3
	SERP rabbi trusts (c)
	Equity securities		0.1						—				0.1			—				—
	Fixed income funds		20.2						—				—			20.2				—
Total SERP rabbi trusts		20.3						—				0.1			20.2				—
Total		26.8						—				0.1			24.4				2.3
Liabilities
Derivative instruments (b)		—						(2.8		)		2.8			—				—
Total		$	—					$	(2.8	)		$	2.8		$	—			$	—
Great Plains Energy
Assets
Nuclear decommissioning trust (a)		$	151.8					$	—			$	118.6		$	33.2			$	—
Derivative instruments (b)		6.5						—				—			4.2				2.3
SERP rabbi trusts (c)		20.3						—				0.1			20.2				—
Total		178.6						—				118.7			57.6				2.3
Liabilities
Derivative instruments (b)		—						(3.0		)		3			—				—
Total		$	—					$	(3.0	)		$	3		$	—			$	—
(a)	Fair value is based on quoted market prices of the investments held by the fund and/or valuation models.  The total does not include $2.9 million of cash and cash equivalents at December 31, 2012.
(b)	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.
(c)	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.
(d)	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 September 30, 2013, and December 31, 2012, Great Plains Energy netted $1.1 million and $3.0 million, respectively, of cash collateral posted with counterparties.
Unobservable inputs reconciliation	'
	The following tables reconcile the beginning and ending balances for all Level 3 assets measured at fair value on a recurring basis.
	Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
		Derivative Instruments
		2013				2012
		(millions)
	Balance at July 1	$	1.9			$	2.2
	Total realized/unrealized gains included in non-operating income	1				3.7
	Settlements	(1.3		)		(3.5		)
	Balance at September 30	$	1.6			$	2.4
	Total unrealized gains (losses) included in non-operating income relating to assets
	still on the consolidated balance sheet at September 30	$	(0.3	)		$	0.3
	Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
		Derivative Instruments
		2013				2012
		(millions)
	Balance at January 1	$	2.3			$	3.1
	Total realized/unrealized gains included in non-operating income	5.3				4.8
	Settlements	(6.0		)		(5.5		)
	Balance at September 30	$	1.6			$	2.4
	Total unrealized losses included in non-operating income relating to assets
	still on the consolidated balance sheet at September 30	$	(0.4	)		$	(0.4	)

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Abstract]	'
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	'
	The following tables reflect the change in the balances of each component of accumulated other comprehensive loss for Great Plains Energy and KCP&L.
	Great Plains Energy
		Gains and Losses on Cash Flow Hedges(a)				Defined Benefit Pension Items(a)				Total(a)
		(millions)
	Beginning balance January 1, 2013		$	(35.4	)		$	(3.0	)	$	(38.4	)
	Amounts reclassified from accumulated other comprehensive loss		8.9				0.3			9.2
	Net current period other comprehensive income		8.9				0.3			9.2
	Ending balance September 30, 2013		$	(26.5	)		$	(2.7	)	$	(29.2	)
	(a) Net of tax
	KCP&L
		Gains and Losses on Cash Flow Hedges(a)
		(millions)
	Beginning balance January 1, 2013		$	(25.8	)
	Amounts reclassified from accumulated other comprehensive loss		4.2
	Net current period other comprehensive income		4.2
	Ending balance September 30, 2013		$	(21.6	)
	(a) Net of tax
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]	'
	The following tables reflect the effect on certain line items of net income from amounts reclassified out of each component of accumulated other comprehensive loss for Great Plains Energy and KCP&L.
	Great Plains Energy
	Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Loss				Affected Line Item in the Income Statement
	Three Months Ended September 30, 2013	(millions)
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts		$	(4.6	)	Interest charges
			(4.6		)	Income before income tax expense and loss from equity investments
			1.8			Income tax benefit
			$	(2.8	)	Net income
	Amortization of defined benefit pension items
	Net losses included in net periodic benefit costs		$	(0.1	)	Utility operating and maintenance expenses
			(0.1		)	Income before income tax expense and loss from equity investments
			—			Income tax benefit
			(0.1		)	Net income
	Total reclassifications, net of tax		$	(2.9	)	Net income
	Year to Date September 30, 2013
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts		$	(14.3	)	Interest charges
	Commodity contracts		(0.2		)	Fuel
			(14.5		)	Income before income tax expense and loss from equity investments
			5.6			Income tax benefit
			$	(8.9	)	Net income
	Amortization of defined benefit pension items
	Net losses included in net periodic benefit costs		$	(0.4	)	Utility operating and maintenance expenses
			(0.4		)	Income before income tax expense and loss from equity investments
			0.1			Income tax benefit
			(0.3		)	Net income
	Total reclassifications, net of tax		$	(9.2	)	Net income
	KCP&L
	Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Loss				Affected Line Item in the Income Statement
	Three Months Ended September 30, 2013	(millions)
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts		$	(2.1	)	Interest charges
			(2.1		)	Income before income tax expense
			0.7			Income tax benefit
	Total reclassifications, net of tax		$	(1.4	)	Net income
	Year to Date September 30, 2013
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts		$	(6.5	)	Interest charges
	Commodity contracts		(0.2		)	Fuel
			(6.7		)	Income before income tax expense
			2.5			Income tax benefit
	Total reclassifications, net of tax		$	(4.2	)	Net income

Taxes_Tables

Taxes (Tables)	9 Months Ended
	Sep. 30, 2013
Income Tax Disclosure [Abstract]	'
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	'
	Components of income tax expense are detailed in the following tables.
		Three Months Ended								Year to Date
		30-Sep								30-Sep
	Great Plains Energy	2013				2012				2013			2012
	Current income taxes	(millions)
	Federal	$	1			$	(1.4	)		$	1		$	(4.7	)
	State	(0.4		)		(0.3		)		(0.3		)	—
	Total	0.6				(1.7		)		0.7			(4.7		)
	Deferred income taxes
	Federal	67.9				75.1				105.4			97.6
	State	13.3				13.9				21.3			18.2
	Total	81.2				89				126.7			115.8
	Noncurrent income taxes
	Federal	—				—				—			(0.2		)
	State	—				—				(0.2		)	—
	Foreign	0.1				(4.1		)		(0.2		)	(4.2		)
	Total	0.1				(4.1		)		(0.4		)	(4.4		)
	Investment tax credit
	Deferral	0.3				—				0.3			—
	Amortization	(0.4		)		(0.6		)		(1.3		)	(1.8		)
	Total	(0.1		)		(0.6		)		(1.0		)	(1.8		)
	Income tax expense	$	81.8			$	82.6			$	126		$	104.9
		Three Months Ended								Year to Date
		30-Sep								30-Sep
	KCP&L	2013				2012				2013			2012
	Current income taxes	(millions)
	Federal	$	(0.6	)		$	22.9			$	(1.2	)	$	23.1
	State	(0.4		)		4.1				(0.5		)	4.2
	Total	(1.0		)		27				(1.7		)	27.3
	Deferred income taxes
	Federal	55				22.7				75.6			38.8
	State	10.9				4.5				15.9			8.6
	Total	65.9				27.2				91.5			47.4
	Noncurrent income taxes
	Federal	(10.1		)		1				(9.0		)	1.1
	State	(1.7		)		0.2				(1.5		)	0.2
	Total	(11.8		)		1.2				(10.5		)	1.3
	Investment tax credit
	Deferral	0.3				—				0.3			—
	Amortization	(0.3		)		(0.5		)		(0.8		)	(1.4		)
	Total	—				(0.5		)		(0.5		)	(1.4		)
	Income tax expense	$	53.1			$	54.9			$	78.8		$	74.6
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	'
	Effective Income Tax Rates
	Effective income tax rates reflected in the financial statements and the reasons for their differences from the statutory federal rates are detailed in the following tables.
		Three Months Ended						Year to Date
		30-Sep						30-Sep
	Great Plains Energy	2013			2012			2013			2012
	Federal statutory income tax rate	35	%		35	%		35	%		35	%
	Differences between book and tax depreciation not normalized	(0.5	)		0.5			(0.2	)		1.1
	Amortization of investment tax credits	(0.2	)		(0.3	)		(0.4	)		(0.6	)
	Federal income tax credits	(1.6	)		(1.0	)		(2.8	)		(2.8	)
	State income taxes	3.7			3.8			3.8			3.9
	Changes in uncertain tax positions, net	0.1			(1.8	)		(0.1	)		(1.4	)
	Other	(0.1	)		(0.1	)		(0.2	)		(0.3	)
	Effective income tax rate	36.4	%		36.1	%		35.1	%		34.9	%
		Three Months Ended						Year to Date
		30-Sep						30-Sep
	KCP&L	2013			2012			2013			2012
	Federal statutory income tax rate	35	%		35	%		35	%		35	%
	Differences between book and tax depreciation not normalized	(0.9	)		0.7			(0.6	)		1.3
	Amortization of investment tax credits	(0.2	)		(0.3	)		(0.3	)		(0.6	)
	Federal income tax credits	(2.2	)		(1.5	)		(4.2	)		(4.0	)
	State income taxes	3.8			3.9			3.8			4
	Changes in uncertain tax positions, net	0.1			—			—			—
	Other	(0.1	)		—			(0.2	)		(0.3	)
	Effective income tax rate	35.5	%		37.8	%		33.5	%		35.4	%
Summary of Income Tax Contingencies [Table Text Block]	'
	The following table reflects activity for Great Plains Energy and KCP&L related to the liability for unrecognized tax benefits.
			Great Plains Energy											KCP&L
		September 30						December 31					September 30				December 31
		2013						2012					2013				2012
			(millions)
	Beginning balance January 1		$	21.4					$	24				$	10.5			$	8.7
	Additions for current year tax positions		—						3.7					—				3.6
	Reductions for current year tax positions		(0.3		)				—					—				—
	Reductions for prior year tax positions		(10.5		)				(1.8		)			(10.5		)		(1.6		)
	Statute expirations		(0.2		)				(4.7		)			—				(0.2		)
	Foreign currency translation adjustments		(0.2		)				0.2					—				—
	Ending balance		$	10.2					$	21.4				$	—			$	10.5

Segments_and_Related_Informati1

Segments and Related Information (Tables)	9 Months Ended
	Sep. 30, 2013
Segment Reporting [Abstract]	'
Segment Financial Information [Table Text Block]	'
	The following tables reflect summarized financial information concerning Great Plains Energy's reportable segment.
	Three Months Ended	Electric				Other				Eliminations				Great Plains
	30-Sep-13	Utility												Energy
		(millions)
	Operating revenues		$	765			$	—			$	—			$	765
	Depreciation and amortization		(73.3		)		—				—				(73.3		)
	Interest charges		(46.7		)		(13.6		)		11.4				(48.9		)
	Income tax (expense) benefit		(83.6		)		1.8				—				(81.8		)
	Net income (loss) attributable to Great Plains Energy		145.4				(2.3		)		—				143.1
	Year to Date	Electric				Other				Eliminations				Great Plains
	30-Sep-13	Utility												Energy
		(millions)
	Operating revenues		$	1,907.50			$	—			$	—			$	1,907.50
	Depreciation and amortization		(216.1		)		—				—				(216.1		)
	Interest charges		(141.9		)		(42.7		)		36.6				(148.0		)
	Income tax (expense) benefit		(130.1		)		4.1				—				(126.0		)
	Net income (loss) attributable to Great Plains Energy		238.5				(5.8		)		—				232.7
	Three Months Ended	Electric				Other				Eliminations				Great Plains
	30-Sep-12	Utility												Energy
		(millions)
	Operating revenues		$	746.2			$	—			$	—			$	746.2
	Depreciation and amortization		(68.9		)		—				—				(68.9		)
	Interest charges		(48.4		)		(12.3		)		12.6				(48.1		)
	Income tax (expense) benefit		(86.5		)		3.9				—				(82.6		)
	Net income attributable to Great Plains Energy		141.9				4.3				—				146.2
	Year to Date	Electric				Other				Eliminations				Great Plains
	30-Sep-12	Utility												Energy
		(millions)
	Operating revenues		$	1,829.50			$	—			$	—			$	1,829.50
	Depreciation and amortization		(204.2		)		—				—				(204.2		)
	Interest charges		(149.5		)		(52.5		)		31.2				(170.8		)
	Income tax (expense) benefit		(120.6		)		15.7				—				(104.9		)
	Net income (loss) attributable to Great Plains Energy		210.2				(15.0		)		—				195.2
		Electric				Other				Eliminations				Great Plains
		Utility												Energy
	September 30, 2013		(millions)
	Assets		$	10,193.90			$	87.8			$	(412.5	)		$	9,869.20
	Capital expenditures(a)		486.2				—				—				486.2
	December 31, 2012
	Assets		$	9,910.60			$	122.4			$	(385.7	)		$	9,647.30
	Capital expenditures(a)		610.2				—				—				610.2
	(a) Capital expenditures reflect year to date amounts for the periods presented.

Summary_of_Significant_Account3

Summary of Significant Accounting Policies Summary of Significant Accounting Policies Utility Plant (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Utility Plant, at original cost	'	'
Public Utilities, Property, Plant and Equipment, Plant in Service	$11,480.70	$11,160.50
Kansas City Power and Light Company [Member]	'	'
Utility Plant, at original cost	'	'
Public Utilities, Property, Plant and Equipment, Plant in Service	$8,198.80	$7,971.40

Summary_of_Significant_Account4

Summary of Significant Accounting Policies Earnings Per Share (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income [Abstract]	'	'	'	'
Net income (loss)	$143.10	$146.40	$232.70	$195.20
Less: net income (loss) attributable to noncontrolling interest	0	0.2	0	0
Less: preferred stock dividend requirements	0.4	0.4	1.2	1.2
Earnings (loss) available for common shareholders	$142.70	$145.80	$231.50	$194
Common Shares Outstanding [Abstract]	'	'	'	'
Average number of common shares outstanding (in shares)	153.6	153.2	153.5	142.9
Add: effect of dilutive securities (in shares)	0.2	0.2	0.2	2.1
Diluted average number of common shares outstanding (in shares)	153.8	153.4	153.7	145
Earnings Per Share [Abstract]	'	'	'	'
Earnings Per Share, Basic	$0.93	$0.95	$1.51	$1.36
Earnings Per Share, Diluted	$0.93	$0.95	$1.51	$1.34

Summary_of_Significant_Account5

Summary of Significant Accounting Policies Antidilutive Securities (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Performance Shares [Member]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	54,660	192,723	54,660	209,000
Restricted Stock [Member]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	2,531	21,652	2,531

Summary_of_Significant_Account6

Summary of Significant Accounting Policies Subsequent Events (Details) (Dividend Declared [Member], USD $)	9 Months Ended
	Sep. 30, 2013	Nov. 05, 2013
Kansas City Power and Light Company [Member]	'	'
Dividends Declared [Abstract]	'	'
Dividends Payable, Amount Per Share	'	$23,000,000
Subsequent Event, Description	'KCPs Board of Directors declared a cash dividend payable to Great Plains Energy	'
Common Stock [Member]	'	'
Dividends Declared [Abstract]	'	'
Dividends Payable, Amount Per Share	'	$0.23
Subsequent Event, Description	'Great Plains Energy's Board of Directors (Board) declared a quarterly dividend	'
Preferred Stock [Member]	'	'
Dividends Declared [Abstract]	'	'
Subsequent Event, Description	'The Board also declared regular dividends on Great Plains Energy's preferred stock	'

Supplemental_Cash_Flow_Informa2

Supplemental Cash Flow Information (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Cash flows affected by changes in:	'	'
Receivables	($44.10)	$12.50
Accounts receivable pledged as collateral	-16	-95
Fuel inventories	11.2	-5.4
Materials and supplies	-4.3	-7.8
Accounts payable	-91.5	-49.4
Accrued taxes	81	65.4
Accrued interest	18.4	-16.6
Deferred refueling outage costs	-21.8	13.4
Pension and post-retirement benefit obligations	40.2	21.9
Allowance for equity funds used during construction	-9.1	-0.3
Fuel recovery mechanism	-5.3	13.1
Uncertain tax positions	-0.4	-4.4
Other operating activities	-8.4	-14.2
Total other operating activities	-50.1	-66.8
Cash paid during the period:	'	'
Interest Paid, Net	111.3	185.4
Income Taxes Paid	0.1	3.3
Non-cash investing activities:	'	'
Liabilities accrued for capital expenditures	34.5	52.2
Kansas City Power and Light Company [Member]	'	'
Cash flows affected by changes in:	'	'
Receivables	-40.2	-35.1
Accounts receivable pledged as collateral	0	-15
Fuel inventories	10.4	-6.2
Materials and supplies	-3	-6.1
Accounts payable	-66.7	-18
Accrued taxes	55.3	76.5
Accrued interest	12.2	9.8
Deferred refueling outage costs	-21.8	13.4
Pension and post-retirement benefit obligations	41.9	24.7
Allowance for equity funds used during construction	-9.1	-0.3
Fuel recovery mechanism	-1.2	-0.9
Uncertain tax positions	-10.5	1.2
Other operating activities	-6.1	-20.6
Total other operating activities	-38.8	23.4
Cash paid during the period:	'	'
Interest Paid, Net	73.2	77.3
Income Taxes Paid	0	0
Non-cash investing activities:	'	'
Liabilities accrued for capital expenditures	$28.30	$48

Receivables_Accounts_Notes_and

Receivables Accounts, Notes, and Financing (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Allowance for doubtful accounts	($3.40)	($2.60)
Other Receivables, Gross, Current	88.4	98.8
Receivables, net	199.1	154.5
Kansas City Power and Light Company [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Allowance for doubtful accounts	-1.9	-1.5
Other Receivables, Gross, Current	80.3	81.8
Receivables, net	207.3	163.2
Trade Accounts Receivable [Member] | Billed Revenues [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Accounts Receivable, Gross, Current	24.4	0
Trade Accounts Receivable [Member] | Billed Revenues [Member] | Kansas City Power and Light Company [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Accounts Receivable, Gross, Current	23.8	0
Trade Accounts Receivable [Member] | Unbilled Revenues [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Accounts Receivable, Gross, Current	89.7	58.3
Trade Accounts Receivable [Member] | Unbilled Revenues [Member] | Kansas City Power and Light Company [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Accounts Receivable, Gross, Current	64.7	42.9
Intercompany Receivables [Member] | Kansas City Power and Light Company [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Accounts Receivable, Gross, Current	$40.40	$40

Receivables_Narrative_Details

Receivables Narrative (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts receivable pledged as collateral	$190	$174
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	190	174
Kansas City Power and Light Company [Member]	'	'
Accounts receivable pledged as collateral	110	110
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	110	110
Contractually Specified Servicing Fees Percentage Amount	1.50%	'
Maximum amount of outstanding principal under receivables agreement	110	'
KCPL Greater Missouri Operations [Member]	'	'
Contractually Specified Servicing Fees Percentage Amount	1.25%	'
Maximum amount of outstanding principal under receivables agreement from June 1 to October 31 of each year	80	'
Maximum amount of outstanding principal under receivables agreement from November 1 to May 31 of each year	$65	'

Receivables_Details

Receivables (Details) (USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Accounts Receivable Sold [Line Items]	'		'		'		'
Receivables (sold) purchased	$0		$0		$0		$0
Gain (Loss) on Sale of Accounts Receivable	-0.5	[1]	-1.1	[1]	-1.1	[1]	-1.8	[1]
Servicing fees received (paid)	0		0		0		0
Fees paid to outside investor	-0.5		-0.6		-1.4		-1.3
Cash from customers (transferred) received	0		0		0		0
Cash received from (paid for) receivables purchased	0		0		0		0
Intercompany Interest Income (Expense) On Notes	0		0		0		0
Kansas City Power and Light Company [Member]	'		'		'		'
Accounts Receivable Sold [Line Items]	'		'		'		'
Receivables (sold) purchased	0		0		0		0
Gain (Loss) on Sale of Accounts Receivable	-0.3	[1]	-0.2	[1]	-0.7	[1]	-0.5	[1]
Servicing fees received (paid)	0		0		0		0
Fees paid to outside investor	-0.3		-0.3		-0.9		-0.9
Cash from customers (transferred) received	0		0		0		0
Cash received from (paid for) receivables purchased	0		0		0		0
Intercompany Interest Income (Expense) On Notes	0		0		0		0
Kansas City Power And Light Company Unconsolidated [Member]	'		'		'		'
Accounts Receivable Sold [Line Items]	'		'		'		'
Receivables (sold) purchased	-481.2		-472.6		-1,189.20		-1,134.70
Gain (Loss) on Sale of Accounts Receivable	-6.1	[1]	-6	[1]	-15.1	[1]	-14.4	[1]
Servicing fees received (paid)	0.8		0.8		2		1.9
Fees paid to outside investor	0		0		0		0
Cash from customers (transferred) received	-468.5		-466.1		-1,150.80		-1,112.70
Cash received from (paid for) receivables purchased	462.6		460.4		1,136.40		1,098.80
Intercompany Interest Income (Expense) On Notes	0.1		0.2		0.2		0.3
KCPL Receivables Company [Member]	'		'		'		'
Accounts Receivable Sold [Line Items]	'		'		'		'
Receivables (sold) purchased	481.2		472.6		1,189.20		1,134.70
Gain (Loss) on Sale of Accounts Receivable	5.8	[1]	5.8	[1]	14.4	[1]	13.9	[1]
Servicing fees received (paid)	-0.8		-0.8		-2		-1.9
Fees paid to outside investor	-0.3		-0.3		-0.9		-0.9
Cash from customers (transferred) received	468.5		466.1		1,150.80		1,112.70
Cash received from (paid for) receivables purchased	-462.6		-460.4		-1,136.40		-1,098.80
Intercompany Interest Income (Expense) On Notes	-0.1		-0.2		-0.2		-0.3
KCPL Greater Missouri Operations [Member]	'		'		'		'
Accounts Receivable Sold [Line Items]	'		'		'		'
Receivables (sold) purchased	-264.1		-341.7		-652.2		-433.4
Gain (Loss) on Sale of Accounts Receivable	-3.4	[1]	-4.3	[1]	-8.3	[1]	-5.5	[1]
Servicing fees received (paid)	0.4		0.5		1		0.6
Fees paid to outside investor	0		0		0		0
Cash from customers (transferred) received	-260.5		-267.8		-630		-332.5
Cash received from (paid for) receivables purchased	257.2		264.4		622.1		328.3
Intercompany Interest Income (Expense) On Notes	0.1		0.1		0.1		0.1
GMO Receivables Company Member	'		'		'		'
Accounts Receivable Sold [Line Items]	'		'		'		'
Receivables (sold) purchased	264.1		341.7		652.2		433.4
Gain (Loss) on Sale of Accounts Receivable	3.2	[1]	3.4	[1]	7.9	[1]	4.2	[1]
Servicing fees received (paid)	-0.4		-0.5		-1		-0.6
Fees paid to outside investor	-0.2		-0.3		-0.5		-0.4
Cash from customers (transferred) received	260.5		267.8		630		332.5
Cash received from (paid for) receivables purchased	-257.2		-264.4		-622.1		-328.3
Intercompany Interest Income (Expense) On Notes	($0.10)		($0.10)		($0.10)		($0.10)
[1]	Any net gain (loss) is the result of the timing difference inherent in collecting receivables and over the life of the agreement will net to zero.

Nuclear_Plant_Details

Nuclear Plant (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Investments in decommissioning trust fund [Line Items]	'	'	'	'	'	'
Cost Basis	$136.40	'	$136.40	'	$130.40	'
Gross Unrealized Gains	'	'	37.9	'	26	'
Gross Unrealized Losses	'	'	-1.5	'	-1.7	'
Fair Value, Nuclear decommissioning trust fund	172.8	'	172.8	'	154.7	135.3
Weighted average maturity of debt securities (in years)	7	'	7	'	'	'
Realized Gains on investments in decommissioning trust fund	0.4	0.5	2.3	1.2	'	'
Realized Losses on investments in decommissioning trust fund	-0.3	-0.1	-0.7	-0.3	'	'
Equity Securities [Member]	'	'	'	'	'	'
Investments in decommissioning trust fund [Line Items]	'	'	'	'	'	'
Cost Basis	83.4	'	83.4	'	80.6	'
Gross Unrealized Gains	'	'	35.1	'	21.1	'
Gross Unrealized Losses	'	'	-1	'	-1.6	'
Fair Value, Nuclear decommissioning trust fund	117.5	'	117.5	'	100.1	'
Debt Securities [Member]	'	'	'	'	'	'
Investments in decommissioning trust fund [Line Items]	'	'	'	'	'	'
Cost Basis	49.8	'	49.8	'	46.6	'
Gross Unrealized Gains	'	'	2.8	'	4.9	'
Gross Unrealized Losses	'	'	-0.5	'	-0.1	'
Fair Value, Nuclear decommissioning trust fund	52.1	'	52.1	'	51.4	'
Other Securities [Member]	'	'	'	'	'	'
Investments in decommissioning trust fund [Line Items]	'	'	'	'	'	'
Cost Basis	3.2	'	3.2	'	3.2	'
Gross Unrealized Gains	'	'	0	'	0	'
Gross Unrealized Losses	'	'	0	'	0	'
Fair Value, Nuclear decommissioning trust fund	3.2	'	3.2	'	3.2	'
Kansas City Power and Light Company [Member]	'	'	'	'	'	'
Investments in decommissioning trust fund [Line Items]	'	'	'	'	'	'
Fair Value, Nuclear decommissioning trust fund	$172.80	'	$172.80	'	$154.70	'

Nuclear_Plant_Decommissioning_

Nuclear Plant Decommissioning Trust (Details) (USD $)	9 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Nuclear decommissioning trust fund [Roll Forward]	'	'
Nuclear decommissioning trust fund, beginning balance	$154.70	$135.30
Contributions to nuclear decommissioning trust fund	2.5	3.3
Nuclear decommissioning trust fund earned income, net of fees	1.9	3
Net realized gains (losses) on nuclear decommissioning trust fund	1.6	1
Net unrealized gains (losses) on nuclear decommissioning trust fund	12.1	12.1
Nuclear decommissioning trust fund, ending balance	172.8	154.7
Kansas City Power and Light Company [Member]	'	'
Nuclear decommissioning trust fund [Roll Forward]	'	'
Nuclear decommissioning trust fund, ending balance	$172.80	$154.70
Kansas City Power and Light Company [Member] | Wolf Creek [Member]	'	'
Jointly Owned Utility Plant Interests [Line Items]	'	'
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	47.00%	'

Pension_Plans_and_Other_Employ2

Pension Plans and Other Employee Benefits (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Amounts recognized in the consolidated balance sheets [Abstract]	'	'	'	'	'
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities	($2.80)	'	($2.80)	'	($2.80)
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	-554.6	'	-554.6	'	-557.5
Other Changes In Plan Assets And Benefit Obligations Recognized In Other Comprehensive Income Regulatory Assets/Liabilities [Abstract]	'	'	'	'	'
Amortization of net losses included in net periodic benefit costs	0.1	0.1	0.4	0.3	'
Kansas City Power and Light Company [Member]	'	'	'	'	'
Amounts recognized in the consolidated balance sheets [Abstract]	'	'	'	'	'
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities	-1.4	'	-1.4	'	-1.4
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	-531.9	'	-531.9	'	-534.5
Pension Plans, Defined Benefit [Member]	'	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'	'
Defined Benefit Plan, Contributions by Employer	'	'	40.2	'	'
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year	'	'	17.2	'	'
Components of net periodic benefit costs [Abstract]	'	'	'	'	'
Service cost	10.5	8.9	31.5	26.6	'
Interest cost	11.8	12.2	35.4	36.7	'
Defined Benefit Plan, Expected Return on Plan Assets	-11.8	-10.7	-35.4	-32.1	'
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	0.5	1.1	1.5	3.3	'
Defined Benefit Plan, Amortization of Gains (Losses)	13.7	11.1	41.1	33.4	'
Defined Benefit Plan, Amortization of Transition Obligations (Assets)	0	0	0	0	'
Net periodic benefit costs before regulatory adjustment	24.7	22.6	74.1	67.9	'
Defined benefit plan, regulatory adjustment	-3.3	-3.9	-9.7	-11.6	'
Defined Benefit Plan, Net Periodic Benefit Cost	21.4	18.7	64.4	56.3	'
Other Postretirement Benefit Plan, Defined Benefit [Member]	'	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'	'
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year	'	'	18.7	'	'
Components of net periodic benefit costs [Abstract]	'	'	'	'	'
Service cost	1.1	0.8	3.3	2.4	'
Interest cost	1.9	1.9	5.7	5.8	'
Defined Benefit Plan, Expected Return on Plan Assets	-0.5	-0.4	-1.5	-1.3	'
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	1.8	1.8	5.4	5.4	'
Defined Benefit Plan, Amortization of Gains (Losses)	0.5	0	1.4	0	'
Defined Benefit Plan, Amortization of Transition Obligations (Assets)	0	0.3	0.1	0.8	'
Net periodic benefit costs before regulatory adjustment	4.8	4.4	14.4	13.1	'
Defined benefit plan, regulatory adjustment	-0.6	0.3	-1.7	1	'
Defined Benefit Plan, Net Periodic Benefit Cost	$4.20	$4.70	$12.70	$14.10	'

Equity_Compensation_Details

Equity Compensation (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'		'
Equity compensation expense	$1,300,000		$1,200,000	$3,400,000		$4,000,000
Income tax benefit	400,000		400,000	1,100,000		1,700,000
Performance Shares [Member]	'		'	'		'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'		'
Expected volatility	'		'	19.00%		'
Expected dividend yield	'		'	3.88%		'
Risk-free interest rate	'		'	0.35%		'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]	'		'	'		'
Beginning balance (in shares)	'		'	370,560		'
Granted (in shares)	'		'	226,967		'
Earned (in shares)	'		'	-104,453		'
Forfeited (in shares)	'		'	-11,523		'
Performance adjustment (in shares)	'		'	-51,542		'
Ending balance (in shares)	430,009		'	430,009		'
Weighted average beginning balance (in dollars per share)	'		'	$23.05	[1]	'
Weighted average granted (in dollars per share)	$24.33		$18.12	$24.17	[1]	$19.02
Weighted average earned (in dollars per share)	'		'	$23.37	[1]	'
Weighted average forfeited (in dollars per share)	'		'	$22.82	[1]	'
Weighted average performance adjustment (in dollars per share)	'		'	$23.37	[1]	'
Weighted average ending balance (in dollars per share)	$23.52	[1]	'	$23.52	[1]	'
Total unrecognized compensation expense	4,300,000		'	4,300,000		'
Remaining weighted-average contractual term (in years)	'		'	'1 year 7 months		'
Fair value of performance shares earned and paid	'		'	2,400,000		0
Restricted Stock [Member]	'		'	'		'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]	'		'	'		'
Beginning balance (in shares)	'		'	277,439		'
Granted (in shares)	'		'	75,745		'
Forfeited (in shares)	'		'	-4,142		'
Vested (in shares)	'		'	-64,405		'
Ending balance (in shares)	284,637		'	284,637		'
Weighted average beginning balance (in dollars per share)	'		'	$19.03	[1]	'
Weighted average granted (in dollars per share)	$22.65		$22.18	$22.46	[1]	$19.73
Weighted average vested (in dollars per share)	'		'	$17.88	[1]	'
Weighted average forfeited (in dollars per share)	'		'	$21.44	[1]	'
Weighted average ending balance (in dollars per share)	$20.14	[1]	'	$20.14	[1]	'
Total unrecognized compensation expense	2,600,000		'	2,600,000		'
Total fair value of shares vested	600,000		'	1,200,000		3,300,000
Remaining weighted-average contractual term (in years)	'		'	'1 year 5 months		'
Kansas City Power and Light Company [Member]	'		'	'		'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'		'
Equity compensation expense	900,000		800,000	2,400,000		2,900,000
Income tax benefit	$300,000		$300,000	$700,000		$1,300,000
[1]	* weighted-average

Shortterm_Borrowings_and_Short1

Short-term Borrowings and Short-term Bank Lines of Credit (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Short-term Debt [Line Items]	'	'
Amount of outstanding cash borrowings	$6	$12
Commercial paper outstanding	53	530.1
Parent Company [Member] | Revolving Credit Facility [Member]	'	'
Short-term Debt [Line Items]	'	'
Amount of revolving credit facility	200	'
Revolving credit facility expiration date	1-Dec-16	'
Maximum borrowing capacity with transfer of unused commitments	400	'
Covenant term - amount considered in default	50	'
Covenant Term Ratio of Consolidated Indebtedness to Consolidated Capitalization Ratio, Maximum	0.65	'
Line of Credit Facility, Covenant Compliance	'in compliance	'
Amount of outstanding cash borrowings	6	12
Weighted-average interest rate from outstanding borrowings	1.94%	2.00%
Amount of letters of credit outstanding	1.8	1.8
Kansas City Power and Light Company [Member]	'	'
Short-term Debt [Line Items]	'	'
Commercial paper outstanding	23.7	361
Kansas City Power and Light Company [Member] | Revolving Credit Facility [Member]	'	'
Short-term Debt [Line Items]	'	'
Amount of revolving credit facility	600	'
Revolving credit facility expiration date	1-Dec-16	'
Maximum transfer of unused commitments	200	'
Covenant term - amount considered in default	50	'
Covenant Term Ratio of Consolidated Indebtedness to Consolidated Capitalization Ratio, Maximum	0.65	'
Line of Credit Facility, Covenant Compliance	'in compliance	'
Amount of outstanding cash borrowings	0	0
Commercial paper outstanding	23.7	361
Weighted-average interest rate from outstanding borrowings	0.27%	0.48%
Amount of letters of credit outstanding	3.8	13.9
KCPL Greater Missouri Operations [Member] | Revolving Credit Facility [Member]	'	'
Short-term Debt [Line Items]	'	'
Amount of revolving credit facility	450	'
Revolving credit facility expiration date	1-Dec-16	'
Maximum transfer of unused commitments	200	'
Covenant term - amount considered in default	50	'
Covenant Term Ratio of Consolidated Indebtedness to Consolidated Capitalization Ratio, Maximum	0.65	'
Line of Credit Facility, Covenant Compliance	'in compliance	'
Amount of outstanding cash borrowings	0	0
Commercial paper outstanding	29.3	169.1
Weighted-average interest rate from outstanding borrowings	0.66%	0.94%
Amount of letters of credit outstanding	$14.60	$15.10

Shortterm_Borrowings_and_Short2

Short-term Borrowings and Short-term Bank Lines of Credit Subsequent Events (Details) (Revolving Credit Facility [Member])	9 Months Ended			0 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Oct. 02, 2013	Oct. 02, 2013	Oct. 02, 2013
	Parent Company [Member]	Kansas City Power and Light Company [Member]	KCPL Greater Missouri Operations [Member]	Subsequent Event [Member]	Subsequent Event [Member]	Subsequent Event [Member]
				Parent Company [Member]	Kansas City Power and Light Company [Member]	KCPL Greater Missouri Operations [Member]
Subsequent Event [Line Items]	'	'	'	'	'	'
Revolving credit facility expiration date	1-Dec-16	1-Dec-16	1-Dec-16	1-Oct-18	1-Oct-18	1-Oct-18
Subsequent Event, Description	'	'	'	'In October 2013, Great Plains Energy entered into an amendment to its $200 million revolving credit facility with a group of banks to extend the term to October 2018 from December 2016.	'In October 2013, KCP&L entered into an amendment to its $600 million revolving credit facility with a group of banks that provides support for its issuance of commercial paper and other general corporate purposes to extend the term to October 2018 from December 2016.	'In October 2013, GMO entered into an amendment to its $450 million revolving credit facility with a group of banks that provides support for its issuance of commercial paper and other general corporate purposes to extend the term to October 2018 from December 2016.

LongTerm_Debt_Details

Long-Term Debt (Details) (USD $)	9 Months Ended
	Sep. 30, 2013		Dec. 31, 2012
Debt Instrument [Line Items]	'		'
Current maturities	($7,100,000)		($263,100,000)
Long-term debt excluding current maturities	3,515,800,000		2,756,800,000
Kansas City Power and Light Company [Member]	'		'
Debt Instrument [Line Items]	'		'
Current maturities	0		-400,000
Unamortized discount	-4,200,000		-4,000,000
Long-term debt excluding current maturities	2,312,100,000		1,901,700,000
Kansas City Power and Light Company [Member] | Secured Debt [Member] | General Mortgage bonds EIRR due 2015-2035 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	146,400,000		106,900,000
Debt Instrument Maturity Date Range Start	31-Dec-15		'
Debt Instrument Maturity Date Range End	31-Dec-35		'
Long-term Debt, Weighted Average Interest Rate	2.95%	[1]	'
Kansas City Power and Light Company [Member] | Secured Debt [Member] | General Mortgage bonds Series 2009 due 2019 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	400,000,000		400,000,000
Debt Instrument, Maturity Date	31-Dec-19		'
Interest rates (in hundredths)	7.15%		'
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	8.59%	[2]	'
Kansas City Power and Light Company [Member] | Secured Debt [Member] | General Mortgage bonds EIRR series 2005 due 2035 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	50,000,000		50,000,000
Debt Instrument, Maturity Date	31-Dec-35		'
Interest rates (in hundredths)	4.65%		'
Kansas City Power and Light Company [Member] | Secured Debt [Member] | General Mortgage bonds EIRR series 2007B due 2035 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	0		73,200,000
Interest rates (in hundredths)	5.38%		'
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior notes due 2017 KCPL [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	250,000,000		250,000,000
Debt Instrument, Maturity Date	31-Dec-17		'
Interest rates (in hundredths)	5.85%		'
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	5.72%	[2]	'
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior notes due 2018 KCPL [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	350,000,000		350,000,000
Debt Instrument, Maturity Date	31-Dec-18		'
Interest rates (in hundredths)	6.38%		'
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	7.49%	[2]	'
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior Notes due 2023 KCPL [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	300,000,000		0
Debt Instrument, Maturity Date	31-Dec-23		'
Interest rates (in hundredths)	3.15%		'
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior notes due 2035 KCPL [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	250,000,000		250,000,000
Debt Instrument, Maturity Date	31-Dec-35		'
Interest rates (in hundredths)	6.05%		'
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	5.78%	[2]	'
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior Notes Due 2041 KCPL [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	400,000,000		400,000,000
Debt Instrument, Maturity Date	31-Dec-41		'
Interest rates (in hundredths)	5.30%		'
Kansas City Power and Light Company [Member] | Unsecured Debt [Member] | EIRR Bonds Series 2007A and 2007B due 2035 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	146,500,000		0
Debt Instrument, Maturity Date	31-Dec-35		'
Variable rate (in hundredths)	0.07%	[3]	'
Kansas City Power and Light Company [Member] | Unsecured Debt [Member] | EIRR bonds 2.875 percent Series 2008 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	23,400,000		23,400,000
Debt Instrument, Maturity Date	31-Dec-38		'
Interest rates (in hundredths)	2.88%		'
Kansas City Power and Light Company [Member] | Other Debt [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	0		2,600,000
KCPL Greater Missouri Operations [Member] | Secured Debt [Member] | First Mortgage Bonds due through 2021 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	9,000,000		10,100,000
Debt Instrument Maturity Date Range Start	31-Dec-14		'
Debt Instrument Maturity Date Range End	31-Dec-21		'
Interest rates (in hundredths)	9.44%		'
KCPL Greater Missouri Operations [Member] | Senior Notes [Member]	'		'
GMO Senior Notes [Abstract]	'		'
Debt Instrument, Covenant Description	'GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the agreement, not greater than 0.65 to 1.00 at all times. In addition, GMO's priority debt, as defined in the agreement, cannot exceed 15% of consolidated tangible net worth, as defined in the agreement.		'
Debt Instrument, Covenant Compliance	'in compliance		'
KCPL Greater Missouri Operations [Member] | Senior Notes [Member] | Senior notes 8.27 percent series due 2021 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	80,900,000		80,900,000
Debt Instrument, Maturity Date	31-Dec-21		'
Interest rates (in hundredths)	8.27%		'
KCPL Greater Missouri Operations [Member] | Senior Notes [Member] | Senior Notes Series A due 2025 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	125,000,000		0
Debt Instrument, Maturity Date	31-Dec-25		'
Interest rates (in hundredths)	3.49%		'
KCPL Greater Missouri Operations [Member] | Senior Notes [Member] | Senior Notes Series B due 2033 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	75,000,000		0
Debt Instrument, Maturity Date	31-Dec-33		'
Interest rates (in hundredths)	4.06%		'
KCPL Greater Missouri Operations [Member] | Senior Notes [Member] | Senior Notes Series C due 2043 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	150,000,000		0
Debt Instrument, Maturity Date	31-Dec-43		'
Interest rates (in hundredths)	4.74%		'
KCPL Greater Missouri Operations [Member] | Medium-term Notes [Member] | Medium term notes 7.16 percent series due 2013 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	6,000,000		6,000,000
Debt Instrument, Maturity Date	31-Dec-13		'
Interest rates (in hundredths)	7.16%		'
KCPL Greater Missouri Operations [Member] | Medium-term Notes [Member] | Medium term notes 7.33 percent series due 2023 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	3,000,000		3,000,000
Debt Instrument, Maturity Date	31-Dec-23		'
Interest rates (in hundredths)	7.33%		'
KCPL Greater Missouri Operations [Member] | Medium-term Notes [Member] | Medium term notes 7.17 percent series due 2023 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	7,000,000		7,000,000
Debt Instrument, Maturity Date	31-Dec-23		'
Interest rates (in hundredths)	7.17%		'
KCPL Greater Missouri Operations [Member] | Unsecured Debt [Member] | Pollution control bonds Wamego Series 1996 due 2026 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	7,300,000		7,300,000
Debt Instrument, Maturity Date	31-Dec-26		'
Variable rate (in hundredths)	0.16%	[3]	'
KCPL Greater Missouri Operations [Member] | Unsecured Debt [Member] | Pollution control bonds state environmental 1993 due 2028 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	5,000,000		5,000,000
Debt Instrument, Maturity Date	31-Dec-28		'
Variable rate (in hundredths)	0.16%	[3]	'
KCPL Greater Missouri Operations [Member] | Unsecured Debt [Member] | Pollution control bonds SJLP due 2013 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	0		5,600,000
Interest rates (in hundredths)	5.85%		'
Parent Company [Member] | Senior Notes [Member] | Senior notes due 2013 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	0		250,000,000
Interest rates (in hundredths)	2.75%		'
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	3.67%	[2]	'
Parent Company [Member] | Senior Notes [Member] | Senior notes due 2017 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	100,000,000		100,000,000
Debt Instrument, Maturity Date	31-Dec-17		'
Interest rates (in hundredths)	6.88%		'
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	7.33%	[2]	'
Parent Company [Member] | Senior Notes [Member] | Senior Notes Due 2021 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	350,000,000		350,000,000
Debt Instrument, Maturity Date	31-Dec-21		'
Interest rates (in hundredths)	4.85%		'
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	7.34%	[2]	'
Parent Company [Member] | Senior Notes [Member] | Senior Notes Due 2022 [Member]	'		'
Debt Instrument [Line Items]	'		'
Principal outstanding	287,500,000		287,500,000
Debt Instrument, Maturity Date	31-Dec-22		'
Interest rates (in hundredths)	5.29%		'
Other Consolidated Entities [Member]	'		'
Debt Instrument [Line Items]	'		'
Current maturities	-7,100,000		-262,700,000
Unarmortized discount and premium, net	$5,100,000		$5,400,000
[1]	Weighted-average interest rates at SeptemberB 30, 2013
[2]	Rate after amortizing gains/losses recognized in OCI on settlements of interest rate hedging instruments
[3]	Variable rate

LongTerm_Debt_LongTerm_Debt_Re

Long-Term Debt Long-Term Debt Remarketed (Details) (Kansas City Power and Light Company [Member], USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
Secured Debt [Member] | Secured 1992 Series EIRR Bonds [Member]	'
EIRR Bonds Remarketed	$31
EIRR Bonds Remarketed Maturity Date	31-Dec-17
EIRR Bonds Remarketed Interest Rate Stated Percentage	1.25%
EIRR Bonds Remarketed Interest Rate Terms	'fixed rate
Secured Debt [Member] | Secured Series 1993B EIRR Bonds Member	'
EIRR Bonds Remarketed No Longer Held	39.5
EIRR Bonds Remarketed Maturity Date	31-Dec-23
EIRR Bonds Remarketed Interest Rate Stated Percentage	2.95%
EIRR Bonds Remarketed Interest Rate Terms	'fixed rate
Secured Debt [Member] | Secured Series 1993A Bonds [Member]	'
EIRR Bonds Remarketed	40
EIRR Bonds Remarketed Maturity Date	31-Dec-23
EIRR Bonds Remarketed Interest Rate Stated Percentage	2.95%
EIRR Bonds Remarketed Interest Rate Terms	'fixed rate
Secured Debt [Member] | Mortgage Bonds Series 2007 EIRR Insurer due 2035 [Member]	'
Extinguishment of Debt, Amount	146.5
Unsecured Debt [Member] | General Mortgage bonds EIRR Series 2007A-1 due 2035 [Member]	'
EIRR Bonds Remarketed No Longer Held	10
Unsecured Debt [Member] | General Mortgage bonds EIRR series 2007A-2 due 2035 [Member]	'
EIRR Bonds Remarketed No Longer Held	63.3
Unsecured Debt [Member] | Remarketed EIRR Bonds Series 2007A due 2035 [Member]	'
EIRR Bonds Remarketed No Longer Held	73.3
EIRR Bonds Remarketed Maturity Date	31-Dec-35
EIRR Bonds Remarketed Interest Rate Terms	'variable rate that will be determined weekly
Unsecured Debt [Member] | Remarketed EIRR Bonds Series 2007B due 2035 [Member]	'
EIRR Bonds Remarketed	73.2
EIRR Bonds Remarketed Maturity Date	31-Dec-35
EIRR Bonds Remarketed Interest Rate Terms	'variable rate that will be determined weekly
Unsecured Debt [Member] | EIRR bonds 2.875 percent Series 2008 [Member]	'
EIRR Bonds Remarketed	$23.40
EIRR Bonds Remarketed Maturity Date	31-Dec-38
EIRR Bonds Remarketed Interest Rate Stated Percentage	2.88%
EIRR Bonds Remarketed Interest Rate Terms	'fixed rate

Commitments_and_Contingencies_

Commitments and Contingencies Environmental Matters (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified	MW
	T
Estimates Of Environmental Financial Impact And Related Issues [Line Items]	'	'
Current estimate of capital expenditures final regulations	$700	'
Current estimate of capital expenditures for proposed regulations, minimum	600	'
Current estimate of capital expenditures for proposed regulations, maximum	800	'
Clean Air Interstate Rule (CAIR) and Cross-State Air Pollution Rule (CSAPR) [Abstract]	'	'
Number Of States Required To Reduce Emissions Under Cair	28	'
Mercury and Air Toxics Standards Rule [Abstract]	'	'
Capacity of electric steam generating units that fall under MACT standards (in megawatts)	25	'
SO2 National Ambient Air Quality Standard (NAAQS) [Abstract]	'	'
Primary one-hour sulfur dioxide standard, as revised June 2010 (in parts per million)	0.075	'
Primary twenty-four hour sulfur dioxide standard, prior to June 2010 (in parts per million)	0.14	'
Primary one-year sulfur dioxide standard, prior to June 2010 (in parts per million)	0.03	'
Climate Change [Abstract]	'	'
CO2 produced per year (in tons)	25,000,000	'
Remediation [Abstract]	'	'
Amount accrued for future investigation remediation and of GMO retained liabilities	2	2
LaCygne Station [Member]	'	'
Best Available Retrofit Technology Rule [Abstract]	'	'
Predetermination request for environmental equipment required at LaCygne Station to comply with BART	1,230	'
Kansas City Power and Light Company [Member]	'	'
Estimates Of Environmental Financial Impact And Related Issues [Line Items]	'	'
Current estimate of capital expenditures final regulations	700	'
Cash capital expenditures incurred for La Cygne environmental project	344	'
Current estimate of capital expenditures for proposed regulations, minimum	350	'
Current estimate of capital expenditures for proposed regulations, maximum	450	'
Climate Change [Abstract]	'	'
CO2 produced per year (in tons)	19,000,000	'
Minimum required renewable energy generation capacity percentage in Kansas by 2011	10.00%	'
Minimum required renewable energy generation capacity percentage in Kansas by 2016	15.00%	'
Minimum required renewable energy generation capacity percentage in Kansas by 2020	20.00%	'
Minimum required renewable energy generation capacity percentage in Missouri by 2011	2.00%	'
Minimum required renewable energy generation capacity percentage in Missouri by 2014	5.00%	'
Minimum required renewable energy generation capacity percentage in Missouri by 2018	10.00%	'
Minimum required renewable energy generation capacity percentage in Missouri by 2021	15.00%	'
Estimated electricity required to come from solar resources (in megawatts)	2	'
Remediation [Abstract]	'	'
Accrued environmental remediation expenses	0.3	0.3
Kansas City Power and Light Company [Member] | LaCygne Station [Member]	'	'
Best Available Retrofit Technology Rule [Abstract]	'	'
Predetermination request for environmental equipment required at LaCygne Station to comply with BART	615	'
Entity's ownership percentage in facility (in hundredths)	50.00%	'
KCPL Greater Missouri Operations [Member]	'	'
Climate Change [Abstract]	'	'
Minimum required renewable energy generation capacity percentage in Missouri by 2011	2.00%	'
Minimum required renewable energy generation capacity percentage in Missouri by 2014	5.00%	'
Minimum required renewable energy generation capacity percentage in Missouri by 2018	10.00%	'
Minimum required renewable energy generation capacity percentage in Missouri by 2021	15.00%	'
Estimated electricity required to come from solar resources (in megawatts)	2	'
Remediation [Abstract]	'	'
Estimated amount of insurance proceeds available to cover qualified remediation expenses	2.6	'
KCPL Greater Missouri Operations [Member] | Jeffrey Units Nos 1 and 2 [Member]	'	'
Best Available Retrofit Technology Rule [Abstract]	'	'
Entity's ownership percentage in facility (in hundredths)	8.00%	'
Westar Energy Inc [Member] | Jeffrey Units Nos 1 and 2 [Member]	'	'
Best Available Retrofit Technology Rule [Abstract]	'	'
Entity's ownership percentage in facility (in hundredths)	92.00%	'
New Source Review [Abstract]	'	'
Estimated cost to install a selective catalytic reduction system at Jeffrey Energy Center pursuant to a settlement agreement	$240	'

Legal_Proceedings_Loss_Conting

Legal Proceedings Loss Contingencies (Details) (Pending Litigation [Member], KCPL Greater Missouri Operations [Member], USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
Pending Litigation [Member] | KCPL Greater Missouri Operations [Member]	'
Loss Contingencies [Line Items]	'
Approximate amount of refunds received as a net purchaser of power through settlements with sellers of power	$8
Estimated additional refunds entitled to receive	$12

Related_Party_Transactions_and2

Related Party Transactions and Relationships (Details) (Kansas City Power and Light Company [Member], USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
KCPL Greater Missouri Operations [Member]	'	'	'	'	'
Related Party Transaction [Line Items]	'	'	'	'	'
Receivable from Related Party	$23.60	'	$23.60	'	$26.20
KCPL employees manage GMO's business and operate its facilities at cost	32.7	23.9	82.3	76.8	'
KCPL net wholesale sales to GMO	9.6	6.3	19.6	19.1	'
Great Plains Energy [Member]	'	'	'	'	'
Related Party Transaction [Line Items]	'	'	'	'	'
Receivable from Related Party	16.8	'	16.8	'	13.8
Money pool payable	'	'	'	'	$3.80

Derivative_Instruments_Details

Derivative Instruments (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Futures contracts [Member] | Cash Flow Hedging [Member]	'	'
Price Risk Derivatives [Abstract]	'	'
Notional Contract Amount	$0	$1
Fair Value	0	-0.2
Futures contracts [Member] | Not Designated as Hedging Instrument [Member]	'	'
Price Risk Derivatives [Abstract]	'	'
Notional Contract Amount	11	17.9
Fair Value	-1.2	-2.8
Forward Contracts [Member] | Not Designated as Hedging Instrument [Member]	'	'
Price Risk Derivatives [Abstract]	'	'
Notional Contract Amount	48.8	65.5
Fair Value	5.5	6.5
Option contracts [Member] | Not Designated as Hedging Instrument [Member]	'	'
Price Risk Derivatives [Abstract]	'	'
Notional Contract Amount	3.2	0
Fair Value	0.5	0
Kansas City Power and Light Company [Member]	'	'
Price Risk Derivatives [Abstract]	'	'
Percentage of projected natural gas usage hedged year one	0.00%	'
Kansas City Power and Light Company [Member] | Futures contracts [Member] | Cash Flow Hedging [Member]	'	'
Price Risk Derivatives [Abstract]	'	'
Notional Contract Amount	0	1
Fair Value	$0	($0.20)
KCPL Greater Missouri Operations [Member]	'	'
Price Risk Derivatives [Abstract]	'	'
Percentage of expected on peak natural gas and natural gas equivalent purchased power price exposure hedged year two	28.00%	'
Percentage of expected on peak natural gas and natural gas equivalent purchased power price exposure hedged year three	5.00%	'

Derivative_Instruments_Fair_Va

Derivative Instruments Fair Value (Details) (USD $)	Sep. 30, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Derivatives, Fair Value [Line Items]	'		'
Accumulated Other Comprehensive Income (Loss), Net of Tax	($29.20)	[1]	($38.40)	[1]
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Accumulated Other Comprehensive Income (Loss), Net of Tax	-26.5	[1]	-35.4	[1]
Kansas City Power and Light Company [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Accumulated Other Comprehensive Income (Loss), Net of Tax	-21.6		-25.8
Kansas City Power and Light Company [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Accumulated Other Comprehensive Income (Loss), Net of Tax	-21.6	[1]	-25.8	[1]
Derivative [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Derivative asset, fair value, amount not offset against collateral	'		6.5
Derivative liability, fair value, amount not offset against collateral	'		3
Current assets [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Accumulated Other Comprehensive Income (Loss), before Tax	10		10.6
Current assets [Member] | Kansas City Power and Light Company [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Accumulated Other Comprehensive Income (Loss), before Tax	10		10.6
Current liabilities [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Accumulated Other Comprehensive Income (Loss), before Tax	-53.3		-68.4
Current liabilities [Member] | Kansas City Power and Light Company [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Accumulated Other Comprehensive Income (Loss), before Tax	-45.5		-52.8
Noncurrent liabilities [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Accumulated Other Comprehensive Income (Loss), before Tax	0		-0.1
Noncurrent liabilities [Member] | Kansas City Power and Light Company [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Accumulated Other Comprehensive Income (Loss), before Tax	0		-0.1
Deferred income taxes [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Accumulated Other Comprehensive Income (Loss), before Tax	16.8		22.5
Deferred income taxes [Member] | Kansas City Power and Light Company [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Accumulated Other Comprehensive Income (Loss), before Tax	13.9		16.5
Commodity Contract [Member] | Designated as Hedging Instrument [Member] | Derivative [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Derivative asset, fair value, amount not offset against collateral	'		0
Derivative liability, fair value, amount not offset against collateral	'		0.2
Commodity Contract [Member] | Designated as Hedging Instrument [Member] | Derivative [Member] | Kansas City Power and Light Company [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Derivative asset, fair value, amount not offset against collateral	'		0
Derivative liability, fair value, amount not offset against collateral	'		0.2
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member] | Derivative [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Derivative asset, fair value, amount not offset against collateral	6		6.5
Derivative liability, fair value, amount not offset against collateral	$1.20		$2.80
[1]	Net of tax

Derivative_Instruments_by_Hedg

Derivative Instruments by Hedging Relationship by Income Statement Location (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Cash Flow Hedging [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	$0	$0	$0	($0.10)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	-2.8	-3.4	-8.9	-9.6
Cash Flow Hedging [Member] | Kansas City Power and Light Company [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	0	0	0	-0.1
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	-1.4	-1.7	-4.2	-4.4
Cash Flow Hedging [Member] | Interest charges [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	-4.6	-5	-14.3	-15.1
Cash Flow Hedging [Member] | Interest charges [Member] | Kansas City Power and Light Company [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	-2.1	-2.2	-6.5	-6.6
Cash Flow Hedging [Member] | Fuel Costs [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	'	-0.5	-0.2	-0.5
Cash Flow Hedging [Member] | Fuel Costs [Member] | Kansas City Power and Light Company [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	'	-0.5	-0.2	-0.5
Cash Flow Hedging [Member] | Income tax benefit (expense) [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	1.8	2.1	5.6	6
Cash Flow Hedging [Member] | Income tax benefit (expense) [Member] | Kansas City Power and Light Company [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	0.7	1	2.5	2.7
Regulatory Account [Member] | Fuel Costs [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gain(Loss) Reclassified from Regulatory Account into Income (Effective Portion)	-0.3	-2.8	-1.5	-5.5
Interest Rate Contract [Member] | Cash Flow Hedging [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	0	0	0	0
Interest Rate Contract [Member] | Cash Flow Hedging [Member] | Kansas City Power and Light Company [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	0	0	0	0
Commodity Contract [Member] | Cash Flow Hedging [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	'	0.1	0	-0.1
Commodity Contract [Member] | Cash Flow Hedging [Member] | Kansas City Power and Light Company [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	'	0.1	0	-0.1
Commodity Contract [Member] | Regulatory Account [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized on Regulatory Account on Derivatives (Effective Portion)	-0.1	0.9	0.8	-1.8
Income tax benefit (expense) [Member] | Cash Flow Hedging [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	0	-0.1	0	0
Income tax benefit (expense) [Member] | Cash Flow Hedging [Member] | Kansas City Power and Light Company [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	$0	($0.10)	$0	$0

Derivative_Instruments_Gain_an

Derivative Instruments Gain and Losses (Details) (Not Designated as Hedging Instrument [Member], Commodity [Member], USD $)	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2013
			Kansas City Power and Light Company [Member]	Kansas City Power and Light Company [Member]
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	$0.10	($1)	$0.40	$1

Derivative_Instruments_Cash_Fl

Derivative Instruments Cash Flow Hedge (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
Derivative [Line Items]	'
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	($17.10)
Kansas City Power and Light Company [Member]	'
Derivative [Line Items]	'
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	($8.70)

Derivative_Instruments_Derivat

Derivative Instruments Derivative Instruments Offsetting (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Derivative Assets [Abstract]	'	'
Derivative Asset, Fair Value, Gross Asset	$6	$6.50
Derivative Asset, Fair Value, Gross Amounts Offset	-0.1	0
Derivative Assets, Fair Value, Net	5.9	6.5
Derivative, Collateral, Obligation to Return Securities	0	0
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative Assets Net of Gross Amounts Offset And Not Offset	5.9	6.5
Derivative Liabilities [Abstract]	'	'
Derivative Liability, Fair Value, Gross Liability	1.2	3
Derivative Liability, Fair Value, Gross Amounts Offset	-1.2	-3
Derivative Liabilities, Fair Value, Net	0	0
Derivative, Collateral, Right to Reclaim Securities	0	0
Derivative, Collateral, Right to Reclaim Cash	0	0
Derivative Liability, Fair Value, Net of Gross Amounts Offset And Not Offset	0	0
Kansas City Power and Light Company [Member]	'	'
Derivative Liabilities [Abstract]	'	'
Derivative Liability, Fair Value, Gross Liability	'	0.2
Derivative Liability, Fair Value, Gross Amounts Offset	'	-0.2
Derivative Liabilities, Fair Value, Net	'	0
Derivative, Collateral, Right to Reclaim Securities	'	0
Derivative, Collateral, Right to Reclaim Cash	'	0
Derivative Liability, Fair Value, Net of Gross Amounts Offset And Not Offset	'	$0

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	Sep. 30, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Assets [Abstract]	'		'
Derivative instruments, assets	$5.90		$6.50
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	0		0
Kansas City Power and Light Company [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Cash and cash equivalents from nuclear decommissioning trust	'		2.9
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	'		0
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	5.9	[1]	6.5	[1]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	172.8	[2]	151.8	[2]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	18.8	[3]	20.3	[3]
Total assets	197.5		178.6
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	0	[1]	0	[1]
Total liabilities	0		0
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	1.1		3
Assets [Abstract]	'		'
Derivative instruments, assets	-0.1	[1],[4]	0	[1],[4]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[2],[4]	0	[2],[4]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0	[3],[4]	0	[3],[4]
Total assets	-0.1	[4]	0	[4]
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	-1.2	[1],[4]	-3	[1],[4]
Total liabilities	-1.2	[4]	-3	[4]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	0	[1]	0	[1]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	138.3	[2]	118.6	[2]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0.1	[3]	0.1	[3]
Total assets	138.4		118.7
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	1.2	[1]	3	[1]
Total liabilities	1.2		3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	4.4	[1]	4.2	[1]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	34.5	[2]	33.2	[2]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	18.7	[3]	20.2	[3]
Total assets	57.6		57.6
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	0	[1]	0	[1]
Total liabilities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	1.6	[1]	2.3	[1]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[2]	0	[2]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0	[3]	0	[3]
Total assets	1.6		2.3
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] | Estimate of Fair Value Measurement [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	172.8	[2]	151.8	[2]
SERP rabbi trust [Abstract]	'		'
Total assets	172.8		151.8
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	'		0	[1]
Total liabilities	'		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	117.5		100.1
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	20.8		18.5
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	2.4		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	3.2		3.3
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	25.1		26.8
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	0.6		'
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	5.3		'
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	-2.1		0.3
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[2],[4]	0	[2],[4]
SERP rabbi trust [Abstract]	'		'
Total assets	0	[4]	0	[4]
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	'		-0.2	[1],[4]
Total liabilities	'		-0.2	[4]
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	[4]	0	[4]
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	[4]	0	[4]
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	[4]	0	[4]
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	[4]	0	[4]
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	[4]	0	[4]
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	[4]	'
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	[4]	'
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	[4]	0	[4]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	138.3	[2]	118.6	[2]
SERP rabbi trust [Abstract]	'		'
Total assets	138.3		118.6
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	'		0.2	[1]
Total liabilities	'		0.2
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	117.5		100.1
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	20.8		18.5
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		'
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	0		'
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
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	34.5	[2]	33.2	[2]
SERP rabbi trust [Abstract]	'		'
Total assets	34.5		33.2
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	'		0	[1]
Total liabilities	'		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
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	2.4		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	3.2		3.3
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	25.1		26.8
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	0.6		'
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	5.3		'
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	-2.1		0.3
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[2]	0	[2]
SERP rabbi trust [Abstract]	'		'
Total assets	0		0
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	'		0	[1]
Total liabilities	'		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
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		'
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		'
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
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Estimate of Fair Value Measurement [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	5.9	[1]	6.5	[1]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	18.8	[3]	20.3	[3]
Total assets	24.7		26.8
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	0	[1]	0	[1]
Total liabilities	0		0
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	18.7		20.2
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Netting [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	-0.1	[1],[4]	0	[1],[4]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0	[3],[4]	0	[3],[4]
Total assets	-0.1	[4]	0	[4]
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	-1.2	[1],[4]	-2.8	[1],[4]
Total liabilities	-1.2	[4]	-2.8	[4]
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	[4]	0	[4]
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	[4]	0	[4]
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 1 [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	0	[1]	0	[1]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0.1	[3]	0.1	[3]
Total assets	0.1		0.1
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	1.2	[1]	2.8	[1]
Total liabilities	1.2		2.8
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	4.4	[1]	4.2	[1]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	18.7	[3]	20.2	[3]
Total assets	23.1		24.4
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	0	[1]	0	[1]
Total liabilities	0		0
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	18.7		20.2
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 3 [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	1.6	[1]	2.3	[1]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0	[3]	0	[3]
Total assets	1.6		2.3
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	0	[1]	0	[1]
Total liabilities	0		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.
[2]	Fair value is based on quoted market prices of the investments held by the fund and/or valuation models. The total does not include $2.9 million of cash and cash equivalents at DecemberB 31, 2012.
[3]	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.
[4]	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 SeptemberB 30, 2013, and DecemberB 31, 2012, Great Plains Energy netted $1.1 million and $3.0 million, respectively, of cash collateral posted with counterparties.

Fair_Value_Measurements_Level_

Fair Value Measurements Level 3 (Details) (Derivative Financial Instruments, Assets [Member], USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Derivative Financial Instruments, Assets [Member]	'	'	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Balance at beginning of period	$1.90	$2.20	$2.30	$3.10
Total realized/unrealized gains or (losses) included in non-operating income	1	3.7	5.3	4.8
Settlements	-1.3	-3.5	-6	-5.5
Balance at end of period	1.6	2.4	1.6	2.4
Total unrealized gains and (losses) included in non-operating income relating to assets and liabilities still on the consolidated balance sheet at period end	($0.30)	$0.30	($0.40)	($0.40)

Fair_Value_Measurements_Fair_V

Fair Value Measurements Fair Value Long-Term Debt (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Billions, unless otherwise specified
Carrying (Reported) Amount, Fair Value Disclosure [Member]	'	'
Fair value of financial instruments [Abstract]	'	'
Long-term Debt	$3.50	$3
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Kansas City Power and Light Company [Member]	'	'
Fair value of financial instruments [Abstract]	'	'
Long-term Debt	2.3	1.9
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]	'	'
Fair value of financial instruments [Abstract]	'	'
Long-term debt fair value	3.7	3.5
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Kansas City Power and Light Company [Member]	'	'
Fair value of financial instruments [Abstract]	'	'
Long-term debt fair value	$2.50	$2.20

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Income (Loss) (Details) (USD $)	3 Months Ended			9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]	'		'	'		'
Beginning balance	'		'	($38.40)	[1]	'
Amounts reclassified from accumulated other comprehensive loss	'		'	9.2	[1]	'
Net current period other comprehensive income	2.9		3.5	9.2	[1]	9.7
Ending balance	-29.2	[1]	'	-29.2	[1]	'
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'		'	'		'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'		'	'		'
Beginning balance	'		'	-35.4	[1]	'
Amounts reclassified from accumulated other comprehensive loss	'		'	8.9	[1]	'
Net current period other comprehensive income	'		'	8.9	[1]	'
Ending balance	-26.5	[1]	'	-26.5	[1]	'
Accumulated Defined Benefit Plans Adjustment [Member]	'		'	'		'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'		'	'		'
Beginning balance	'		'	-3	[1]	'
Amounts reclassified from accumulated other comprehensive loss	'		'	0.3	[1]	'
Net current period other comprehensive income	'		'	0.3	[1]	'
Ending balance	-2.7	[1]	'	-2.7	[1]	'
Kansas City Power and Light Company [Member]	'		'	'		'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'		'	'		'
Beginning balance	'		'	-25.8		'
Net current period other comprehensive income	1.4		1.7	4.2		4.3
Ending balance	-21.6		'	-21.6		'
Kansas City Power and Light Company [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'		'	'		'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'		'	'		'
Beginning balance	'		'	-25.8	[1]	'
Amounts reclassified from accumulated other comprehensive loss	'		'	4.2	[1]	'
Net current period other comprehensive income	'		'	4.2	[1]	'
Ending balance	($21.60)	[1]	'	($21.60)	[1]	'
[1]	Net of tax

Accumulated_Other_Comprehensiv3

Accumulated Other Comprehensive Income (Loss) Reclassification (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Interest charges	($48.90)	($48.10)	($148)	($170.80)
Fuel	-156.6	-164.7	-410	-422.1
Utility operating and maintenance expenses	-170.2	-156.8	-491.8	-484
Income before income tax (expense) benefit and income (loss) from equity investments	225.1	229.1	359.1	300.3
Income tax (expense) benefit	-81.8	-82.6	-126	-104.9
Net income (loss)	143.1	146.4	232.7	195.2
Reclassification out of Accumulated Other Comprehensive Income [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Net income (loss)	-2.9	'	-9.2	'
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Income before income tax (expense) benefit and income (loss) from equity investments	-4.6	'	-14.5	'
Income tax (expense) benefit	1.8	'	5.6	'
Net income (loss)	-2.8	'	-8.9	'
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest Rate Contract [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Interest charges	-4.6	'	-14.3	'
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Commodity Contract [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Fuel	'	'	-0.2	'
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Utility operating and maintenance expenses	-0.1	'	-0.4	'
Income before income tax (expense) benefit and income (loss) from equity investments	-0.1	'	-0.4	'
Income tax (expense) benefit	0	'	0.1	'
Net income (loss)	-0.1	'	-0.3	'
Kansas City Power and Light Company [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Interest charges	-31	-32.4	-94.5	-96.1
Fuel	-111.5	-114.5	-292	-297.8
Utility operating and maintenance expenses	-120.4	-110.5	-345.3	-344.3
Income before income tax (expense) benefit and income (loss) from equity investments	149.5	145.1	235.6	210.8
Income tax (expense) benefit	-53.1	-54.9	-78.8	-74.6
Net income (loss)	96.4	90.2	156.8	136.2
Kansas City Power and Light Company [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Income before income tax (expense) benefit and income (loss) from equity investments	-2.1	'	-6.7	'
Income tax (expense) benefit	0.7	'	2.5	'
Net income (loss)	-1.4	'	-4.2	'
Kansas City Power and Light Company [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest Rate Contract [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Interest charges	-2.1	'	-6.5	'
Kansas City Power and Light Company [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Commodity Contract [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Fuel	'	'	($0.20)	'

Income_Tax_Expense_Details

Income Tax Expense (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Current income taxes	'	'	'	'
Federal	$1	($1.40)	$1	($4.70)
State	-0.4	-0.3	-0.3	0
Current Income Tax Expense (Benefit), Total	0.6	-1.7	0.7	-4.7
Deferred income taxes	'	'	'	'
Federal	67.9	75.1	105.4	97.6
State	13.3	13.9	21.3	18.2
Deferred Income Tax Expense (Benefit), Total	81.2	89	126.7	115.8
Noncurrent income taxes	'	'	'	'
Federal	0	0	0	-0.2
State	0	0	-0.2	0
Foreign	0.1	-4.1	-0.2	-4.2
Noncurrent Income Tax Expense (Benefit), Total	0.1	-4.1	-0.4	-4.4
Investment tax credit	'	'	'	'
Deferral	0.3	0	0.3	0
Amortization	-0.4	-0.6	-1.3	-1.8
Investment Tax Credit, Total	-0.1	-0.6	-1	-1.8
Total income tax expense	81.8	82.6	126	104.9
Effective Income Tax Rate Reconciliation, Percent [Abstract]	'	'	'	'
Federal statutory income tax (in hundredths)	35.00%	35.00%	35.00%	35.00%
Differences between book and tax depreciation not normalized (in hundredths)	-0.50%	0.50%	-0.20%	1.10%
Amortization of investments tax credits (in hundredths)	-0.20%	-0.30%	-0.40%	-0.60%
Federal income tax credits (in hundredths)	-1.60%	-1.00%	-2.80%	-2.80%
State income taxes (in hundredths)	3.70%	3.80%	3.80%	3.90%
Changes in uncertain tax positions, net (in hundredths)	0.10%	-1.80%	-0.10%	-1.40%
Effective Income Tax Rate Reconciliation, Other Adjustments	-0.10%	-0.10%	-0.20%	-0.30%
Effective Income Tax Rate, Continuing Operations, Total	36.40%	36.10%	35.10%	34.90%
Kansas City Power and Light Company [Member]	'	'	'	'
Current income taxes	'	'	'	'
Federal	-0.6	22.9	-1.2	23.1
State	-0.4	4.1	-0.5	4.2
Current Income Tax Expense (Benefit), Total	-1	27	-1.7	27.3
Deferred income taxes	'	'	'	'
Federal	55	22.7	75.6	38.8
State	10.9	4.5	15.9	8.6
Deferred Income Tax Expense (Benefit), Total	65.9	27.2	91.5	47.4
Noncurrent income taxes	'	'	'	'
Federal	-10.1	1	-9	1.1
State	-1.7	0.2	-1.5	0.2
Noncurrent Income Tax Expense (Benefit), Total	-11.8	1.2	-10.5	1.3
Investment tax credit	'	'	'	'
Deferral	0.3	0	0.3	0
Amortization	-0.3	-0.5	-0.8	-1.4
Investment Tax Credit, Total	0	-0.5	-0.5	-1.4
Total income tax expense	$53.10	$54.90	$78.80	$74.60
Effective Income Tax Rate Reconciliation, Percent [Abstract]	'	'	'	'
Federal statutory income tax (in hundredths)	35.00%	35.00%	35.00%	35.00%
Differences between book and tax depreciation not normalized (in hundredths)	-0.90%	0.70%	-0.60%	1.30%
Amortization of investments tax credits (in hundredths)	-0.20%	-0.30%	-0.30%	-0.60%
Federal income tax credits (in hundredths)	-2.20%	-1.50%	-4.20%	-4.00%
State income taxes (in hundredths)	3.80%	3.90%	3.80%	4.00%
Changes in uncertain tax positions, net (in hundredths)	0.10%	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Other Adjustments	-0.10%	0.00%	-0.20%	-0.30%
Effective Income Tax Rate, Continuing Operations, Total	35.50%	37.80%	33.50%	35.40%

Taxes_Uncertain_Tax_Positions_

Taxes Uncertain Tax Positions (Details) (USD $)	9 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Uncertain Tax Positions [Line Items]	'	'
Amount expected to impact the effective tax rate if recognized	$6.80	$7.30
Accrued interest related to unrecognized tax benefits	3.3	3.5
Accrued penalties with respect to unrecognized tax benefits	0.6	0.7
Amount of unrecognized tax benefits that may be recognized in the next twelve months due to statute expirations or settlement agreements with tax authorities	7.2	'
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'	'
Balance at beginning of period	21.4	24
Additions for current year tax positions	0	3.7
Reductions for current year tax positions	-0.3	0
Reductions for prior year tax positions	-10.5	-1.8
Statute expirations	-0.2	-4.7
Foreign currency translation adjustments	-0.2	0.2
Balance at end of period	10.2	21.4
Kansas City Power and Light Company [Member]	'	'
Uncertain Tax Positions [Line Items]	'	'
Amount expected to impact the effective tax rate if recognized	0	0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'	'
Balance at beginning of period	10.5	8.7
Additions for current year tax positions	0	3.6
Reductions for current year tax positions	0	0
Reductions for prior year tax positions	-10.5	-1.6
Statute expirations	0	-0.2
Foreign currency translation adjustments	0	0
Balance at end of period	$0	$10.50

Segments_and_Related_Informati2

Segments and Related Information (Details) (USD $)	3 Months Ended		9 Months Ended			12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]	'	'	'		'	'
Operating revenues	$765	$746.20	$1,907.50		$1,829.50	'
Depreciation and amortization	-73.3	-68.9	-216.1		-204.2	'
Interest charges	-48.9	-48.1	-148		-170.8	'
Income tax (expense) benefit	-81.8	-82.6	-126		-104.9	'
Net income (loss) attributable to Great Plains Energy	143.1	146.2	232.7		195.2	'
Assets, Total	9,869.20	'	9,869.20		'	9,647.30
Capital expenditures	'	'	486.2	[1]	409.5	610.2	[1]
Electric Utility Segment [Member] | Electric Utility Segment [Member]	'	'	'		'	'
Segment Reporting Information [Line Items]	'	'	'		'	'
Operating revenues	765	746.2	1,907.50		1,829.50	'
Depreciation and amortization	-73.3	-68.9	-216.1		-204.2	'
Interest charges	-46.7	-48.4	-141.9		-149.5	'
Income tax (expense) benefit	-83.6	-86.5	-130.1		-120.6	'
Net income (loss) attributable to Great Plains Energy	145.4	141.9	238.5		210.2	'
Assets, Total	10,193.90	'	10,193.90		'	9,910.60
Capital expenditures	'	'	486.2	[1]	'	610.2	[1]
Other [Member]	'	'	'		'	'
Segment Reporting Information [Line Items]	'	'	'		'	'
Operating revenues	0	0	0		0	'
Depreciation and amortization	0	0	0		0	'
Interest charges	-13.6	-12.3	-42.7		-52.5	'
Income tax (expense) benefit	1.8	3.9	4.1		15.7	'
Net income (loss) attributable to Great Plains Energy	-2.3	4.3	-5.8		-15	'
Assets, Total	87.8	'	87.8		'	122.4
Capital expenditures	'	'	0	[1]	'	0	[1]
Eliminations [Member]	'	'	'		'	'
Segment Reporting Information [Line Items]	'	'	'		'	'
Operating revenues	0	0	0		0	'
Depreciation and amortization	0	0	0		0	'
Interest charges	11.4	12.6	36.6		31.2	'
Income tax (expense) benefit	0	0	0		0	'
Net income (loss) attributable to Great Plains Energy	0	0	0		0	'
Assets, Total	-412.5	'	-412.5		'	-385.7
Capital expenditures	'	'	$0	[1]	'	$0	[1]
[1]	Capital expenditures reflect year to date amounts for the periods presented.

Regulatory_Matters_Details

Regulatory Matters (Details) (Missouri Public Service Commission [Member], USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
Kansas City Power and Light Company [Member]	'
Regulatory Proceedings [Line Items]	'
Annual revenue increase authorized	$67.40
KCPL Greater Missouri Operations [Member] | St Joseph Light and Power division [Member]	'
Regulatory Proceedings [Line Items]	'
Annual revenue increase authorized	21.7
KCPL Greater Missouri Operations [Member] | Missouri Public Service division [Member]	'
Regulatory Proceedings [Line Items]	'
Annual revenue increase authorized	$26.20

Regulatory_Matters_Asset_Detai

Regulatory Matters Asset (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Regulatory Assets [Line Items]	'	'
Regulatory Assets, Noncurrent	$1,032.20	$1,120.90
Regulatory Liability, Noncurrent	254.1	283.8
Kansas City Power and Light Company [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory Assets, Noncurrent	799.1	853.2
Regulatory Liability, Noncurrent	$160.70	$153

Regulatory_Matters_Liabilities

Regulatory Matters Liabilities (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities	$254.10	$283.80
Kansas City Power and Light Company [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities	$160.70	$153

Goodwill_and_Intangible_Assets1

Goodwill and Intangible Assets Goodwill (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Goodwill [Line Items]	'	'
Goodwill	$169	$169