Evergy Metro 10-Q 7 Aug 14 2014 Q2 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	6 Months Ended
	Jun. 30, 2014	Aug. 04, 2014
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 Common Stock, Shares Outstanding	'	154,083,123
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q2	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	30-Jun-14	'

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Jun. 30, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Current Assets	'		'
Cash and cash equivalents	$12.50		$10.60
Funds on deposit	1.3		0.8
Receivables, net	219.3		162.2
Accounts receivable pledged as collateral	171		175
Fuel inventories, at average cost	72.5		76.4
Materials and supplies, at average cost	148.2		152.3
Deferred refueling outage costs	21.1		29.5
Refundable income taxes	10.7		10.5
Deferred income taxes	84		80.3
Assets held for sale	0		36.2
Prepaid expenses and other assets	36.1		33.2
Assets, Current, Total	776.7		767
Utility Plant, at Original Cost	'		'
Electric	11,924.20		11,575.30
Less-accumulated depreciation	4,731.70		4,628.40
Net utility plant in service	7,192.50		6,946.90
Construction work in progress	709.7		736.7
Nuclear Fuel, Net of Amortization	68.4		62.8
Public Utilities, Property, Plant and Equipment, Net	7,970.60		7,746.40
Investments and Other Assets	'		'
Nuclear decommissioning trust fund	194.8		183.9
Regulatory Assets	867.6		849.7
Goodwill	169		169
Other Assets, Noncurrent	79.4		79.4
Investments and Other Assets, Total	1,310.80		1,282
Assets, Total	10,058.10		9,795.40
Current Liabilities	'		'
Notes payable	0		9
Collateralized note payable	171		175
Commercial paper	376.5		108.2
Current maturities of long-term debt	15.1		1.1
Accounts payable	277.7		327.4
Accrued taxes	75.7		29.7
Accrued interest	44.1		45.4
Accrued compensation and benefits	38.7		47.3
Pension and post-retirement liability	3.2		3.2
Other Liabilities, Current	25.5		23.5
Liabilities, Current, Total	1,027.50		769.8
Deferred Credits and Other Liabilities	'		'
Deferred income taxes	1,008.20		964.8
Deferred tax credits	126.6		127.4
Asset retirement obligations	163.6		158.8
Pension and post-retirement liability	335.2		360.5
Regulatory Liabilities	282.5		264
Other Liabilities, Noncurrent	98.4		121
Liabilities, Noncurrent, Total	2,014.50		1,996.50
Common shareholders' equity	'		'
Common Stock, Value, Issued	2,635.80		2,631.10
Retained earnings	875.3		871.4
Treasury Stock, Value	-2.3		-2.8
Accumulated other comprehensive loss	-19.8	[1]	-25.3	[1]
Common Shareholders' Equity, Total	3,489		3,474.40
Cumulative preferred stock $100 par value	'		'
Preferred Stock, Value, Issued	39		39
Long-term debt	3,488.10		3,515.70
Total Capitalization	7,016.10		7,029.10
Commitments and Contingencies	'		'
Liabilities and Equity, Total	10,058.10		9,795.40
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	4.7		4
Funds on deposit	0.9		0.7
Receivables, net	161.3		129.2
Accounts Receivable, Related Parties, Current	52.7		50.4
Accounts receivable pledged as collateral	110		110
Fuel inventories, at average cost	43.7		50.3
Materials and supplies, at average cost	106.2		109
Deferred refueling outage costs	21.1		29.5
Refundable income taxes	8.8		15.1
Deferred income taxes	3.5		0
Assets held for sale	0		4.7
Prepaid expenses and other assets	31.5		27.5
Assets, Current, Total	544.4		530.4
Utility Plant, at Original Cost	'		'
Electric	8,578.90		8,274.90
Less-accumulated depreciation	3,587.70		3,518.30
Net utility plant in service	4,991.20		4,756.60
Construction work in progress	618.9		660.4
Nuclear Fuel, Net of Amortization	68.4		62.8
Public Utilities, Property, Plant and Equipment, Net	5,678.50		5,479.80
Investments and Other Assets	'		'
Nuclear decommissioning trust fund	194.8		183.9
Regulatory Assets	591		614.1
Other Assets, Noncurrent	30		31
Investments and Other Assets, Total	815.8		829
Assets, Total	7,038.70		6,839.20
Current Liabilities	'		'
Collateralized note payable	110		110
Commercial paper	288.3		93.2
Current maturities of long-term debt	14		0
Accounts payable	227.4		239.8
Accounts Payable, Related Parties, Current	0		0.2
Accrued taxes	49.3		23.8
Accrued interest	27.6		29.1
Accrued compensation and benefits	38.7		47.3
Pension and post-retirement liability	1.9		1.9
Deferred income taxes	0		1.7
Other Liabilities, Current	13		13
Liabilities, Current, Total	770.2		560
Deferred Credits and Other Liabilities	'		'
Deferred income taxes	946.2		922.1
Deferred tax credits	124.8		125.3
Asset retirement obligations	145.9		141.7
Pension and post-retirement liability	314.8		339.9
Regulatory Liabilities	174		168.3
Other Liabilities, Noncurrent	66.5		90.4
Liabilities, Noncurrent, Total	1,772.20		1,787.70
Common shareholders' equity	'		'
Common Stock, Value, Issued	1,563.10		1,563.10
Retained earnings	652.4		636.4
Accumulated other comprehensive loss	-17.5		-20.2
Common Shareholders' Equity, Total	2,198		2,179.30
Cumulative preferred stock $100 par value	'		'
Long-term debt	2,298.30		2,312.20
Total Capitalization	4,496.30		4,491.50
Commitments and Contingencies	'		'
Liabilities and Equity, Total	$7,038.70		$6,839.20
[1]	Net of tax

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	6 Months Ended	12 Months Ended
In Millions, except Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Utility Plant, at Original Cost	'	'
Nuclear fuel, amortization	$171.70	$161.40
Common shareholder's equity	'	'
Common stock - shares authorized (in shares)	250,000,000	250,000,000
Common stock-shares issued (in shares)	154,163,226	153,995,621
Treasury stock- shares (in shares)	90,194	129,290
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	$171.70	$161.40
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		6 Months Ended
In Millions, except Per Share data, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013
Operating Revenues	'	'	'		'
Electric revenues	$648.40	$600.30	$1,233.50		$1,142.50
Operating Expenses	'	'	'		'
Fuel	115.4	121.2	250.6		253.4
Purchased power	79.1	34.9	124.5		73.7
Transmission	18.7	12.9	36.3		24.3
Utility operating and maintenance expenses	183.4	166.4	364.1		321.6
Depreciation and amortization	75.6	72.6	150.1		142.8
General taxes	50.6	48.1	103.4		95.9
Other General and Administrative Expense	1.4	0.6	2.4		1.1
Costs and Expenses, Total	524.2	456.7	1,031.40		912.8
Operating Income (Loss)	124.2	143.6	202.1		229.7
Non-operating income	7	4.4	13.4		6.9
Non-operating expenses	-3.9	-2.2	-7		-3.5
Interest charges	-48.3	-49.4	-97.7		-99.1
Income before income tax (expense) benefit and income (loss) from equity investments	79	96.4	110.8		134
Income tax (expense) benefit	-27	-32.7	-35.1		-44.2
Income (loss) from equity investments, net of income taxes	0.1	-0.1	0.2		-0.2
Net income (loss)	52.1	63.6	75.9		89.6
Preferred stock dividend requirements	0.4	0.4	0.8		0.8
Earnings (loss) available for common shareholders	51.7	63.2	75.1		88.8
Average number of common shares outstanding (in shares)	153.8	153.5	153.8		153.4
Average number of diluted common shares outstanding (in shares)	154	153.8	154		153.7
Earnings Per Share, Basic and Diluted [Abstract]	'	'	'		'
Earnings Per Share, Basic and Diluted	$0.34	$0.41	$0.49		$0.58
Common Stock, Dividends, Per Share, Declared	$0.23	$0.22	$0.46		$0.44
Other comprehensive income	'	'	'		'
Reclassification to expenses, net of tax	2.5	2.9	5.3		6.1
Derivative hedging activity, net of tax	2.5	2.9	5.3		6.1
Amortization of net losses included in net periodic benefit costs, net of tax	0	0.2	0.2		0.2
Change in unrecognized pension expense, net of tax	0	0.2	0.2		0.2
Total other comprehensive income (loss)	2.5	3.1	5.5	[1]	6.3	[1]
Comprehensive income (loss) attributable to Great Plains Energy	54.6	66.7	81.4		95.9
Kansas City Power and Light Company [Member]	'	'	'		'
Operating Revenues	'	'	'		'
Electric revenues	439.5	410.8	830.5		777.5
Operating Expenses	'	'	'		'
Fuel	88.2	86	181.8		180.5
Purchased power	40.5	18.6	59.4		37.7
Transmission	12	8.8	22.6		16.8
Utility operating and maintenance expenses	129.1	116.7	256.3		224.9
Depreciation and amortization	52.6	49.6	104.3		97.2
General taxes	38.9	37.7	80.4		74.7
Costs and Expenses, Total	361.3	317.4	704.8		631.8
Operating Income (Loss)	78.2	93.4	125.7		145.7
Non-operating income	5.2	3.8	11.2		5.5
Non-operating expenses	-2	-1.2	-3.6		-1.6
Interest charges	-31	-31.5	-61.7		-63.5
Income before income tax (expense) benefit and income (loss) from equity investments	50.4	64.5	71.6		86.1
Income tax (expense) benefit	-15.6	-20.3	-19.6		-25.7
Net income (loss)	34.8	44.2	52		60.4
Other comprehensive income	'	'	'		'
Reclassification to expenses, net of tax	1.4	1.3	2.7		2.8
Derivative hedging activity, net of tax	1.4	1.3	2.7		2.8
Total other comprehensive income (loss)	1.4	1.3	2.7		2.8
Comprehensive income (loss) attributable to Great Plains Energy	$36.20	$45.50	$54.70		$63.20
[1]	Net of tax

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014		Jun. 30, 2013
Cash Flows from Operating Activities	'		'
Net income (loss)	$75.90		$89.60
Adjustments to reconcile income to net cash from operating activities:	'		'
Depreciation and amortization	150.1		142.8
Amortization of:	'		'
Nuclear fuel	10.3		8.7
Other	26.1		28.9
Deferred income taxes, net	38.4		45.5
Investment tax credit amortization	-0.8		-0.9
(Income) loss from equity investments, net of income taxes	-0.2		0.2
Other operating activities	-127.9		-139.4
Net cash from operating activities	171.9		175.4
Cash Flows from Investing Activities	'		'
Utility capital expenditures	-352.9	[1]	-339.8
Allowance for borrowed funds used during construction	-6.9		-4.6
Purchases of nuclear decommissioning trust investments	-13.9		-54.8
Proceeds from nuclear decommissioning trust investments	12.3		53.1
Proceeds from sale of assets	37.7		0
Other investing activities	-17.2		-13.1
Net cash from investing activities	-340.9		-359.2
Cash Flows from Financing Activities	'		'
Issuance of common stock	2.5		2.6
Issuance of long-term debt	0		412.5
Issuance fees	0		-4.3
Repayment of long-term debt	-13.4		-9.3
Net change in short-term borrowings	259.3		-151.1
Net change in collateralized short-term borrowings	-4		1
Dividends paid	-71.6		-67.6
Other financing activities	-1.9		-1.4
Net cash from financing activities	170.9		182.4
Net Change in Cash and Cash Equivalents	1.9		-1.4
Cash and Cash Equivalents at Beginning of Year	10.6		9.3
Cash and Cash Equivalents at End of Period	12.5		7.9
Kansas City Power and Light Company [Member]	'		'
Cash Flows from Operating Activities	'		'
Net income (loss)	52		60.4
Adjustments to reconcile income to net cash from operating activities:	'		'
Depreciation and amortization	104.3		97.2
Amortization of:	'		'
Nuclear fuel	10.3		8.7
Other	15.5		17.1
Deferred income taxes, net	19.2		25.6
Investment tax credit amortization	-0.5		-0.5
Other operating activities	-53.2		-93.2
Net cash from operating activities	147.6		115.3
Cash Flows from Investing Activities	'		'
Utility capital expenditures	-293.4		-261.2
Allowance for borrowed funds used during construction	-6		-4.1
Purchases of nuclear decommissioning trust investments	-13.9		-54.8
Proceeds from nuclear decommissioning trust investments	12.3		53.1
Proceeds from sale of assets	4.7		0
Net money pool lending	0		-36.3
Other investing activities	-9.5		-8.3
Net cash from investing activities	-305.8		-311.6
Cash Flows from Financing Activities	'		'
Issuance of long-term debt	0		412.5
Issuance fees	0		-4.3
Repayment of long-term debt	0		-2.6
Net change in short-term borrowings	195.1		-161
Net money pool borrowings	-0.2		-3.8
Dividends paid	-36		-46
Net cash from financing activities	158.9		194.8
Net Change in Cash and Cash Equivalents	0.7		-1.5
Cash and Cash Equivalents at Beginning of Year	4		5.2
Cash and Cash Equivalents at End of Period	$4.70		$3.70
[1]	Capital expenditures reflect year to date amounts for the periods presented.

Consolidated_Statements_of_Com

Consolidated Statements of Common Shareholders' Equity (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]
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, 2012	'	'	$2,624.70	'	$758.80	$559.40	($5.10)	($38.40)	($25.80)
Beginning balance, treasury stock (in shares) at Dec. 31, 2012	'	'	'	'	'	'	-250,236	'	'
Beginning balance (in shares) at Dec. 31, 2012	'	'	153,779,806	'	'	'	'	'	'
Issuance of common stock	'	'	2.6	'	'	'	'	'	'
Issuance of common stock (in shares)	'	'	114,918	'	'	'	'	'	'
Equity compensation expense, net of forfeitures	'	'	0.2	'	'	'	'	'	'
Unearned Compensation [Abstract]	'	'	'	'	'	'	'	'	'
Issuance of restricted common stock	'	'	-1.7	'	'	'	'	'	'
Compensation expense recognized	'	'	1	'	'	'	'	'	'
Stockholders' Equity, Other	'	'	0.5	'	'	'	'	'	'
Net income (loss)	89.6	60.4	'	'	89.6	60.4	'	'	'
Dividends:	'	'	'	'	'	'	'	'	'
Common stock	'	'	'	'	-66.8	-46	'	'	'
Preferred stock - at required rates	'	'	'	'	-0.8	'	'	'	'
Performance shares	'	'	'	'	-0.2	'	'	'	'
Treasury shares acquired	'	'	'	'	'	'	-1.2	'	'
Treasury shares acquired (in shares)	'	'	'	'	'	'	-55,731	'	'
Treasury shares reissued	'	'	'	'	'	'	3.7	'	'
Treasury shares reissued (in shares)	'	'	'	'	'	'	184,721	'	'
Derivative hedging activity, net of tax	6.1	2.8	'	'	'	'	'	6.1	2.8
Change in unrecognized pension expense, net of tax	0.2	'	'	'	'	'	'	0.2	'
Ending balance at Jun. 30, 2013	3,373.20	2,113.90	2,627.30	1,563.10	780.6	573.8	-2.6	-32.1	-23
Ending balance (in shares) at Jun. 30, 2013	'	'	153,894,724	1	'	'	'	'	'
Ending balance, treasury stock (in shares) at Jun. 30, 2013	'	'	'	'	'	'	-121,246	'	'
Beginning balance at Mar. 31, 2013	'	'	'	'	'	'	'	'	'
Unearned Compensation [Abstract]	'	'	'	'	'	'	'	'	'
Net income (loss)	63.6	44.2	'	'	'	'	'	'	'
Dividends:	'	'	'	'	'	'	'	'	'
Derivative hedging activity, net of tax	2.9	1.3	'	'	'	'	'	'	'
Change in unrecognized pension expense, net of tax	0.2	'	'	'	'	'	'	'	'
Ending balance at Jun. 30, 2013	3,373.20	2,113.90	'	1,563.10	'	'	'	'	'
Ending balance (in shares) at Jun. 30, 2013	'	'	'	1	'	'	'	'	'
Beginning balance at Dec. 31, 2013	3,474.40	2,179.30	2,631.10	'	871.4	636.4	-2.8	-25.3	-20.2
Beginning balance, treasury stock (in shares) at Dec. 31, 2013	-129,290	'	'	'	'	'	-129,290	'	'
Beginning balance (in shares) at Dec. 31, 2013	'	'	153,995,621	'	'	'	'	'	'
Issuance of common stock	'	'	4.3	'	'	'	'	'	'
Issuance of common stock (in shares)	'	'	167,605	'	'	'	'	'	'
Equity compensation expense, net of forfeitures	'	'	0.2	'	'	'	'	'	'
Unearned Compensation [Abstract]	'	'	'	'	'	'	'	'	'
Issuance of restricted common stock	'	'	-1.9	'	'	'	'	'	'
Compensation expense recognized	'	'	1	'	'	'	'	'	'
Stockholders' Equity, Other	'	'	1.1	'	'	'	'	'	'
Net income (loss)	75.9	52	'	'	75.9	52	'	'	'
Dividends:	'	'	'	'	'	'	'	'	'
Common stock	'	'	'	'	-70.8	-36	'	'	'
Preferred stock - at required rates	'	'	'	'	-0.8	'	'	'	'
Performance shares	'	'	'	'	-0.4	'	'	'	'
Treasury shares acquired	'	'	'	'	'	'	-1.9	'	'
Treasury shares acquired (in shares)	'	'	'	'	'	'	-73,273	'	'
Treasury shares reissued	'	'	'	'	'	'	2.4	'	'
Treasury shares reissued (in shares)	'	'	'	'	'	'	112,369	'	'
Derivative hedging activity, net of tax	5.3	2.7	'	'	'	'	'	5.3	2.7
Change in unrecognized pension expense, net of tax	0.2	'	'	'	'	'	'	0.2	'
Ending balance at Jun. 30, 2014	3,489	2,198	2,635.80	1,563.10	875.3	652.4	-2.3	-19.8	-17.5
Ending balance (in shares) at Jun. 30, 2014	'	'	154,163,226	1	'	'	'	'	'
Ending balance, treasury stock (in shares) at Jun. 30, 2014	-90,194	'	'	'	'	'	-90,194	'	'
Beginning balance at Mar. 31, 2014	'	'	'	'	'	'	'	'	'
Unearned Compensation [Abstract]	'	'	'	'	'	'	'	'	'
Net income (loss)	52.1	34.8	'	'	'	'	'	'	'
Dividends:	'	'	'	'	'	'	'	'	'
Derivative hedging activity, net of tax	2.5	1.4	'	'	'	'	'	'	'
Change in unrecognized pension expense, net of tax	0	'	'	'	'	'	'	'	'
Ending balance at Jun. 30, 2014	$3,489	$2,198	'	$1,563.10	'	'	'	'	'
Ending balance (in shares) at Jun. 30, 2014	'	'	'	1	'	'	'	'	'
Ending balance, treasury stock (in shares) at Jun. 30, 2014	-90,194	'	'	'	'	'	'	'	'

Consolidated_Statements_of_Com1

Consolidated Statements of Common Shareholders' Equity (Parenthetical) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Stock Transactions, Parenthetical Disclosures [Abstract]	'	'	'	'
Common Stock, Dividends, Per Share, Declared	$0.23	$0.22	$0.46	$0.44

Summary_of_Significant_Account

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2014
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 significant operations 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 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.
	Great Plains Energy also wholly owns GPE Transmission Holding Company, LLC (GPETHC). GPETHC owns 13.5% of Transource Energy, LLC (Transource) with the remaining 86.5% owned by AEP Transmission Holding Company, LLC (AEPTHC), a subsidiary of American Electric Power Company, Inc. GPETHC accounts for its investment in Transource under the equity method. Transource is focused on the development of competitive electric transmission projects.
	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 18 for additional information.
	Basic and Diluted Earnings per Common Share Calculation
	To determine basic EPS, preferred stock dividend requirements 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 and restricted stock.
	The following table reconciles Great Plains Energy's basic and diluted EPS.
			Three Months Ended						Year to Date
			30-Jun						30-Jun
			2014			2013			2014		2013
	Income		(millions, except per share amounts)
	Net income		$	52.1		$	63.6		$	75.9	$	89.6
	Less: preferred stock dividend requirements		0.4			0.4			0.8		0.8
	Earnings available for common shareholders		$	51.7		$	63.2		$	75.1	$	88.8
	Common Shares Outstanding
	Average number of common shares outstanding		153.8			153.5			153.8		153.4
	Add: effect of dilutive securities		0.2			0.3			0.2		0.3
	Diluted average number of common shares outstanding		154			153.8			154		153.7
	Basic and diluted EPS		$	0.34		$	0.41		$	0.49	$	0.58
	Anti-dilutive shares excluded from the computation of diluted EPS are detailed in the following table.
			Three Months Ended					Year to Date
			30-Jun					30-Jun
			2014		2013			2014		2013
	Performance shares		475,549		55,271			475,549		55,271
	Restricted stock shares		—		—			287		21,652
	Dividends Declared
	In August 2014, 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 September 19, 2014, to shareholders of record as of August 28, 2014.  The Board also declared regular dividends on Great Plains Energy's preferred stock, payable December 1, 2014, to shareholders of record as of November 6, 2014.
	In August 2014, KCP&L’s Board of Directors declared a cash dividend payable to Great Plains Energy of $18 million payable on September 18, 2014.
	New Accounting Standards
	On May 28, 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standard Update (ASU) No. 2014-09, Revenue from Contracts with Customers, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The ASU will replace most existing revenue recognition guidance in Generally Accepted Accounting Principles (GAAP) when it becomes effective. The new standard is effective for the Companies on January 1, 2017. Early application is not permitted. The standard permits the use of either the retrospective or cumulative effect transition method. The Companies are evaluating the effect that ASU No. 2014-09 will have on their consolidated financial statements and related disclosures. The Companies have not yet selected a transition method nor have they determined the effect of the standard on their ongoing financial reporting.

Supplemental_Cash_Flow_Informa

Supplemental Cash Flow Information	6 Months Ended
	Jun. 30, 2014
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 June 30	2014			2013
	Cash flows affected by changes in:	(millions)
	Receivables	$	(57.1	)	$	(25.9	)
	Accounts receivable pledged as collateral	4			(1.0		)
	Fuel inventories	3.9			(7.2		)
	Materials and supplies	4.1			(2.1		)
	Accounts payable	(76.1		)	(116.3		)
	Accrued taxes	46			43.7
	Accrued interest	(1.3		)	(0.2		)
	Deferred refueling outage costs	8.4			(26.4		)
	Pension and post-retirement benefit obligations	5.3			21
	Allowance for equity funds used during construction	(9.0		)	(5.0		)
	Fuel recovery mechanism	(17.3		)	(6.4		)
	Solar rebates paid	(33.3		)	(11.8		)
	Other	(5.5		)	(1.8		)
	Total other operating activities	$	(127.9	)	$	(139.4	)
	Cash paid during the period:
	Interest	$	88.2		$	87.2
	Income taxes	$	0.1		$	0.2
	Non-cash investing activities:
	Liabilities accrued for capital expenditures	$	46.7		$	32.8
	KCP&L Other Operating Activities
	Year to Date June 30	2014			2013
	Cash flows affected by changes in:	(millions)
	Receivables	$	(34.4	)	$	(5.2	)
	Fuel inventories	6.6			(7.5		)
	Materials and supplies	2.8			(1.7		)
	Accounts payable	(38.8		)	(85.8		)
	Accrued taxes	31.9			29.8
	Accrued interest	(1.5		)	0.1
	Deferred refueling outage costs	8.4			(26.4		)
	Pension and post-retirement benefit obligations	4.4			22.3
	Allowance for equity funds used during construction	(8.5		)	(5.0		)
	Fuel recovery mechanism	2.4			(3.1		)
	Solar rebates paid	(10.7		)	(3.0		)
	Other	(15.8		)	(7.7		)
	Total other operating activities	$	(53.2	)	$	(93.2	)
	Cash paid during the period:
	Interest	$	57.2		$	57.4
	Non-cash investing activities:
	Liabilities accrued for capital expenditures	$	39.3		$	29.2

Receivables

Receivables	6 Months Ended
	Jun. 30, 2014
Receivables [Abstract]	'
Receivables [Text Block]	'
	3. RECEIVABLES
	Great Plains Energy's and KCP&L's receivables are detailed in the following table.
		June 30				December 31
			2014				2013
	Great Plains Energy		(millions)
	Customer accounts receivable - billed		$	9.4			$	1.5
	Customer accounts receivable - unbilled		111				74.6
	Allowance for doubtful accounts - customer accounts receivable		(4.5		)		(2.5		)
	Other receivables		103.4				88.6
	Total		$	219.3			$	162.2
	KCP&L
	Customer accounts receivable - billed		$	6.4			$	1.3
	Customer accounts receivable - unbilled		69.5				51.2
	Allowance for doubtful accounts - customer accounts receivable		(2.5		)		(1.1		)
	Other receivables		87.9				77.8
	Total		$	161.3			$	129.2
	Great Plains Energy's and KCP&L's other receivables at June 30, 2014, and December 31, 2013, 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 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 June 30, 2014, and December 31, 2013, Great Plains Energy's accounts receivable pledged as collateral and the corresponding short-term collateralized note payable were $171.0 million and $175.0 million, respectively.  At June 30, 2014, and December 31, 2013, 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. KCP&L and GMO expect to renew these agreements for at least one 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 June 30, 2014	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
						Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(380.9	)		$	380.9			$	—			$	(197.9	)		$	197.9			$	—
	Gain (loss) on sale of accounts receivable (a)		(4.8		)		4.4				(0.4		)		(2.5		)		2.2				(0.7		)
	Servicing fees received (paid)		0.6				(0.6		)		—				0.3				(0.3		)		—
	Fees paid to outside investor		—				(0.3		)		(0.3		)		—				(0.1		)		(0.4		)
	Cash from customers (transferred) received		(348.2		)		348.2				—				(176.5		)		176.5				—
	Cash received from (paid for) receivables purchased		343.8				(343.8		)		—				174.3				(174.3		)		—
	Interest on intercompany note received (paid)		0.1				(0.1		)		—				—				—				—
	Year to Date June 30, 2014	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
						Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(734.0	)		$	734			$	—			$	(391.7	)		$	391.7			$	—
	Gain (loss) on sale of accounts receivable (a)		(9.3		)		9				(0.3		)		(5.0		)		4.7				(0.6		)
	Servicing fees received (paid)		1.2				(1.2		)		—				0.6				(0.6		)		—
	Fees paid to outside investor		—				(0.6		)		(0.6		)		—				(0.3		)		(0.9		)
	Cash from customers (transferred) received		(715.8		)		715.8				—				(377.3		)		377.3				—
	Cash received from (paid for) receivables purchased		706.8				(706.8		)		—				372.6				(372.6		)		—
	Interest on intercompany note received (paid)		0.1				(0.1		)		—				—				—				—
	Three Months Ended June 30, 2013	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
						Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(373.3	)		$	373.3			$	—			$	(202.7	)		$	202.7			$	—
	Gain (loss) on sale of accounts receivable (a)		(4.8		)		4.4				(0.4		)		(2.6		)		2.4				(0.6		)
	Servicing fees received (paid)		0.6				(0.6		)		—				0.3				(0.3		)		—
	Fees paid to outside investor		—				(0.3		)		(0.3		)		—				—				(0.3		)
	Cash from customers (transferred) received		(345.6		)		345.6				—				(184.6		)		184.6				—
	Cash received from (paid for) receivables purchased		341.3				(341.3		)		—				182.3				(182.3		)		—
	Year to Date June 30, 2013	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
						Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(708.0	)		$	708			$	—			$	(388.1	)		$	388.1			$	—
	Gain (loss) on sale of accounts receivable (a)		(9.0		)		8.6				(0.4		)		(4.9		)		4.7				(0.6		)
	Servicing fees received (paid)		1.2				(1.2		)		—				0.6				(0.6		)		—
	Fees paid to outside investor		—				(0.6		)		(0.6		)		—				(0.3		)		(0.9		)
	Cash from customers (transferred) received		(682.3		)		682.3				—				(369.5		)		369.5				—
	Cash received from (paid for) receivables purchased		673.8				(673.8		)		—				364.9				(364.9		)		—
Interest on intercompany note received (paid)		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	6 Months Ended
	Jun. 30, 2014
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.  Wolf Creek paid the DOE a quarterly fee of one-tenth of a cent for each kilowatt hour (kWh) of net nuclear generation delivered and sold for the future disposal of spent nuclear fuel.  KCP&L's 47% share of these costs are charged to fuel expense. The Nuclear Energy Institute, a number of individual utilities, and the National Association of Regulatory Utility Commissioners sued the DOE seeking the suspension of this fee. In January 2014, the DOE submitted a proposal to Congress to set the fee at zero and effective May 16, 2014, this fee is set at zero.
	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. In 2011, the NRC reexamined its decision and ordered the licensing board, consistent with budgetary limitations, to close out its work on the DOE's application.  In August 2013, a federal court of appeals ruled that the NRC must resume its review of the DOE's application.
	Wolf Creek is currently evaluating alternatives for expanding its existing on-site spent nuclear fuel storage to provide additional capacity prior to 2025. Management cannot predict when, or if, an off-site storage site or 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.
		June 30					December 31
		2014					2013
	Decommissioning Trust		(millions)
	Beginning balance January 1		$	183.9				$	154.7
	Contributions		1.6					3.3
	Earned income, net of fees		1.9					2.7
	Net realized gains		0.1					1.7
	Net unrealized gains		7.3					21.5
	Ending balance		$	194.8				$	183.9
	The nuclear decommissioning trust is reported at fair value on the balance sheets and is invested in assets as detailed in the following table.
		June 30, 2014																		December 31, 2013
		Cost			Unrealized Gains						Unrealized					Fair			Cost			Unrealized			Unrealized				Fair
		Basis									Losses					Value			Basis			Gains			Losses				Value
		(millions)
	Equity securities	$	85.3			$	50.1					$	(0.4	)			$	135		$	83.7		$	44.6		$	(0.6	)		$	127.7
	Debt securities	53.1				3.5						(0.1		)			56.5			51			2.5			(0.7		)		52.8
	Other	3.3				—						—					3.3			3.4			—			—				3.4
	Total	$	141.7			$	53.6					$	(0.5	)			$	194.8		$	138.1		$	47.1		$	(1.3	)		$	183.9
	The weighted-average maturity of debt securities held by the trust at June 30, 2014, 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-Jun							30-Jun
		2014			2013				2014				2013
		(millions)
	Realized gains	$	0.5		$	0.4			$	0.7			$	1.9
	Realized losses	(0.5		)	—				(0.6		)		(0.4		)

Regulatory_Matters

Regulatory Matters	6 Months Ended
	Jun. 30, 2014
Regulated Operations [Abstract]	'
Regulatory Matters	'
	5. REGULATORY MATTERS
	KCP&L Kansas Abbreviated Rate Case Proceedings
	In December 2013, KCP&L filed an abbreviated application with The State Corporation Commission of the State of Kansas (KCC) to request an increase to its retail revenues of $12.1 million, which was subsequently updated to $11.5 million, including the recovery of costs to reflect the completion of certain components of environmental upgrades at the La Cygne Station, construction work in progress for those components of the upgrades still under construction and updates to certain regulatory asset amortizations. The previously approved return on equity and rate-making equity ratio for KCP&L were not addressed in this case. In July 2014, KCC issued an order authorizing an increase to retail revenues of $11.5 million effective July 25, 2014.
	KCP&L Kansas La Cygne Rate Case Treatment Request Proceedings
	In July 2014, KCP&L filed a request with KCC to use budget amounts for its Kansas jurisdictional portion of costs for a project to install environmental upgrades at the La Cygne Station in determining its request for new retail rates in its next general rate case. KCP&L also requested to defer to a regulatory asset the Kansas jurisdictional portion of depreciation for the La Cygne project from the time the project is placed into service until the date new retail rates become effective in KCP&L's next general rate case in Kansas. An order is expected later this year.
	The La Cygne project is expected to be in-service by June 2015.
	KCP&L Missouri La Cygne Construction Accounting Request Proceedings
	In June 2014, KCP&L filed a request with the MPSC to use construction accounting for a project to install environmental upgrades at the La Cygne Station. Construction accounting would defer to a regulatory asset KCP&L's Missouri jurisdictional portion of carrying costs (interest) and depreciation expense on the project from the time the project is placed into service until the date new retail rates become effective in KCP&L's next general rate case in Missouri. An order is expected later this year. The La Cygne project is expected to be in-service by June 2015.
	KCP&L Missouri Energy Efficiency Investment Act Proceedings
	In June 2014, the Public Service Commission of the State of Missouri (MPSC) issued an order approving KCP&L's request to recover costs for new and enhanced demand side management programs under the Missouri Energy Efficiency Investment Act (MEEIA). The costs will be recovered through a rider mechanism beginning in August 2014.
	KCP&L and GMO Missouri Transmission Cost Accounting Authority Order Proceeding
	In September 2013, KCP&L and GMO filed an application with the MPSC requesting an accounting authority order to defer transmission costs above or below the amount included in current base rates, including carrying costs, as a regulatory asset or liability with the recovery from or refund to Missouri retail customers to be determined in the next general rate case for each company. In July 2014, the MPSC issued its order denying KCP&L's and GMO's request.
	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 division effective January 26, 2013. In March 2014, the Missouri Court of Appeals, Western District (Court of Appeals) dismissed appeals of the January 9, 2013, MPSC order that were filed in February 2013 by GMO and the Missouri Energy Consumers Group (MECG) regarding various issues.
	GMO Missouri Renewable Energy Standard Rate Adjustment Mechanism Proceedings
	In April 2014, GMO filed an application with the MPSC requesting a Renewable Energy Standard Rate Adjustment Mechanism to recover costs for solar rebates and other compliance costs incurred under the Renewable Energy Standard law in Missouri through a rider mechanism. Annual recovery under the rider would not exceed 1% of GMO's annual revenue requirement as determined by the MPSC in the last rate case.

Pension_Plans_and_Other_Employ

Pension Plans and Other Employee Benefits	6 Months Ended
	Jun. 30, 2014
Compensation and Retirement Disclosure [Abstract]	'
Pension Plans and Other Employee Benefits	'
	6. 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 and GMO, and its 47% ownership share of Wolf Creek Nuclear Operating Corporation (WCNOC) defined benefit plans. For the majority of employees, pension benefits under these plans reflect the employees' compensation, years of service and age at retirement; however, for union employees hired after October 1, 2013, the benefits are derived from a cash balance account formula.  Effective January 1, 2014, the KCP&L non-union plan was closed to future employees. Great Plains Energy also provides certain post-retirement health care and life insurance benefits for substantially all retired employees of KCP&L, GMO and its 47% ownership share of WCNOC.
	KCP&L and GMO record pension and post-retirement expense in accordance with rate orders from the MPSC and KCC that allow the difference between pension and post-retirement costs under 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 June 30	2014			2013			2014			2013
	Components of net periodic benefit costs	(millions)
	Service cost	$	9		$	10.5		$	0.9		$	1.1
	Interest cost	12.7			11.8			2			1.9
	Expected return on plan assets	(12.7		)	(11.8		)	(0.7		)	(0.5		)
	Prior service cost	0.2			0.5			0.8			1.8
	Recognized net actuarial loss	12.4			13.7			—			0.4
	Transition obligation	—			—			0.1			0.1
	Net periodic benefit costs before regulatory adjustment	21.6			24.7			3.1			4.8
	Regulatory adjustment	(0.4		)	(2.8		)	1.1			(0.6		)
	Net periodic benefit costs	$	21.2		$	21.9		$	4.2		$	4.2
		Pension Benefits						Other Benefits
	Year to Date June 30	2014			2013			2014			2013
	Components of net periodic benefit costs	(millions)
	Service cost	$	18.1		$	21		$	1.8		$	2.2
	Interest cost	25.4			23.6			4			3.8
	Expected return on plan assets	(25.4		)	(23.6		)	(1.4		)	(1.0		)
	Prior service cost	0.4			1			1.6			3.6
	Recognized net actuarial loss	24.8			27.4			—			0.9
	Transition obligation	—			—			0.1			0.1
	Net periodic benefit costs before regulatory adjustment	43.3			49.4			6.1			9.6
	Regulatory adjustment	(0.8		)	(6.4		)	2.2			(1.1		)
	Net periodic benefit costs	$	42.5		$	43		$	8.3		$	8.5
	Year to date June 30, 2014, Great Plains Energy contributed $46.1 million to the pension plans and expects to contribute an additional $16.1 million in 2014 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 2014, Great Plains Energy expects to make contributions of $11.3 million to the post-retirement benefit plans, the majority of which is expected to be paid by KCP&L.

Equity_Compensation

Equity Compensation	6 Months Ended
	Jun. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Equity Compensation	'
	7. 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-Jun						30-Jun
			2014		2013			2014		2013
	Great Plains Energy		(millions)
	Equity compensation expense		$	1	$	0.3		$	5.4	$	2.1
	Income tax benefit		0.3		0.1			2		0.7
	KCP&L
	Equity compensation expense		$	0.7	$	0.2		$	3.8	$	1.5
	Income tax benefit		0.3		—			1.4		0.4
	Performance Shares
	Performance share activity year to date June 30, 2014, is summarized in the following table. Performance adjustment represents the number of shares of common stock issued related to performance shares and 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, 2014		430,009			$	23.52
	Granted		214,654			28.78
	Earned		(107,741	)		26.14
	Forfeited		(975	)		24.33
	Performance adjustment		(271	)
	Ending balance June 30, 2014		535,676			25.11
	* weighted-average
	At June 30, 2014, the remaining weighted-average contractual term was 1.7 years. There were no shares granted for the three months ended June 30, 2014, and 2013. The weighted-average grant-date fair value of shares granted was $28.78 and $24.16 year to date June 30, 2014, and 2013, respectively. At June 30, 2014, there was $12.5 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 was $2.8 million and $2.4 million year to date June 30, 2014, and 2013, respectively.
	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 2014, inputs for expected volatility, dividend yield and risk-free rates were 18%, 3.56% and 0.63%, respectively.
	Restricted Stock
	Restricted stock activity year to date June 30, 2014, is summarized in the following table.
		Nonvested			Grant Date
		Restricted Stock			Fair Value*
	Beginning balance January 1, 2014		288,537			$	20.18
	Granted and issued		73,860			25.72
	Vested		(75,789	)		19.27
	Forfeited		(612	)		24.16
	Ending balance June 30, 2014		285,996			21.85
	* weighted-average
	At June 30, 2014, the remaining weighted-average contractual term was 1.5 years. The weighted-average grant-date fair value of shares granted was $25.54 and $25.72 for the three months ended and year to date June 30, 2014, respectively. There were no shares granted for the three months ended June 30, 2013. The weighted-average grant-date fair value of shares granted was $22.45 year to date June 30, 2013.  At June 30, 2014, there was $3.0 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 $0.2 million and $1.5 million for the three months ended and year to date June 30, 2014, respectively. The total fair value of shares vested was insignificant and $0.6 million for the three months ended and year to date June 30, 2013, respectively.

Shortterm_Borrowings_and_Short

Short-term Borrowings and Short-term Bank Lines of Credit	6 Months Ended
	Jun. 30, 2014
Short-term Borrowings and Short-term Bank Lines of Credit [Abstract]	'
Short-term Borrowings and Short-term Bank Lines of Credit [Text Block]	'
	8. SHORT-TERM BORROWINGS AND SHORT-TERM BANK LINES OF CREDIT
	Great Plains Energy's $200 Million Revolving Credit Facility
	Great Plains Energy's $200 million revolving credit facility with a group of banks expires in October 2018.  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 June 30, 2014, Great Plains Energy was in compliance with this covenant.  At June 30, 2014, Great Plains Energy had no outstanding cash borrowings and issued no letters of credit under the credit facility.  At December 31, 2013, Great Plains Energy had $9.0 million of outstanding cash borrowings at a weighted-average interest rate of 1.94% and had issued no letters of credit under the credit facility.
	KCP&L's $600 Million Revolving Credit Facility and Commercial Paper
	KCP&L's $600 million revolving credit facility with a group of banks provides support for its issuance of commercial paper and other general corporate purposes and expires in October 2018.  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 June 30, 2014, KCP&L was in compliance with this covenant.  At June 30, 2014, KCP&L had $288.3 million of commercial paper outstanding at a weighted-average interest rate of 0.29%, had issued letters of credit totaling $2.7 million and had no outstanding cash borrowings under the credit facility.  At December 31, 2013, KCP&L had $93.2 million of commercial paper outstanding at a weighted-average interest rate of 0.29%, had issued letters of credit totaling $3.8 million and had no outstanding cash borrowings under the credit facility.
	GMO's $450 Million Revolving Credit Facility and Commercial Paper
	GMO's $450 million revolving credit facility with a group of banks provides support for its issuance of commercial paper and other general corporate purposes and expires in October 2018. 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 June 30, 2014, GMO was in compliance with this covenant.  At June 30, 2014, GMO had $88.2 million of commercial paper outstanding at a weighted-average interest rate of 0.28%, had issued letters of credit totaling $3.6 million and had no outstanding cash borrowings under the credit facility.  At December 31, 2013, GMO had $15.0 million of commercial paper outstanding at a weighted-average interest rate of 0.66%, had issued letters of credit totaling $16.4 million and had no outstanding cash borrowings under the credit facility.

LongTerm_Debt

Long-Term Debt	6 Months Ended
	Jun. 30, 2014
Debt Disclosure [Abstract]	'
Long-Term Debt	'
	9. LONG-TERM DEBT
	Great Plains Energy's and KCP&L's long-term debt is detailed in the following table.
			June 30				December 31
		Year Due	2014				2013
	KCP&L			(millions)
	General Mortgage Bonds
	2.95% EIRR bonds(a)	2015-2035		$	146.4			$	146.4
	7.15% Series 2009A (8.59% rate)(b)	2019		400				400
	4.65% EIRR Series 2005	2035		50				50
	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				300
	6.05% Series (5.78% rate)(b)	2035		250				250
	5.30% Series	2041		400				400
	EIRR Bonds
	0.06% Series 2007A and 2007B(c)	2035		146.5				146.5
	2.875% Series 2008	2038		23.4				23.4
	Current maturities			(14.0		)		—
	Unamortized discount			(4.0		)		(4.1		)
	Total KCP&L excluding current maturities			2,298.30				2,312.20
	Other Great Plains Energy
	GMO First Mortgage Bonds 9.44% Series	2015-2021		7.9				9
	GMO Pollution Control Bonds
	Wamego Series 1996			—				7.3
	State Environmental 1993			—				5
	GMO Senior Notes
	8.27% Series	2021		80.9				80.9
	3.49% Series A	2025		125				125
	4.06% Series B	2033		75				75
	4.74% Series C	2043		150				150
	GMO Medium Term Notes
	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	2021		350				350
	5.292% Series	2022		287.5				287.5
	Current maturities			(1.1		)		(1.1		)
	Unamortized discount and premium, net			4.6				4.9
	Total Great Plains Energy excluding current maturities			$	3,488.10			$	3,515.70
	(a)	Weighted-average interest rates at June 30, 2014
	(b)	Rate after amortizing gains/losses recognized in OCI on settlements of interest rate hedging instruments
	(c)	Variable rate
	GMO Pollution Control Bonds
	In January 2014, GMO made an early repayment of its $7.3 million Wamego Series 1996 and $5.0 million State Environmental 1993 tax-exempt bonds.

Assets_Held_for_Sale_Assets_He

Assets Held for Sale Assets Held for Sale	6 Months Ended
	Jun. 30, 2014
Assets Held for Sale [Abstract]	'
Assets Held For Sale [Text Block]	'
	10. ASSETS HELD FOR SALE
	At December 31, 2013, Great Plains Energy and KCP&L had $36.2 million and $4.7 million, respectively, of assets held for sale related to the construction of two Southwest Power Pool, Inc. (SPP)-approved regional transmission projects, consisting of an approximately 30-mile, 345kV transmission line from KCP&L's and GMO's Iatan generating station to KCP&L's Nashua substation and the Missouri portion of an approximately 180-mile, 345kV transmission line from Sibley, Missouri to Nebraska City, Nebraska. In December 2013, The Federal Energy Regulatory Commission (FERC) accepted the SPP's approval of the novation of these transmission projects to Transource Missouri, LLC (Transource Missouri), a wholly owned subsidiary of Transource. The sale of the assets, at cost, to Transource Missouri was completed in January 2014, resulting in no gain or loss on the sale. Cash proceeds from the asset sale, including a true-up adjustment for the final value of assets sold, were $37.7 million and $4.7 million for Great Plains Energy and KCP&L, respectively.

Commitments_and_Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	11. 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 total 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 June 30, 2014, had incurred approximately $433 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 regulations or final regulations with implementation plans not yet finalized 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. These other projects 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.  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. In April 2014, the U.S. Supreme Court reversed and remanded the CSAPR back to the D.C. Circuit Court for further proceedings consistent with its opinion. KCP&L and GMO continue to comply with CAIR until resolution of the proceedings on remand at which time the Companies expect that they will be able to comply with the resulting implementation of the CSAPR.
	Best Available Retrofit Technology (BART) 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 (MATS) 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 is installing 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 $230 million.  Westar is also installing less expensive NOx reduction equipment at the other two units and plans 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 18 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 proposed and final rule addressing new units 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.
	In June 2014, the EPA proposed its Clean Power Plan which sets emission guidelines for states to follow in developing plans to address greenhouse gas emissions from existing fossil fuel-fired electric generating units. Specifically, the EPA is proposing state-specific goals based on a rate per ton for CO2 emissions from the power sector, as well as guidelines for states to follow in developing plans to achieve the state-specific goals. Nationwide, by 2030, the EPA states the rule would achieve CO2 emission reductions from the power sector of approximately 30% from CO2 emission levels in 2005.
	The EPA has proposed an interim CO2 goal rate reduction in Kansas and Missouri (average of 2020-2029) of 19% and 17%, respectively, and 2030 targets in Kansas and Missouri of 23% and 21%, respectively. The baseline for these reductions are 2012 CO2 emissions adjusted by EPA in the proposed rule. Each state will have the flexibility to design a program to meet its goal in a manner that reflects its particular circumstances and energy and environmental policy objectives. Each state can do so alone or can collaborate with other states on multi-state plans that may provide additional opportunities for cost savings and flexibility.
	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 energy requirement, through 2034.  KCP&L and GMO project that the acquisition of solar renewable energy credits will be sufficient for compliance with the Missouri solar energy requirements for the foreseeable future.  KCP&L also projects that it will be compliant with the Kansas renewable requirements through 2023.
	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 May 2014, the EPA finalized 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 are subject to the best technology available standards based on studies completed to comply with standards. The rule provides flexibility to work with the states to develop the best technology available to minimize aquatic species impacted by being pinned against intake screens (impingement) or drawn into cooling water systems (entrainment). Although the impact on Great Plains Energy's and KCP&L's operations will not be known until after the studies are completed and reviewed by Kansas and Missouri, 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 September 2015.
	The proposal includes a variety of options to reduce pollutants that are discharged into waterways from 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 are 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. The EPA has committed to take final action regarding the proposed revision of RCRA subtitle D regulations by December 2014.
	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 a disposal site 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 June 30, 2014, and December 31, 2013, 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 June 30, 2014, and December 31, 2013, Great Plains Energy had $1.4 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 $1.3 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	6 Months Ended
	Jun. 30, 2014
Legal Proceedings [Abstract]	'
Legal Proceedings [Text Block]	'
	12. LEGAL PROCEEDINGS
	GMO Western Energy Crisis
	In response to complaints of manipulation of the California energy market, 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 the 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	6 Months Ended
	Jun. 30, 2014
Related Party Transactions [Abstract]	'
Related Party Transactions and Relationships	'
	13. RELATED PARTY TRANSACTIONS AND RELATIONSHIPS
	KCP&L employees manage GMO's business and operate its facilities at cost, including GMO's 18% ownership interest in KCP&L's Iatan Nos. 1 and 2.  The operating expenses and capital costs billed from KCP&L to GMO were $42.6 million and $87.2 million, respectively, for the three months ended and year to date June 30, 2014. These costs totaled $51.7 million and $103.6 million, respectively, for the same periods in 2013.  Additionally, KCP&L and GMO engage in wholesale electricity transactions with each other.  KCP&L's net wholesale sales to GMO were $0.6 million and $11.0 million for the three months ended and year to date June 30, 2014, respectively. KCP&L's net wholesale sales to GMO were $4.6 million and $10.0 million, respectively, for the same periods in 2013.
	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, 2013, KCP&L had a money pool payable to GMO of $0.2 million.  The following table summarizes KCP&L's related party net receivables.
		June 30			December 31
			2014			2013
			(millions)
	Net receivable from GMO		$	33.7		$	32.7
	Net receivable from Great Plains Energy		19			17.5

Derivative_Instruments

Derivative Instruments	6 Months Ended
	Jun. 30, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivative Instruments and Hedging Activities Disclosure [Text Block]	'
	14. 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 wholesale sales, 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 KCP&L Kansas jurisdiction and GMO's utility operations that are recorded to a regulatory asset or liability consistent with KCC and MPSC regulatory orders.
	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 June 30, 2014, 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 arrangements, 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 uses derivative instruments to mitigate exposure to market price fluctuations for wholesale power. 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.
	KCP&L and GMO have Transmission Congestion Rights (TCR) that they utilize to hedge against congestion costs and protect load prices in the SPP Integrated Marketplace, which began operations in March 2014. These financial contracts have been designated as economic hedges (non-hedging derivatives). The fair values of these instruments assigned to KCP&L Missouri jurisdiction are recorded as derivative assets or liabilities with an offsetting entry recorded to electric revenue. The fair values of these instruments assigned to KCP&L Kansas jurisdiction and GMO are recorded as derivative assets or liabilities with an offsetting entry recorded to a regulatory asset or liability. For KCP&L Kansas jurisdiction and GMO, the settlement costs are included in their fuel recovery mechanisms.  A regulatory asset or liability is recorded to reflect the change in the timing of recognition authorized by KCC and MPSC. Recovery of actual costs will not impact earnings, but will impact cash flows due to the timing of the recovery mechanism.
	GMO's risk management policy uses derivative instruments to mitigate price exposure to natural gas price volatility in the market.  At June 30, 2014, GMO had financial contracts in place to hedge approximately 23% and 12% of the expected on-peak natural gas generation and natural gas equivalent purchased power price exposure for the remainder of 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 recovery mechanisms.  A regulatory asset or liability is recorded to reflect the change in the timing of recognition authorized by the MPSC. Recovery of actual costs 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 gross notional contract amount 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.
		June 30								December 31
		2014								2013
		Notional				Fair				Notional				Fair
		Contract				Value				Contract				Value
		Amount								Amount
	Great Plains Energy	(millions)
	Futures contracts
	Non-hedging derivatives	$	22.6			$	0.4			$	19.3			$	(0.6	)
	Forward contracts
	Non-hedging derivatives	46.5				5				47.7				5.2
	Transmission congestion rights
	Non-hedging derivatives	72.5				(0.9		)		22.9				1.7
	Option contracts
	Non-hedging derivatives	1.2				0.1				4.8				1.2
	KCP&L
	Futures contracts
	Non-hedging derivatives	$	13.4			$	0.2			$	7.7			$	(0.2	)
	Transmission congestion rights
	Non-hedging derivatives	58.5				0.9				18				1.1
	Option contracts
	Non-hedging derivatives	1.2				0.1				—				—
	The fair values of Great Plains Energy's and KCP&L's open derivative positions and balance sheet classification are summarized in the following tables.  The fair values below are gross values before netting agreements and netting of cash collateral.
	Great Plains Energy
		Balance Sheet		Asset Derivatives						Liability Derivatives
	June 30, 2014	Classification		Fair Value						Fair Value
	Derivatives Not Designated as Hedging Instruments				(millions)
	Commodity contracts	Other			$	12.9					$	8.3
	December 31, 2013
	Derivatives Not Designated as Hedging Instruments
	Commodity contracts	Other			$	8.5					$	1
	KCP&L
		Balance Sheet		Asset Derivatives						Liability Derivatives
	June 30, 2014	Classification		Fair Value						Fair Value
	Derivatives Not Designated as Hedging Instruments				(millions)
	Commodity contracts	Other			$	6.3					$	5.1
	31-Dec-13
	Derivatives Not Designated as Hedging Instruments
	Commodity contracts	Other			$	1.2					$	0.3
	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-Jun-14	(millions)
	Derivative assets		$	12.9					$	(6.5	)				$	6.4			$	—		$	—		$	6.4
	Derivative liabilities		8.3						(6.5		)				1.8				—			—			1.8
	31-Dec-13
	Derivative assets		$	8.5					$	(0.7	)				$	7.8			$	—		$	—		$	7.8
	Derivative liabilities		1						(0.9		)				0.1				—			—			0.1
	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
	30-Jun-14	(millions)
	Derivative assets		$	6.3					$	(5.1	)				$	1.2			$	—		$	—		$	1.2
Derivative liabilities		5.1						(5.1		)				—				—			—			—
31-Dec-13
Derivative assets		$	1.2					$	(0.1	)				$	1.1			$	—		$	—		$	1.1
Derivative liabilities		0.3						(0.3		)				—				—			—			—
See Note 16 for information regarding amounts reclassified out of accumulated other comprehensive loss for Great Plains Energy and KCP&L.
Great Plains Energy's accumulated OCI at June 30, 2014, includes $9.2 million that is expected to be reclassified to expenses over the next twelve months.  KCP&L's accumulated OCI at June 30, 2014, includes $8.8 million that is expected to be reclassified to expenses over the next twelve months.
The following tables summarize the amounts of gain (loss) recognized for the change in fair value of commodity contract derivatives not designated as hedging instruments for Great Plains Energy and KCP&L.
Great Plains Energy
	Three Months Ended									Year to Date
	30-Jun									30-Jun
Derivatives Not Designated as Hedging Instruments		2014				2013				2014				2013
Location of Gain (Loss)		(millions)
Electric revenues		$	(3.2	)		$	—			$	(2.3	)		$	—
Fuel		0.6				1.4				1				(0.6		)
Purchased power		—				—				0.4				—
Regulatory asset		(4.0		)		(0.7		)		(4.1		)		(1.6		)
Regulatory liability		(0.9		)		—				0.2				—
Total		$	(7.5	)		$	0.7			$	(4.8	)		$	(2.2	)
KCP&L
	Three Months Ended									Year to Date
	30-Jun									30-Jun
Derivatives Not Designated as Hedging Instruments		2014				2013				2014				2013
Location of Gain (Loss)		(millions)
Electric revenues		$	(3.2	)		$	—			$	(2.3	)		$	—
Fuel		0.1				1.6				0.1				0.6
Regulatory asset		(2.1		)		—				(2.2		)		—
Total		$	(5.2	)		$	1.6			$	(4.4	)		$	0.6

Fair_Value_Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2014
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	15. 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 June 30, 2014, the book value and fair value of Great Plains Energy's long-term debt, including current maturities, were $3.5 billion and $3.9 billion, respectively. At December 31, 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 June 30, 2014, the book value and fair value of KCP&L's long-term debt, including current maturities, were $2.3 billion and $2.6 billion, respectively. At December 31, 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.
	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 at June 30, 2014, and December 31, 2013.
	Description	June 30						Netting(e)				Level 1			Level 2				Level 3
		2014
	KCP&L		(millions)
	Assets
	Nuclear decommissioning trust (a)
	Equity securities		$	135					$	—			$	135		$	—			$	—
	Debt securities
	U.S. Treasury		21.3						—				21.3			—				—
	U.S. Agency		4.9						—				—			4.9				—
	State and local obligations		4						—				—			4				—
	Corporate bonds		25.7						—				—			25.7				—
	Foreign governments		0.6						—				—			0.6				—
	Cash equivalents		3.4						—				3.4			—				—
	Other		(0.1		)				—				—			(0.1		)		—
	Total nuclear decommissioning trust		194.8						—				159.7			35.1				—
	Self-insured health plan trust (b)
	Equity securities		1.2						—				1.2			—				—
	Debt securities		8.4						—				—			8.4				—
	Cash and cash equivalents		5.8						—				5.8			—				—
	Total self-insured health plan trust		15.4						—				7			8.4				—
	Derivative instruments (c)		1.2						(5.1		)		0.3			—				6
	Total		211.4						(5.1		)		167			43.5				6
	Liabilities
	Derivative instruments (c)		—						(5.1		)		—			—				5.1
	Total		$	—					$	(5.1	)		$	—		$	—			$	5.1
	Other Great Plains Energy
	Assets
	Derivative instruments (c)		$	5.2					$	(1.4	)		$	0.4		$	3.5			$	2.7
	SERP rabbi trusts (d)
	Equity securities		0.1						—				0.1			—				—
	Fixed income funds		18						—				—			18				—
	Total SERP rabbi trusts		18.1						—				0.1			18				—
	Total		23.3						(1.4		)		0.5			21.5				2.7
	Liabilities
	Derivative instruments (c)		1.8						(1.4		)		0.2			—				3
	Total		$	1.8					$	(1.4	)		$	0.2		$	—			$	3
	Great Plains Energy
	Assets
	Nuclear decommissioning trust (a)		$	194.8					$	—			$	159.7		$	35.1			$	—
	Self-insured health plan trust (b)		15.4						—				7			8.4				—
	Derivative instruments (c)		6.4						(6.5		)		0.7			3.5				8.7
	SERP rabbi trusts (d)		18.1						—				0.1			18				—
	Total		234.7						(6.5		)		167.5			65				8.7
	Liabilities
	Derivative instruments (c)		1.8						(6.5		)		0.2			—				8.1
	Total		$	1.8					$	(6.5	)		$	0.2		$	—			$	8.1
	Description	December 31						Netting(e)				Level 1			Level 2				Level 3
		2013
	KCP&L		(millions)
	Assets
	Nuclear decommissioning trust (a)
	Equity securities		$	127.7					$	—			$	127.7		$	—			$	—
	Debt securities
	U.S. Treasury		21.2						—				21.2			—				—
	U.S. Agency		2.8						—				—			2.8				—
State and local obligations		3.9						—				—			3.9				—
Corporate bonds		24.4						—				—			24.4				—
Foreign governments		0.5						—				—			0.5				—
Cash equivalents		3.8						—				3.8			—				—
Other		(0.4		)				—				—			(0.4		)		—
Total nuclear decommissioning trust		183.9						—				152.7			31.2				—
Self-insured health plan trust (b)
Equity securities		0.9						—				0.9			—				—
Debt securities		9.3						—				0.5			8.8				—
Cash and cash equivalents		3.4						—				3.4			—				—
Other		1.2						—				—			1.2				—
Total self-insured health plan trust		14.8						—				4.8			10				—
Derivative instruments (c)		1.1						(0.1		)		0.1			—				1.1
Total		199.8						(0.1		)		157.6			41.2				1.1
Liabilities
Derivative instruments (c)		—						(0.3		)		0.3			—				—
Total		$	—					$	(0.3	)		$	0.3		$	—			$	—
Other Great Plains Energy
Assets
Derivative instruments (c)		$	6.7					$	(0.6	)		$	0.2		$	4.9			$	2.2
SERP rabbi trusts (d)
Equity securities		0.1						—				0.1			—				—
Fixed income funds		18.6						—				—			18.6				—
Total SERP rabbi trusts		18.7						—				0.1			18.6				—
Total		25.4						(0.6		)		0.3			23.5				2.2
Liabilities
Derivative instruments (c)		0.1						(0.6		)		0.6			0.1				—
Total		$	0.1					$	(0.6	)		$	0.6		$	0.1			$	—
Great Plains Energy
Assets
Nuclear decommissioning trust (a)		$	183.9					$	—			$	152.7		$	31.2			$	—
Self-insured health plan trust (b)		14.8						—				4.8			10				—
Derivative instruments (c)		7.8						(0.7		)		0.3			4.9				3.3
SERP rabbi trusts (d)		18.7						—				0.1			18.6				—
Total		225.2						(0.7		)		157.9			64.7				3.3
Liabilities
Derivative instruments (c)		0.1						(0.9		)		0.9			0.1				—
Total		$	0.1					$	(0.9	)		$	0.9		$	0.1			$	—
(a)	Fair value is based on quoted market prices of the investments held by the fund and/or valuation models.
(b)	Fair value is based on quoted market prices of the investments held by the trust. Debt securities classified as Level 1 are comprised of U.S. Treasury securities. Debt securities classified as Level 2 are comprised of corporate bonds, U.S. Agency, state and local obligations, and other asset-backed securities.
(c)	The fair value of derivative instruments is estimated using market quotes, over-the-counter forward price and volatility curves and correlations among fuel prices, net of estimated credit risk. Derivative instruments classified as Level 1 represent exchange traded derivative instruments. Derivative instruments classified as Level 2 represent non-exchange traded derivative instruments traded in over-the-counter markets. Derivative instruments classified as Level 3 represent non-exchange traded derivatives traded in over-the-counter markets for which observable market data is not available to corroborate the valuation inputs and TCRs valued at the most recent auction price in the SPP Integrated Marketplace.
(d)	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.
(e)	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 December 31, 2013, Great Plains Energy netted $0.2 million 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.
Great Plains Energy
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Derivative Instruments
	2014				2013
	(millions)
Net asset at April 1	$	6.9			$	2.4
Total realized/unrealized gains (losses):
included in electric revenue	(3.2		)		—
included in non-operating income	4				1.9
included in regulatory asset	(4.1		)		—
Purchases	7.3				—
Settlements	(10.3		)		(2.4		)
Net asset at June 30	$	0.6			$	1.9
Total unrealized gains (losses) relating to assets still on the consolidated balance sheet at June 30:
included in electric revenue	$	(2.4	)		$	—
included in non-operating income	$	0.1			$	(0.3	)
included in regulatory asset	$	(4.1	)		$	—
Great Plains Energy
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Derivative Instruments
	2014				2013
	(millions)
Net asset at January 1	$	3.3			$	2.3
Total realized/unrealized gains (losses):
included in electric revenue	(2.3		)		—
included in purchased power expense	0.4				—
included in non-operating income	11.1				4.3
included in regulatory asset	(4.1		)		—
Purchases	13.4				—
Settlements	(21.2		)		(4.7		)
Net asset at June 30	$	0.6			$	1.9
Total unrealized gains (losses) relating to assets still on the consolidated balance sheet at June 30:
included in electric revenue	$	(2.5	)		$	—
included in non-operating income	$	0.2			$	(0.1	)
included in regulatory asset	$	(4.1	)		$	—
KCP&L
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Derivative Instruments
		2014
		(millions)
Net asset at April 1		$	3.9
Total realized/unrealized gains (losses):
included in electric revenue		(3.2		)
included in regulatory asset		(2.1		)
Purchases		6.7
Settlements		(4.4		)
Net asset at June 30		$	0.9
Total unrealized gains (losses) relating to assets still on the consolidated balance sheet at June 30:
included in electric revenue		$	(2.4	)
included in regulatory asset		$	(2.1	)
KCP&L
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Derivative Instruments
		2014
		(millions)
Net asset at January 1		$	1.1
Total realized/unrealized gains (losses):
included in electric revenue		(2.3		)
included in regulatory asset		(2.2		)
Purchases		11.8
Settlements		(7.5		)
Net asset at June 30		$	0.9
Total unrealized gains (losses) relating to assets still on the consolidated balance sheet at June 30:
included in electric revenue		$	(2.5	)
included in regulatory asset		$	(2.2	)

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income (Loss)	6 Months Ended
	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'
Accumulated Other Comprehensive Income (Loss) [Text Block]	'
	16. 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)
	Year to Date June 30, 2014	(millions)
	Beginning balance January 1		$	(23.8	)				$	(1.5	)	$	(25.3	)
	Amounts reclassified from accumulated other comprehensive loss		5.3						0.2			5.5
	Net current period other comprehensive income		5.3						0.2			5.5
	Ending balance June 30		$	(18.5	)				$	(1.3	)	$	(19.8	)
	Year to Date June 30, 2013
	Beginning balance January 1		$	(35.4	)				$	(3.0	)	$	(38.4	)
	Amounts reclassified from accumulated other comprehensive loss		6.1						0.2			6.3
	Net current period other comprehensive income		6.1						0.2			6.3
	Ending balance June 30		$	(29.3	)				$	(2.8	)	$	(32.1	)
	(a) Net of tax
	KCP&L
		Gains and Losses on Cash Flow Hedges(a)
	Year to Date June 30, 2014	(millions)
	Beginning balance January 1		$	(20.2	)
	Amounts reclassified from accumulated other comprehensive loss		2.7
	Net current period other comprehensive income		2.7
	Ending balance June 30		$	(17.5	)
	Year to Date June 30, 2013
	Beginning balance January 1		$	(25.8	)
	Amounts reclassified from accumulated other comprehensive loss		2.8
	Net current period other comprehensive income		2.8
	Ending balance June 30		$	(23.0	)
	(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 June 30	2014				2013
		(millions)
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts	$	(3.9	)		$	(4.7	)		Interest charges
		(3.9		)		(4.7		)		Income before income tax expense and income (loss) from equity investments
		1.4				1.8				Income tax benefit
		$	(2.5	)		$	(2.9	)		Net income
	Amortization of defined benefit pension items
	Net losses included in net periodic benefit costs	(0.1		)		(0.3		)		Utility operating and maintenance expenses
		(0.1		)		(0.3		)		Income before income tax expense and income (loss) from equity investments
		0.1				0.1				Income tax benefit
		—				(0.2		)		Net income
	Total reclassifications, net of tax	$	(2.5	)		$	(3.1	)		Net income
	Year to Date June 30	2014				2013
		(millions)
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts	$	(8.6	)		$	(9.7	)		Interest charges
	Commodity contracts	—				(0.2		)		Fuel
		(8.6		)		(9.9		)		Income before income tax expense and income (loss) from equity investments
		3.3				3.8				Income tax benefit
		$	(5.3	)		$	(6.1	)		Net income
	Amortization of defined benefit pension items
	Net losses included in net periodic benefit costs	(0.3		)		(0.3		)		Utility operating and maintenance expenses
		(0.3		)		(0.3		)		Income before income tax expense and income (loss) from equity investments
		0.1				0.1				Income tax benefit
		(0.2		)		(0.2		)		Net income
	Total reclassifications, net of tax	$	(5.5	)		$	(6.3	)		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 June 30	2014				2013
		(millions)
	Gains and (losses) on cash flow hedges (effective portion)
Interest rate contracts	$	(2.2	)		$	(2.2	)		Interest charges
	(2.2		)		(2.2		)		Income before income tax expense
	0.8				0.9				Income tax benefit
Total reclassifications, net of tax	$	(1.4	)		$	(1.3	)		Net income
Year to Date June 30	2014				2013
	(millions)
Gains and (losses) on cash flow hedges (effective portion)
Interest rate contracts	$	(4.4	)		$	(4.4	)		Interest charges
Commodity contracts	—				(0.2		)		Fuel
	(4.4		)		(4.6		)		Income before income tax expense
	1.7				1.8				Income tax benefit
Total reclassifications, net of tax	$	(2.7	)		$	(2.8	)		Net income

Taxes

Taxes	6 Months Ended
	Jun. 30, 2014
Income Tax Disclosure [Abstract]	'
Income Tax Disclosure [Text Block]	'
	17. TAXES
	Components of income tax expense are detailed in the following tables.
		Three Months Ended								Year to Date
		30-Jun								30-Jun
	Great Plains Energy	2014				2013				2014			2013
	Current income taxes	(millions)
	Federal	$	(0.2	)		$	—			$	0.1		$	—
	State	—				0.2				0.1			0.1
	Total	(0.2		)		0.2				0.2			0.1
	Deferred income taxes
	Federal	25				27.6				31.6			37.5
	State	5.1				5.7				6.8			8
	Total	30.1				33.3				38.4			45.5
	Noncurrent income taxes
	Federal	(2.4		)		—				(2.4		)	—
	State	(0.3		)		(0.2		)		(0.3		)	(0.2		)
	Foreign	0.2				(0.2		)		—			(0.3		)
	Total	(2.5		)		(0.4		)		(2.7		)	(0.5		)
	Investment tax credit amortization	(0.4		)		(0.4		)		(0.8		)	(0.9		)
	Income tax expense	$	27			$	32.7			$	35.1		$	44.2
		Three Months Ended								Year to Date
		30-Jun								30-Jun
	KCP&L	2014				2013				2014			2013
	Current income taxes	(millions)
	Federal	$	(2.0	)		$	(0.3	)		$	0.7		$	(0.6	)
	State	(0.3		)		(0.1		)		0.2			(0.1		)
	Total	(2.3		)		(0.4		)		0.9			(0.7		)
	Deferred income taxes
	Federal	14.9				16.6				15.3			20.6
	State	3.3				3.7				3.9			5
	Total	18.2				20.3				19.2			25.6
	Noncurrent income taxes
	Federal	—				0.6				—			1.1
	State	—				0.1				—			0.2
	Total	—				0.7				—			1.3
	Investment tax credit amortization	(0.3		)		(0.3		)		(0.5		)	(0.5		)
	Income tax expense	$	15.6			$	20.3			$	19.6		$	25.7
	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-Jun						30-Jun
	Great Plains Energy	2014			2013			2014			2013
	Federal statutory income tax rate	35	%		35	%		35	%		35	%
	Differences between book and tax depreciation not normalized	(0.6	)		(0.3	)		(0.9	)		0.2
	Amortization of investment tax credits	(0.5	)		(0.4	)		(0.7	)		(0.6	)
	Federal income tax credits	(3.8	)		(3.8	)		(5.4	)		(5.0	)
	State income taxes	3.8			3.8			3.8			3.9
	Changes in uncertain tax positions, net	0.3			(0.3	)		—			(0.4	)
	Other	(0.2	)		(0.1	)		(0.3	)		(0.1	)
	Effective income tax rate	34	%		33.9	%		31.5	%		33	%
		Three Months Ended						Year to Date
		30-Jun						30-Jun
	KCP&L	2014			2013			2014			2013
	Federal statutory income tax rate	35	%		35	%		35	%		35	%
	Differences between book and tax depreciation not normalized	(0.9	)		(0.7	)		(1.8	)		(0.1	)
	Amortization of investment tax credits	(0.5	)		(0.4	)		(0.7	)		(0.6	)
	Federal income tax credits	(5.9	)		(5.7	)		(8.3	)		(7.7	)
	State income taxes	3.8			3.8			3.7			3.8
	Changes in uncertain tax positions, net	—			(0.1	)		—			(0.1	)
	Other	(0.5	)		(0.3	)		(0.6	)		(0.4	)
	Effective income tax rate	31	%		31.6	%		27.3	%		29.9	%
	Uncertain Tax Positions
	At June 30, 2014, and December 31, 2013, Great Plains Energy had $8.9 million and $9.8 million, respectively, of liabilities related to unrecognized tax benefits. Of these amounts, $6.5 million at June 30, 2014, and December 31, 2013 are expected to impact the effective tax rate if recognized.
The following table reflects activity for Great Plains Energy related to the liability for unrecognized tax benefits.
	30-Jun						31-Dec
	2014						2013
	(millions)
Beginning balance January 1		$	9.8					$	21.4
Reductions for current year tax positions		(0.2		)				(0.3		)
Reductions for prior year tax positions		(0.7		)				(10.5		)
Statute expirations		—						(0.3		)
Foreign currency translation adjustments		—						(0.5		)
Ending balance		$	8.9					$	9.8
Great Plains Energy recognizes interest related to unrecognized tax benefits in interest expense and penalties in non-operating expenses.  At June 30, 2014, and December 31, 2013, amounts accrued for interest related to unrecognized tax benefits for Great Plains Energy were $3.4 million and $3.2 million, respectively. Amounts accrued for penalties with respect to unrecognized tax benefits for Great Plains Energy were $0.6 million at June 30, 2014, and December 31, 2013.
In the third quarter of 2014, Great Plains energy will recognize $6.1 million of unrecognized tax benefits, which are related to the former GMO non-regulated operations, and is expected to impact the effective tax rate.

Segments_and_Related_Informati

Segments and Related Information	6 Months Ended
	Jun. 30, 2014
Segment Reporting [Abstract]	'
Segments and Related Information	'
	18. 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, GPETHC and unallocated corporate charges.  The summary of significant accounting policies applies to the reportable segment.  Segment performance is evaluated based on net income.
	The following tables reflect summarized financial information concerning Great Plains Energy's reportable segment.
	Three Months Ended	Electric				Other				Eliminations				Great Plains
	30-Jun-14	Utility												Energy
		(millions)
	Operating revenues		$	648.4			$	—			$	—			$	648.4
	Depreciation and amortization		(75.6		)		—				—				(75.6		)
	Interest (charges) income		(46.0		)		(11.7		)		9.4				(48.3		)
	Income tax (expense) benefit		(28.0		)		1				—				(27.0		)
	Net income (loss)		54.7				(2.6		)		—				52.1
	Year to Date	Electric				Other				Eliminations				Great Plains
	30-Jun-14	Utility												Energy
		(millions)
	Operating revenues		$	1,233.50			$	—			$	—			$	1,233.50
	Depreciation and amortization		(150.1		)		—				—				(150.1		)
	Interest (charges) income		(93.0		)		(24.3		)		19.6				(97.7		)
	Income tax (expense) benefit		(37.8		)		2.7				—				(35.1		)
	Net income (loss)		80.8				(4.9		)		—				75.9
	Three Months Ended	Electric				Other				Eliminations				Great Plains
	30-Jun-13	Utility												Energy
		(millions)
	Operating revenues		$	600.3			$	—			$	—			$	600.3
	Depreciation and amortization		(72.6		)		—				—				(72.6		)
	Interest (charges) income		(47.4		)		(14.6		)		12.6				(49.4		)
	Income tax (expense) benefit		(33.9		)		1.2				—				(32.7		)
	Net income (loss)		65.5				(1.9		)		—				63.6
	Year to Date	Electric				Other				Eliminations				Great Plains
	30-Jun-13	Utility												Energy
		(millions)
	Operating revenues		$	1,142.50			$	—			$	—			$	1,142.50
	Depreciation and amortization		(142.8		)		—				—				(142.8		)
	Interest (charges) income		(95.2		)		(29.1		)		25.2				(99.1		)
	Income tax (expense) benefit		(46.5		)		2.3				—				(44.2		)
	Net income (loss)		93.1				(3.5		)		—				89.6
		Electric				Other				Eliminations				Great Plains
		Utility												Energy
	June 30, 2014		(millions)
	Assets		$	10,325.70			$	120.8			$	(388.4	)		$	10,058.10
	Capital expenditures(a)		352.9				—				—				352.9
	December 31, 2013
	Assets		$	10,019.60			$	105.6			$	(329.8	)		$	9,795.40
	Capital expenditures(a)		669				—				—				669
	(a) Capital expenditures reflect year to date amounts for the periods presented.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2014
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 significant operations 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 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.
	Great Plains Energy also wholly owns GPE Transmission Holding Company, LLC (GPETHC). GPETHC owns 13.5% of Transource Energy, LLC (Transource) with the remaining 86.5% owned by AEP Transmission Holding Company, LLC (AEPTHC), a subsidiary of American Electric Power Company, Inc. GPETHC accounts for its investment in Transource under the equity method. Transource is focused on the development of competitive electric transmission projects.
	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 18 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 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 and restricted stock.
	The following table reconciles Great Plains Energy's basic and diluted EPS.
			Three Months Ended						Year to Date
			30-Jun						30-Jun
			2014			2013			2014		2013
	Income		(millions, except per share amounts)
	Net income		$	52.1		$	63.6		$	75.9	$	89.6
	Less: preferred stock dividend requirements		0.4			0.4			0.8		0.8
	Earnings available for common shareholders		$	51.7		$	63.2		$	75.1	$	88.8
	Common Shares Outstanding
	Average number of common shares outstanding		153.8			153.5			153.8		153.4
	Add: effect of dilutive securities		0.2			0.3			0.2		0.3
	Diluted average number of common shares outstanding		154			153.8			154		153.7
	Basic and diluted EPS		$	0.34		$	0.41		$	0.49	$	0.58
	Anti-dilutive shares excluded from the computation of diluted EPS are detailed in the following table.
			Three Months Ended					Year to Date
			30-Jun					30-Jun
			2014		2013			2014		2013
	Performance shares		475,549		55,271			475,549		55,271
	Restricted stock shares		—		—			287		21,652
New Accounting Pronouncements, Policy [Policy Text Block]	'
	New Accounting Standards
	On May 28, 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standard Update (ASU) No. 2014-09, Revenue from Contracts with Customers, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The ASU will replace most existing revenue recognition guidance in Generally Accepted Accounting Principles (GAAP) when it becomes effective. The new standard is effective for the Companies on January 1, 2017. Early application is not permitted. The standard permits the use of either the retrospective or cumulative effect transition method. The Companies are evaluating the effect that ASU No. 2014-09 will have on their consolidated financial statements and related disclosures. The Companies have not yet selected a transition method nor have they determined the effect of the standard on their ongoing financial reporting.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2014
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-Jun						30-Jun
		2014			2013			2014		2013
	Income	(millions, except per share amounts)
	Net income	$	52.1		$	63.6		$	75.9	$	89.6
	Less: preferred stock dividend requirements	0.4			0.4			0.8		0.8
	Earnings available for common shareholders	$	51.7		$	63.2		$	75.1	$	88.8
	Common Shares Outstanding
	Average number of common shares outstanding	153.8			153.5			153.8		153.4
	Add: effect of dilutive securities	0.2			0.3			0.2		0.3
	Diluted average number of common shares outstanding	154			153.8			154		153.7
	Basic and diluted EPS	$	0.34		$	0.41		$	0.49	$	0.58
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-Jun					30-Jun
		2014		2013			2014		2013
	Performance shares	475,549		55,271			475,549		55,271
	Restricted stock shares	—		—			287		21,652

Supplemental_Cash_Flow_Informa1

Supplemental Cash Flow Information (Tables)	6 Months Ended
	Jun. 30, 2014
Supplemental Cash Flow Elements [Abstract]	'
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	'
	Great Plains Energy Other Operating Activities
	Year to Date June 30	2014			2013
	Cash flows affected by changes in:	(millions)
	Receivables	$	(57.1	)	$	(25.9	)
	Accounts receivable pledged as collateral	4			(1.0		)
	Fuel inventories	3.9			(7.2		)
	Materials and supplies	4.1			(2.1		)
	Accounts payable	(76.1		)	(116.3		)
	Accrued taxes	46			43.7
	Accrued interest	(1.3		)	(0.2		)
	Deferred refueling outage costs	8.4			(26.4		)
	Pension and post-retirement benefit obligations	5.3			21
	Allowance for equity funds used during construction	(9.0		)	(5.0		)
	Fuel recovery mechanism	(17.3		)	(6.4		)
	Solar rebates paid	(33.3		)	(11.8		)
	Other	(5.5		)	(1.8		)
	Total other operating activities	$	(127.9	)	$	(139.4	)
	Cash paid during the period:
	Interest	$	88.2		$	87.2
	Income taxes	$	0.1		$	0.2
	Non-cash investing activities:
	Liabilities accrued for capital expenditures	$	46.7		$	32.8
	KCP&L Other Operating Activities
	Year to Date June 30	2014			2013
	Cash flows affected by changes in:	(millions)
	Receivables	$	(34.4	)	$	(5.2	)
	Fuel inventories	6.6			(7.5		)
	Materials and supplies	2.8			(1.7		)
	Accounts payable	(38.8		)	(85.8		)
	Accrued taxes	31.9			29.8
	Accrued interest	(1.5		)	0.1
	Deferred refueling outage costs	8.4			(26.4		)
	Pension and post-retirement benefit obligations	4.4			22.3
	Allowance for equity funds used during construction	(8.5		)	(5.0		)
	Fuel recovery mechanism	2.4			(3.1		)
	Solar rebates paid	(10.7		)	(3.0		)
	Other	(15.8		)	(7.7		)
	Total other operating activities	$	(53.2	)	$	(93.2	)
	Cash paid during the period:
	Interest	$	57.2		$	57.4
	Non-cash investing activities:
	Liabilities accrued for capital expenditures	$	39.3		$	29.2

Receivables_Tables

Receivables (Tables)	6 Months Ended
	Jun. 30, 2014
Receivables [Abstract]	'
Schedule of receivables [Table Text Block]	'
	Great Plains Energy's and KCP&L's receivables are detailed in the following table.
		June 30				December 31
			2014				2013
	Great Plains Energy		(millions)
	Customer accounts receivable - billed		$	9.4			$	1.5
	Customer accounts receivable - unbilled		111				74.6
	Allowance for doubtful accounts - customer accounts receivable		(4.5		)		(2.5		)
	Other receivables		103.4				88.6
	Total		$	219.3			$	162.2
	KCP&L
	Customer accounts receivable - billed		$	6.4			$	1.3
	Customer accounts receivable - unbilled		69.5				51.2
	Allowance for doubtful accounts - customer accounts receivable		(2.5		)		(1.1		)
	Other receivables		87.9				77.8
	Total		$	161.3			$	129.2
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 June 30, 2014	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
						Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(380.9	)		$	380.9			$	—			$	(197.9	)		$	197.9			$	—
	Gain (loss) on sale of accounts receivable (a)		(4.8		)		4.4				(0.4		)		(2.5		)		2.2				(0.7		)
	Servicing fees received (paid)		0.6				(0.6		)		—				0.3				(0.3		)		—
	Fees paid to outside investor		—				(0.3		)		(0.3		)		—				(0.1		)		(0.4		)
	Cash from customers (transferred) received		(348.2		)		348.2				—				(176.5		)		176.5				—
	Cash received from (paid for) receivables purchased		343.8				(343.8		)		—				174.3				(174.3		)		—
	Interest on intercompany note received (paid)		0.1				(0.1		)		—				—				—				—
	Year to Date June 30, 2014	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
						Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(734.0	)		$	734			$	—			$	(391.7	)		$	391.7			$	—
	Gain (loss) on sale of accounts receivable (a)		(9.3		)		9				(0.3		)		(5.0		)		4.7				(0.6		)
	Servicing fees received (paid)		1.2				(1.2		)		—				0.6				(0.6		)		—
	Fees paid to outside investor		—				(0.6		)		(0.6		)		—				(0.3		)		(0.9		)
	Cash from customers (transferred) received		(715.8		)		715.8				—				(377.3		)		377.3				—
	Cash received from (paid for) receivables purchased		706.8				(706.8		)		—				372.6				(372.6		)		—
	Interest on intercompany note received (paid)		0.1				(0.1		)		—				—				—				—
	Three Months Ended June 30, 2013	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
						Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(373.3	)		$	373.3			$	—			$	(202.7	)		$	202.7			$	—
	Gain (loss) on sale of accounts receivable (a)		(4.8		)		4.4				(0.4		)		(2.6		)		2.4				(0.6		)
	Servicing fees received (paid)		0.6				(0.6		)		—				0.3				(0.3		)		—
	Fees paid to outside investor		—				(0.3		)		(0.3		)		—				—				(0.3		)
	Cash from customers (transferred) received		(345.6		)		345.6				—				(184.6		)		184.6				—
	Cash received from (paid for) receivables purchased		341.3				(341.3		)		—				182.3				(182.3		)		—
	Year to Date June 30, 2013	KCP&L				KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
						Receivables				KCP&L								Receivables
						Company												Company
		(millions)
	Receivables (sold) purchased		$	(708.0	)		$	708			$	—			$	(388.1	)		$	388.1			$	—
	Gain (loss) on sale of accounts receivable (a)		(9.0		)		8.6				(0.4		)		(4.9		)		4.7				(0.6		)
	Servicing fees received (paid)		1.2				(1.2		)		—				0.6				(0.6		)		—
	Fees paid to outside investor		—				(0.6		)		(0.6		)		—				(0.3		)		(0.9		)
	Cash from customers (transferred) received		(682.3		)		682.3				—				(369.5		)		369.5				—
	Cash received from (paid for) receivables purchased		673.8				(673.8		)		—				364.9				(364.9		)		—
	Interest on intercompany note received (paid)		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)	6 Months Ended
	Jun. 30, 2014
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.
		June 30					December 31
		2014					2013
	Decommissioning Trust		(millions)
	Beginning balance January 1		$	183.9				$	154.7
	Contributions		1.6					3.3
	Earned income, net of fees		1.9					2.7
	Net realized gains		0.1					1.7
	Net unrealized gains		7.3					21.5
	Ending balance		$	194.8				$	183.9
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.
		June 30, 2014																		December 31, 2013
		Cost			Unrealized Gains						Unrealized					Fair			Cost			Unrealized			Unrealized				Fair
		Basis									Losses					Value			Basis			Gains			Losses				Value
		(millions)
	Equity securities	$	85.3			$	50.1					$	(0.4	)			$	135		$	83.7		$	44.6		$	(0.6	)		$	127.7
	Debt securities	53.1				3.5						(0.1		)			56.5			51			2.5			(0.7		)		52.8
	Other	3.3				—						—					3.3			3.4			—			—				3.4
	Total	$	141.7			$	53.6					$	(0.5	)			$	194.8		$	138.1		$	47.1		$	(1.3	)		$	183.9
Gains and losses from the sale of securities by the nuclear decommissioning trust fund	'
		Three Months Ended							Year to Date
		30-Jun							30-Jun
		2014			2013				2014				2013
		(millions)
	Realized gains	$	0.5		$	0.4			$	0.7			$	1.9
	Realized losses	(0.5		)	—				(0.6		)		(0.4		)

Pension_Plans_and_Other_Employ1

Pension Plans and Other Employee Benefits (Tables)	6 Months Ended
	Jun. 30, 2014
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 June 30	2014			2013			2014			2013
	Components of net periodic benefit costs	(millions)
	Service cost	$	9		$	10.5		$	0.9		$	1.1
	Interest cost	12.7			11.8			2			1.9
	Expected return on plan assets	(12.7		)	(11.8		)	(0.7		)	(0.5		)
	Prior service cost	0.2			0.5			0.8			1.8
	Recognized net actuarial loss	12.4			13.7			—			0.4
	Transition obligation	—			—			0.1			0.1
	Net periodic benefit costs before regulatory adjustment	21.6			24.7			3.1			4.8
	Regulatory adjustment	(0.4		)	(2.8		)	1.1			(0.6		)
	Net periodic benefit costs	$	21.2		$	21.9		$	4.2		$	4.2
		Pension Benefits						Other Benefits
	Year to Date June 30	2014			2013			2014			2013
	Components of net periodic benefit costs	(millions)
	Service cost	$	18.1		$	21		$	1.8		$	2.2
	Interest cost	25.4			23.6			4			3.8
	Expected return on plan assets	(25.4		)	(23.6		)	(1.4		)	(1.0		)
	Prior service cost	0.4			1			1.6			3.6
	Recognized net actuarial loss	24.8			27.4			—			0.9
	Transition obligation	—			—			0.1			0.1
	Net periodic benefit costs before regulatory adjustment	43.3			49.4			6.1			9.6
	Regulatory adjustment	(0.8		)	(6.4		)	2.2			(1.1		)
	Net periodic benefit costs	$	42.5		$	43		$	8.3		$	8.5

Equity_Compensation_Tables

Equity Compensation (Tables)	6 Months Ended
	Jun. 30, 2014
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-Jun						30-Jun
			2014		2013			2014		2013
	Great Plains Energy		(millions)
	Equity compensation expense		$	1	$	0.3		$	5.4	$	2.1
	Income tax benefit		0.3		0.1			2		0.7
	KCP&L
	Equity compensation expense		$	0.7	$	0.2		$	3.8	$	1.5
	Income tax benefit		0.3		—			1.4		0.4
Performance share activity	'
		Performance			Grant Date
		Shares			Fair Value*
	Beginning balance January 1, 2014		430,009			$	23.52
	Granted		214,654			28.78
	Earned		(107,741	)		26.14
	Forfeited		(975	)		24.33
	Performance adjustment		(271	)
	Ending balance June 30, 2014		535,676			25.11
	* weighted-average
Restricted stock activity	'
		Nonvested			Grant Date
		Restricted Stock			Fair Value*
	Beginning balance January 1, 2014		288,537			$	20.18
	Granted and issued		73,860			25.72
	Vested		(75,789	)		19.27
	Forfeited		(612	)		24.16
	Ending balance June 30, 2014		285,996			21.85
	* weighted-average

LongTerm_Debt_Tables

Long-Term Debt (Tables)	6 Months Ended
	Jun. 30, 2014
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.
			June 30				December 31
		Year Due	2014				2013
	KCP&L			(millions)
	General Mortgage Bonds
	2.95% EIRR bonds(a)	2015-2035		$	146.4			$	146.4
	7.15% Series 2009A (8.59% rate)(b)	2019		400				400
	4.65% EIRR Series 2005	2035		50				50
	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				300
	6.05% Series (5.78% rate)(b)	2035		250				250
	5.30% Series	2041		400				400
	EIRR Bonds
	0.06% Series 2007A and 2007B(c)	2035		146.5				146.5
	2.875% Series 2008	2038		23.4				23.4
	Current maturities			(14.0		)		—
	Unamortized discount			(4.0		)		(4.1		)
	Total KCP&L excluding current maturities			2,298.30				2,312.20
	Other Great Plains Energy
	GMO First Mortgage Bonds 9.44% Series	2015-2021		7.9				9
	GMO Pollution Control Bonds
	Wamego Series 1996			—				7.3
	State Environmental 1993			—				5
	GMO Senior Notes
	8.27% Series	2021		80.9				80.9
	3.49% Series A	2025		125				125
	4.06% Series B	2033		75				75
	4.74% Series C	2043		150				150
	GMO Medium Term Notes
	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	2021		350				350
	5.292% Series	2022		287.5				287.5
	Current maturities			(1.1		)		(1.1		)
	Unamortized discount and premium, net			4.6				4.9
	Total Great Plains Energy excluding current maturities			$	3,488.10			$	3,515.70
	(a)	Weighted-average interest rates at June 30, 2014
	(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)	6 Months Ended
	Jun. 30, 2014
Related Party Transactions [Abstract]	'
Schedule of related party receivables and payables [Table Text Block]	'
	The following table summarizes KCP&L's related party net receivables.
		June 30			December 31
			2014			2013
			(millions)
	Net receivable from GMO		$	33.7		$	32.7
	Net receivable from Great Plains Energy		19			17.5

Derivative_Instruments_Tables

Derivative Instruments (Tables)	6 Months Ended
	Jun. 30, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Values of open positions for derivative instruments [Table Text Block]	'
	The gross notional contract amount 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.
		June 30								December 31
		2014								2013
		Notional				Fair				Notional				Fair
		Contract				Value				Contract				Value
		Amount								Amount
	Great Plains Energy	(millions)
	Futures contracts
	Non-hedging derivatives	$	22.6			$	0.4			$	19.3			$	(0.6	)
	Forward contracts
	Non-hedging derivatives	46.5				5				47.7				5.2
	Transmission congestion rights
	Non-hedging derivatives	72.5				(0.9		)		22.9				1.7
	Option contracts
	Non-hedging derivatives	1.2				0.1				4.8				1.2
	KCP&L
	Futures contracts
	Non-hedging derivatives	$	13.4			$	0.2			$	7.7			$	(0.2	)
	Transmission congestion rights
	Non-hedging derivatives	58.5				0.9				18				1.1
	Option contracts
	Non-hedging derivatives	1.2				0.1				—				—
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 and balance sheet classification are summarized in the following tables.  The fair values below are gross values before netting agreements and netting of cash collateral.
	Great Plains Energy
		Balance Sheet		Asset Derivatives						Liability Derivatives
	June 30, 2014	Classification		Fair Value						Fair Value
	Derivatives Not Designated as Hedging Instruments				(millions)
	Commodity contracts	Other			$	12.9					$	8.3
	December 31, 2013
	Derivatives Not Designated as Hedging Instruments
	Commodity contracts	Other			$	8.5					$	1
	KCP&L
		Balance Sheet		Asset Derivatives						Liability Derivatives
	June 30, 2014	Classification		Fair Value						Fair Value
	Derivatives Not Designated as Hedging Instruments				(millions)
	Commodity contracts	Other			$	6.3					$	5.1
	31-Dec-13
	Derivatives Not Designated as Hedging Instruments
	Commodity contracts	Other			$	1.2					$	0.3
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-Jun-14	(millions)
	Derivative assets		$	12.9					$	(6.5	)				$	6.4			$	—		$	—		$	6.4
	Derivative liabilities		8.3						(6.5		)				1.8				—			—			1.8
	31-Dec-13
	Derivative assets		$	8.5					$	(0.7	)				$	7.8			$	—		$	—		$	7.8
	Derivative liabilities		1						(0.9		)				0.1				—			—			0.1
	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
	30-Jun-14	(millions)
	Derivative assets		$	6.3					$	(5.1	)				$	1.2			$	—		$	—		$	1.2
	Derivative liabilities		5.1						(5.1		)				—				—			—			—
	31-Dec-13
	Derivative assets		$	1.2					$	(0.1	)				$	1.1			$	—		$	—		$	1.1
	Derivative liabilities		0.3						(0.3		)				—				—			—			—
Schedule of Other Derivatives Not Designated as Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block]	'
	The following tables summarize the amounts of gain (loss) recognized for the change in fair value of commodity contract derivatives not designated as hedging instruments for Great Plains Energy and KCP&L.
	Great Plains Energy
		Three Months Ended									Year to Date
		30-Jun									30-Jun
	Derivatives Not Designated as Hedging Instruments		2014				2013				2014				2013
	Location of Gain (Loss)		(millions)
	Electric revenues		$	(3.2	)		$	—			$	(2.3	)		$	—
	Fuel		0.6				1.4				1				(0.6		)
	Purchased power		—				—				0.4				—
	Regulatory asset		(4.0		)		(0.7		)		(4.1		)		(1.6		)
	Regulatory liability		(0.9		)		—				0.2				—
	Total		$	(7.5	)		$	0.7			$	(4.8	)		$	(2.2	)
	KCP&L
		Three Months Ended									Year to Date
		30-Jun									30-Jun
	Derivatives Not Designated as Hedging Instruments		2014				2013				2014				2013
	Location of Gain (Loss)		(millions)
	Electric revenues		$	(3.2	)		$	—			$	(2.3	)		$	—
	Fuel		0.1				1.6				0.1				0.6
	Regulatory asset		(2.1		)		—				(2.2		)		—
	Total		$	(5.2	)		$	1.6			$	(4.4	)		$	0.6

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2014
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 at June 30, 2014, and December 31, 2013.
	Description	June 30						Netting(e)				Level 1			Level 2				Level 3
		2014
	KCP&L		(millions)
	Assets
	Nuclear decommissioning trust (a)
	Equity securities		$	135					$	—			$	135		$	—			$	—
	Debt securities
	U.S. Treasury		21.3						—				21.3			—				—
	U.S. Agency		4.9						—				—			4.9				—
	State and local obligations		4						—				—			4				—
	Corporate bonds		25.7						—				—			25.7				—
	Foreign governments		0.6						—				—			0.6				—
	Cash equivalents		3.4						—				3.4			—				—
	Other		(0.1		)				—				—			(0.1		)		—
	Total nuclear decommissioning trust		194.8						—				159.7			35.1				—
	Self-insured health plan trust (b)
	Equity securities		1.2						—				1.2			—				—
	Debt securities		8.4						—				—			8.4				—
	Cash and cash equivalents		5.8						—				5.8			—				—
	Total self-insured health plan trust		15.4						—				7			8.4				—
	Derivative instruments (c)		1.2						(5.1		)		0.3			—				6
	Total		211.4						(5.1		)		167			43.5				6
	Liabilities
	Derivative instruments (c)		—						(5.1		)		—			—				5.1
	Total		$	—					$	(5.1	)		$	—		$	—			$	5.1
	Other Great Plains Energy
	Assets
	Derivative instruments (c)		$	5.2					$	(1.4	)		$	0.4		$	3.5			$	2.7
	SERP rabbi trusts (d)
	Equity securities		0.1						—				0.1			—				—
	Fixed income funds		18						—				—			18				—
	Total SERP rabbi trusts		18.1						—				0.1			18				—
	Total		23.3						(1.4		)		0.5			21.5				2.7
	Liabilities
	Derivative instruments (c)		1.8						(1.4		)		0.2			—				3
	Total		$	1.8					$	(1.4	)		$	0.2		$	—			$	3
	Great Plains Energy
	Assets
	Nuclear decommissioning trust (a)		$	194.8					$	—			$	159.7		$	35.1			$	—
	Self-insured health plan trust (b)		15.4						—				7			8.4				—
	Derivative instruments (c)		6.4						(6.5		)		0.7			3.5				8.7
	SERP rabbi trusts (d)		18.1						—				0.1			18				—
	Total		234.7						(6.5		)		167.5			65				8.7
	Liabilities
	Derivative instruments (c)		1.8						(6.5		)		0.2			—				8.1
	Total		$	1.8					$	(6.5	)		$	0.2		$	—			$	8.1
	Description	December 31						Netting(e)				Level 1			Level 2				Level 3
		2013
	KCP&L		(millions)
	Assets
	Nuclear decommissioning trust (a)
	Equity securities		$	127.7					$	—			$	127.7		$	—			$	—
	Debt securities
	U.S. Treasury		21.2						—				21.2			—				—
	U.S. Agency		2.8						—				—			2.8				—
	State and local obligations		3.9						—				—			3.9				—
	Corporate bonds		24.4						—				—			24.4				—
	Foreign governments		0.5						—				—			0.5				—
	Cash equivalents		3.8						—				3.8			—				—
	Other		(0.4		)				—				—			(0.4		)		—
	Total nuclear decommissioning trust		183.9						—				152.7			31.2				—
	Self-insured health plan trust (b)
Equity securities		0.9						—				0.9			—				—
Debt securities		9.3						—				0.5			8.8				—
Cash and cash equivalents		3.4						—				3.4			—				—
Other		1.2						—				—			1.2				—
Total self-insured health plan trust		14.8						—				4.8			10				—
Derivative instruments (c)		1.1						(0.1		)		0.1			—				1.1
Total		199.8						(0.1		)		157.6			41.2				1.1
Liabilities
Derivative instruments (c)		—						(0.3		)		0.3			—				—
Total		$	—					$	(0.3	)		$	0.3		$	—			$	—
Other Great Plains Energy
Assets
Derivative instruments (c)		$	6.7					$	(0.6	)		$	0.2		$	4.9			$	2.2
SERP rabbi trusts (d)
Equity securities		0.1						—				0.1			—				—
Fixed income funds		18.6						—				—			18.6				—
Total SERP rabbi trusts		18.7						—				0.1			18.6				—
Total		25.4						(0.6		)		0.3			23.5				2.2
Liabilities
Derivative instruments (c)		0.1						(0.6		)		0.6			0.1				—
Total		$	0.1					$	(0.6	)		$	0.6		$	0.1			$	—
Great Plains Energy
Assets
Nuclear decommissioning trust (a)		$	183.9					$	—			$	152.7		$	31.2			$	—
Self-insured health plan trust (b)		14.8						—				4.8			10				—
Derivative instruments (c)		7.8						(0.7		)		0.3			4.9				3.3
SERP rabbi trusts (d)		18.7						—				0.1			18.6				—
Total		225.2						(0.7		)		157.9			64.7				3.3
Liabilities
Derivative instruments (c)		0.1						(0.9		)		0.9			0.1				—
Total		$	0.1					$	(0.9	)		$	0.9		$	0.1			$	—
(a)	Fair value is based on quoted market prices of the investments held by the fund and/or valuation models.
(b)	Fair value is based on quoted market prices of the investments held by the trust. Debt securities classified as Level 1 are comprised of U.S. Treasury securities. Debt securities classified as Level 2 are comprised of corporate bonds, U.S. Agency, state and local obligations, and other asset-backed securities.
(c)	The fair value of derivative instruments is estimated using market quotes, over-the-counter forward price and volatility curves and correlations among fuel prices, net of estimated credit risk. Derivative instruments classified as Level 1 represent exchange traded derivative instruments. Derivative instruments classified as Level 2 represent non-exchange traded derivative instruments traded in over-the-counter markets. Derivative instruments classified as Level 3 represent non-exchange traded derivatives traded in over-the-counter markets for which observable market data is not available to corroborate the valuation inputs and TCRs valued at the most recent auction price in the SPP Integrated Marketplace.
(d)	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.
(e)	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 December 31, 2013, Great Plains Energy netted $0.2 million 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.
	Great Plains Energy
	Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
		Derivative Instruments
		2014				2013
		(millions)
	Net asset at April 1	$	6.9			$	2.4
	Total realized/unrealized gains (losses):
	included in electric revenue	(3.2		)		—
	included in non-operating income	4				1.9
	included in regulatory asset	(4.1		)		—
	Purchases	7.3				—
	Settlements	(10.3		)		(2.4		)
	Net asset at June 30	$	0.6			$	1.9
	Total unrealized gains (losses) relating to assets still on the consolidated balance sheet at June 30:
	included in electric revenue	$	(2.4	)		$	—
	included in non-operating income	$	0.1			$	(0.3	)
	included in regulatory asset	$	(4.1	)		$	—
	Great Plains Energy
	Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
		Derivative Instruments
		2014				2013
		(millions)
	Net asset at January 1	$	3.3			$	2.3
	Total realized/unrealized gains (losses):
	included in electric revenue	(2.3		)		—
	included in purchased power expense	0.4				—
	included in non-operating income	11.1				4.3
	included in regulatory asset	(4.1		)		—
	Purchases	13.4				—
	Settlements	(21.2		)		(4.7		)
	Net asset at June 30	$	0.6			$	1.9
	Total unrealized gains (losses) relating to assets still on the consolidated balance sheet at June 30:
	included in electric revenue	$	(2.5	)		$	—
	included in non-operating income	$	0.2			$	(0.1	)
	included in regulatory asset	$	(4.1	)		$	—
	KCP&L
	Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
		Derivative Instruments
			2014
			(millions)
	Net asset at April 1		$	3.9
	Total realized/unrealized gains (losses):
	included in electric revenue		(3.2		)
	included in regulatory asset		(2.1		)
	Purchases		6.7
	Settlements		(4.4		)
	Net asset at June 30		$	0.9
	Total unrealized gains (losses) relating to assets still on the consolidated balance sheet at June 30:
	included in electric revenue		$	(2.4	)
	included in regulatory asset		$	(2.1	)
	KCP&L
	Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
		Derivative Instruments
			2014
			(millions)
	Net asset at January 1		$	1.1
	Total realized/unrealized gains (losses):
	included in electric revenue		(2.3		)
	included in regulatory asset		(2.2		)
	Purchases		11.8
	Settlements		(7.5		)
	Net asset at June 30		$	0.9
Total unrealized gains (losses) relating to assets still on the consolidated balance sheet at June 30:
included in electric revenue		$	(2.5	)
included in regulatory asset		$	(2.2	)

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [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)
	Year to Date June 30, 2014	(millions)
	Beginning balance January 1		$	(23.8	)				$	(1.5	)	$	(25.3	)
	Amounts reclassified from accumulated other comprehensive loss		5.3						0.2			5.5
	Net current period other comprehensive income		5.3						0.2			5.5
	Ending balance June 30		$	(18.5	)				$	(1.3	)	$	(19.8	)
	Year to Date June 30, 2013
	Beginning balance January 1		$	(35.4	)				$	(3.0	)	$	(38.4	)
	Amounts reclassified from accumulated other comprehensive loss		6.1						0.2			6.3
	Net current period other comprehensive income		6.1						0.2			6.3
	Ending balance June 30		$	(29.3	)				$	(2.8	)	$	(32.1	)
	(a) Net of tax
	KCP&L
		Gains and Losses on Cash Flow Hedges(a)
	Year to Date June 30, 2014	(millions)
	Beginning balance January 1		$	(20.2	)
	Amounts reclassified from accumulated other comprehensive loss		2.7
	Net current period other comprehensive income		2.7
	Ending balance June 30		$	(17.5	)
	Year to Date June 30, 2013
	Beginning balance January 1		$	(25.8	)
	Amounts reclassified from accumulated other comprehensive loss		2.8
	Net current period other comprehensive income		2.8
	Ending balance June 30		$	(23.0	)
	(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 June 30	2014				2013
		(millions)
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts	$	(3.9	)		$	(4.7	)		Interest charges
		(3.9		)		(4.7		)		Income before income tax expense and income (loss) from equity investments
		1.4				1.8				Income tax benefit
		$	(2.5	)		$	(2.9	)		Net income
	Amortization of defined benefit pension items
	Net losses included in net periodic benefit costs	(0.1		)		(0.3		)		Utility operating and maintenance expenses
		(0.1		)		(0.3		)		Income before income tax expense and income (loss) from equity investments
		0.1				0.1				Income tax benefit
		—				(0.2		)		Net income
	Total reclassifications, net of tax	$	(2.5	)		$	(3.1	)		Net income
	Year to Date June 30	2014				2013
		(millions)
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts	$	(8.6	)		$	(9.7	)		Interest charges
	Commodity contracts	—				(0.2		)		Fuel
		(8.6		)		(9.9		)		Income before income tax expense and income (loss) from equity investments
		3.3				3.8				Income tax benefit
		$	(5.3	)		$	(6.1	)		Net income
	Amortization of defined benefit pension items
	Net losses included in net periodic benefit costs	(0.3		)		(0.3		)		Utility operating and maintenance expenses
		(0.3		)		(0.3		)		Income before income tax expense and income (loss) from equity investments
		0.1				0.1				Income tax benefit
		(0.2		)		(0.2		)		Net income
	Total reclassifications, net of tax	$	(5.5	)		$	(6.3	)		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 June 30	2014				2013
		(millions)
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts	$	(2.2	)		$	(2.2	)		Interest charges
		(2.2		)		(2.2		)		Income before income tax expense
		0.8				0.9				Income tax benefit
	Total reclassifications, net of tax	$	(1.4	)		$	(1.3	)		Net income
	Year to Date June 30	2014				2013
		(millions)
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts	$	(4.4	)		$	(4.4	)		Interest charges
	Commodity contracts	—				(0.2		)		Fuel
		(4.4		)		(4.6		)		Income before income tax expense
		1.7				1.8				Income tax benefit
	Total reclassifications, net of tax	$	(2.7	)		$	(2.8	)		Net income

Taxes_Tables

Taxes (Tables)	6 Months Ended
	Jun. 30, 2014
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-Jun								30-Jun
	Great Plains Energy	2014				2013				2014			2013
	Current income taxes	(millions)
	Federal	$	(0.2	)		$	—			$	0.1		$	—
	State	—				0.2				0.1			0.1
	Total	(0.2		)		0.2				0.2			0.1
	Deferred income taxes
	Federal	25				27.6				31.6			37.5
	State	5.1				5.7				6.8			8
	Total	30.1				33.3				38.4			45.5
	Noncurrent income taxes
	Federal	(2.4		)		—				(2.4		)	—
	State	(0.3		)		(0.2		)		(0.3		)	(0.2		)
	Foreign	0.2				(0.2		)		—			(0.3		)
	Total	(2.5		)		(0.4		)		(2.7		)	(0.5		)
	Investment tax credit amortization	(0.4		)		(0.4		)		(0.8		)	(0.9		)
	Income tax expense	$	27			$	32.7			$	35.1		$	44.2
		Three Months Ended								Year to Date
		30-Jun								30-Jun
	KCP&L	2014				2013				2014			2013
	Current income taxes	(millions)
	Federal	$	(2.0	)		$	(0.3	)		$	0.7		$	(0.6	)
	State	(0.3		)		(0.1		)		0.2			(0.1		)
	Total	(2.3		)		(0.4		)		0.9			(0.7		)
	Deferred income taxes
	Federal	14.9				16.6				15.3			20.6
	State	3.3				3.7				3.9			5
	Total	18.2				20.3				19.2			25.6
	Noncurrent income taxes
	Federal	—				0.6				—			1.1
	State	—				0.1				—			0.2
	Total	—				0.7				—			1.3
	Investment tax credit amortization	(0.3		)		(0.3		)		(0.5		)	(0.5		)
	Income tax expense	$	15.6			$	20.3			$	19.6		$	25.7
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	'
	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-Jun						30-Jun
	Great Plains Energy	2014			2013			2014			2013
	Federal statutory income tax rate	35	%		35	%		35	%		35	%
	Differences between book and tax depreciation not normalized	(0.6	)		(0.3	)		(0.9	)		0.2
	Amortization of investment tax credits	(0.5	)		(0.4	)		(0.7	)		(0.6	)
	Federal income tax credits	(3.8	)		(3.8	)		(5.4	)		(5.0	)
	State income taxes	3.8			3.8			3.8			3.9
	Changes in uncertain tax positions, net	0.3			(0.3	)		—			(0.4	)
	Other	(0.2	)		(0.1	)		(0.3	)		(0.1	)
	Effective income tax rate	34	%		33.9	%		31.5	%		33	%
		Three Months Ended						Year to Date
		30-Jun						30-Jun
	KCP&L	2014			2013			2014			2013
	Federal statutory income tax rate	35	%		35	%		35	%		35	%
	Differences between book and tax depreciation not normalized	(0.9	)		(0.7	)		(1.8	)		(0.1	)
	Amortization of investment tax credits	(0.5	)		(0.4	)		(0.7	)		(0.6	)
	Federal income tax credits	(5.9	)		(5.7	)		(8.3	)		(7.7	)
	State income taxes	3.8			3.8			3.7			3.8
	Changes in uncertain tax positions, net	—			(0.1	)		—			(0.1	)
	Other	(0.5	)		(0.3	)		(0.6	)		(0.4	)
	Effective income tax rate	31	%		31.6	%		27.3	%		29.9	%
Summary of Income Tax Contingencies [Table Text Block]	'
	The following table reflects activity for Great Plains Energy related to the liability for unrecognized tax benefits.
		30-Jun						31-Dec
		2014						2013
		(millions)
	Beginning balance January 1		$	9.8					$	21.4
	Reductions for current year tax positions		(0.2		)				(0.3		)
	Reductions for prior year tax positions		(0.7		)				(10.5		)
	Statute expirations		—						(0.3		)
	Foreign currency translation adjustments		—						(0.5		)
	Ending balance		$	8.9					$	9.8

Segments_and_Related_Informati1

Segments and Related Information (Tables)	6 Months Ended
	Jun. 30, 2014
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-Jun-14	Utility												Energy
		(millions)
	Operating revenues		$	648.4			$	—			$	—			$	648.4
	Depreciation and amortization		(75.6		)		—				—				(75.6		)
	Interest (charges) income		(46.0		)		(11.7		)		9.4				(48.3		)
	Income tax (expense) benefit		(28.0		)		1				—				(27.0		)
	Net income (loss)		54.7				(2.6		)		—				52.1
	Year to Date	Electric				Other				Eliminations				Great Plains
	30-Jun-14	Utility												Energy
		(millions)
	Operating revenues		$	1,233.50			$	—			$	—			$	1,233.50
	Depreciation and amortization		(150.1		)		—				—				(150.1		)
	Interest (charges) income		(93.0		)		(24.3		)		19.6				(97.7		)
	Income tax (expense) benefit		(37.8		)		2.7				—				(35.1		)
	Net income (loss)		80.8				(4.9		)		—				75.9
	Three Months Ended	Electric				Other				Eliminations				Great Plains
	30-Jun-13	Utility												Energy
		(millions)
	Operating revenues		$	600.3			$	—			$	—			$	600.3
	Depreciation and amortization		(72.6		)		—				—				(72.6		)
	Interest (charges) income		(47.4		)		(14.6		)		12.6				(49.4		)
	Income tax (expense) benefit		(33.9		)		1.2				—				(32.7		)
	Net income (loss)		65.5				(1.9		)		—				63.6
	Year to Date	Electric				Other				Eliminations				Great Plains
	30-Jun-13	Utility												Energy
		(millions)
	Operating revenues		$	1,142.50			$	—			$	—			$	1,142.50
	Depreciation and amortization		(142.8		)		—				—				(142.8		)
	Interest (charges) income		(95.2		)		(29.1		)		25.2				(99.1		)
	Income tax (expense) benefit		(46.5		)		2.3				—				(44.2		)
	Net income (loss)		93.1				(3.5		)		—				89.6
		Electric				Other				Eliminations				Great Plains
		Utility												Energy
	June 30, 2014		(millions)
	Assets		$	10,325.70			$	120.8			$	(388.4	)		$	10,058.10
	Capital expenditures(a)		352.9				—				—				352.9
	December 31, 2013
	Assets		$	10,019.60			$	105.6			$	(329.8	)		$	9,795.40
	Capital expenditures(a)		669				—				—				669
	(a) Capital expenditures reflect year to date amounts for the periods presented.

Summary_of_Significant_Account3

Summary of Significant Accounting Policies Antidilutive Securities (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Performance Shares [Member]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	475,549	55,271	475,549	55,271
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	0	287	21,652

Summary_of_Significant_Account4

Summary of Significant Accounting Policies Earnings Per Share (Details) (USD $)	3 Months Ended		6 Months Ended
In Millions, except Per Share data, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accounting Policies [Abstract]	'	'	'	'
Net income (loss)	$52.10	$63.60	$75.90	$89.60
Income [Abstract]	'	'	'	'
Less: preferred stock dividend requirements	0.4	0.4	0.8	0.8
Earnings (loss) available for common shareholders	$51.70	$63.20	$75.10	$88.80
Common Shares Outstanding [Abstract]	'	'	'	'
Average number of common shares outstanding (in shares)	153.8	153.5	153.8	153.4
Add: effect of dilutive securities (in shares)	0.2	0.3	0.2	0.3
Diluted average number of common shares outstanding (in shares)	154	153.8	154	153.7
Earnings Per Share [Abstract]	'	'	'	'
Earnings Per Share, Basic and Diluted	$0.34	$0.41	$0.49	$0.58

Summary_of_Significant_Account5

Summary of Significant Accounting Policies Fair Value of Financial Instruments (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Billions, unless otherwise specified
Carrying (Reported) Amount, Fair Value Disclosure [Member]	'	'
Fair value of financial instruments [Abstract]	'	'
Long-term Debt	$3.50	$3.50
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	2.3
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]	'	'
Fair value of financial instruments [Abstract]	'	'
Long-term Debt, Fair Value	3.9	3.7
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Kansas City Power and Light Company [Member]	'	'
Fair value of financial instruments [Abstract]	'	'
Long-term Debt, Fair Value	$2.60	$2.50

Summary_of_Significant_Account6

Summary of Significant Accounting Policies Subsequent Events (Details) (Dividend Declared [Member], USD $)	0 Months Ended
	Aug. 05, 2014	Aug. 05, 2014
Kansas City Power and Light Company [Member]	'	'
Dividends Declared [Abstract]	'	'
Dividends Payable, Amount Per Share	'	$18,000,000
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	'

Summary_of_Significant_Account7

Summary of Significant Accounting Policies Summary of Significant Accounting Policies Utility Plant (Details) (USD $)	3 Months Ended		6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Public Utility, Property, Plant and Equipment [Line Items]	'	'	'	'	'
Depreciation and amortization	$75.60	$72.60	$150.10	$142.80	'
Utility Plant, at original cost	'	'	'	'	'
Public Utilities, Property, Plant and Equipment, Plant in Service	11,924.20	'	11,924.20	'	11,575.30
Kansas City Power and Light Company [Member]	'	'	'	'	'
Public Utility, Property, Plant and Equipment [Line Items]	'	'	'	'	'
Depreciation and amortization	52.6	49.6	104.3	97.2	'
Utility Plant, at original cost	'	'	'	'	'
Public Utilities, Property, Plant and Equipment, Plant in Service	$8,578.90	'	$8,578.90	'	$8,274.90

Summary_of_Significant_Account8

Summary of Significant Accounting Policies Equity Method Investment (Details) (Transource Energy, LLC [Member])	3 Months Ended
	Mar. 31, 2014
Schedule of Equity Method Investments [Line Items]	'
Equity Method Investment, Description of Principal Activities	'Transource is focused on the development of competitive electric transmission projects.
GPE Transmission Holding Company, LLC [Member]	'
Schedule of Equity Method Investments [Line Items]	'
Equity Method Investment, Ownership Percentage	13.50%
AEP Transmission Holding Company, LLC [Member]	'
Schedule of Equity Method Investments [Line Items]	'
Ownership Percentage of Majority Owner	86.50%

Supplemental_Cash_Flow_Informa2

Supplemental Cash Flow Information (Details) (USD $)	6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
Cash flows affected by changes in:	'	'
Receivables	($57.10)	($25.90)
Accounts receivable pledged as collateral	4	-1
Fuel inventories	3.9	-7.2
Materials and supplies	4.1	-2.1
Accounts payable	-76.1	-116.3
Accrued taxes	46	43.7
Accrued interest	-1.3	-0.2
Deferred refueling outage costs	8.4	-26.4
Pension and post-retirement benefit obligations	5.3	21
Allowance for equity funds used during construction	-9	-5
Fuel recovery mechanism	-17.3	-6.4
Solar rebates paid	-33.3	-11.8
Other operating activities	-5.5	-1.8
Total other operating activities	-127.9	-139.4
Cash paid during the period:	'	'
Interest Paid, Net	88.2	87.2
Income Taxes Paid	0.1	0.2
Non-cash investing activities:	'	'
Liabilities accrued for capital expenditures	46.7	32.8
Kansas City Power and Light Company [Member]	'	'
Cash flows affected by changes in:	'	'
Receivables	-34.4	-5.2
Fuel inventories	6.6	-7.5
Materials and supplies	2.8	-1.7
Accounts payable	-38.8	-85.8
Accrued taxes	31.9	29.8
Accrued interest	-1.5	0.1
Deferred refueling outage costs	8.4	-26.4
Pension and post-retirement benefit obligations	4.4	22.3
Allowance for equity funds used during construction	-8.5	-5
Fuel recovery mechanism	2.4	-3.1
Solar rebates paid	-10.7	-3
Other operating activities	-15.8	-7.7
Total other operating activities	-53.2	-93.2
Cash paid during the period:	'	'
Interest Paid, Net	57.2	57.4
Non-cash investing activities:	'	'
Liabilities accrued for capital expenditures	$39.30	$29.20

Receivables_Details

Receivables (Details) (USD $)	3 Months Ended				6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Accounts Receivable Sold [Line Items]	'		'		'		'
Receivables (sold) purchased	$0		$0		$0		$0
Gain (Loss) on Sale of Accounts Receivable	-0.7	[1]	-0.6	[1]	-0.6	[1]	-0.6	[1]
Servicing fees received (paid)	0		0		0		0
Fees paid to outside investor	-0.4		-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
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	-0.4	[1]	-0.4	[1]	-0.3	[1]	-0.4	[1]
Servicing fees received (paid)	0		0		0		0
Fees paid to outside investor	-0.3		-0.3		-0.6		-0.6
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
Kansas City Power And Light Company Unconsolidated [Member]	'		'		'		'
Accounts Receivable Sold [Line Items]	'		'		'		'
Receivables (sold) purchased	-380.9		-373.3		-734		-708
Gain (Loss) on Sale of Accounts Receivable	-4.8	[1]	-4.8	[1]	-9.3	[1]	-9	[1]
Servicing fees received (paid)	0.6		0.6		1.2		1.2
Fees paid to outside investor	0		0		0		0
Cash from customers (transferred) received	-348.2		-345.6		-715.8		-682.3
Cash received from (paid for) receivables purchased	343.8		341.3		706.8		673.8
Intercompany interest income (expense) on notes	0.1		'		0.1		0.1
KCPL Receivables Company [Member]	'		'		'		'
Accounts Receivable Sold [Line Items]	'		'		'		'
Receivables (sold) purchased	380.9		373.3		734		708
Gain (Loss) on Sale of Accounts Receivable	4.4	[1]	4.4	[1]	9	[1]	8.6	[1]
Servicing fees received (paid)	-0.6		-0.6		-1.2		-1.2
Fees paid to outside investor	-0.3		-0.3		-0.6		-0.6
Cash from customers (transferred) received	348.2		345.6		715.8		682.3
Cash received from (paid for) receivables purchased	-343.8		-341.3		-706.8		-673.8
Intercompany interest income (expense) on notes	-0.1		'		-0.1		-0.1
KCPL Greater Missouri Operations [Member]	'		'		'		'
Accounts Receivable Sold [Line Items]	'		'		'		'
Receivables (sold) purchased	-197.9		-202.7		-391.7		-388.1
Gain (Loss) on Sale of Accounts Receivable	-2.5	[1]	-2.6	[1]	-5	[1]	-4.9	[1]
Servicing fees received (paid)	0.3		0.3		0.6		0.6
Fees paid to outside investor	0		0		0		0
Cash from customers (transferred) received	-176.5		-184.6		-377.3		-369.5
Cash received from (paid for) receivables purchased	174.3		182.3		372.6		364.9
Intercompany interest income (expense) on notes	0		'		0		0
GMO Receivables Company Member	'		'		'		'
Accounts Receivable Sold [Line Items]	'		'		'		'
Receivables (sold) purchased	197.9		202.7		391.7		388.1
Gain (Loss) on Sale of Accounts Receivable	2.2	[1]	2.4	[1]	4.7	[1]	4.7	[1]
Servicing fees received (paid)	-0.3		-0.3		-0.6		-0.6
Fees paid to outside investor	-0.1		0		-0.3		-0.3
Cash from customers (transferred) received	176.5		184.6		377.3		369.5
Cash received from (paid for) receivables purchased	-174.3		-182.3		-372.6		-364.9
Intercompany interest income (expense) on notes	$0		'		$0		$0
[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.

Receivables_Accounts_Notes_and

Receivables Accounts, Notes, and Financing (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Other Receivables, Gross, Current	$103.40	$88.60
Receivables, net	219.3	162.2
Kansas City Power and Light Company [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Other Receivables, Gross, Current	87.9	77.8
Receivables, net	161.3	129.2
Trade Accounts Receivable [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Allowance for doubtful accounts	-4.5	-2.5
Trade Accounts Receivable [Member] | Kansas City Power and Light Company [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Allowance for doubtful accounts	-2.5	-1.1
Trade Accounts Receivable [Member] | Billed Revenues [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Accounts Receivable, Gross, Current	9.4	1.5
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	6.4	1.3
Trade Accounts Receivable [Member] | Unbilled Revenues [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Accounts Receivable, Gross, Current	111	74.6
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	$69.50	$51.20

Receivables_Narrative_Details

Receivables Narrative (Details) (USD $)	6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Accounts receivable pledged as collateral	$171	$175
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	171	175
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	'

Nuclear_Plant_Details

Nuclear Plant (Details) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Dec. 31, 2012
Investments in decommissioning trust fund [Line Items]	'	'	'	'	'	'
Cost Basis	$141.70	'	$141.70	'	$138.10	'
Gross Unrealized Gains	'	'	53.6	'	47.1	'
Gross Unrealized Losses	'	'	-0.5	'	-1.3	'
Fair Value, Nuclear decommissioning trust fund	194.8	'	194.8	'	183.9	154.7
Weighted average maturity of debt securities (in years)	7	'	7	'	'	'
Realized gains on investments in decommissioning trust fund	0.5	0.4	0.7	1.9	'	'
Realized losses on investments in decommissioning trust fund	-0.5	0	-0.6	-0.4	'	'
Equity Securities [Member]	'	'	'	'	'	'
Investments in decommissioning trust fund [Line Items]	'	'	'	'	'	'
Cost Basis	85.3	'	85.3	'	83.7	'
Gross Unrealized Gains	'	'	50.1	'	44.6	'
Gross Unrealized Losses	'	'	-0.4	'	-0.6	'
Fair Value, Nuclear decommissioning trust fund	135	'	135	'	127.7	'
Debt Securities [Member]	'	'	'	'	'	'
Investments in decommissioning trust fund [Line Items]	'	'	'	'	'	'
Cost Basis	53.1	'	53.1	'	51	'
Gross Unrealized Gains	'	'	3.5	'	2.5	'
Gross Unrealized Losses	'	'	-0.1	'	-0.7	'
Fair Value, Nuclear decommissioning trust fund	56.5	'	56.5	'	52.8	'
Other Securities [Member]	'	'	'	'	'	'
Investments in decommissioning trust fund [Line Items]	'	'	'	'	'	'
Cost Basis	3.3	'	3.3	'	3.4	'
Gross Unrealized Gains	'	'	0	'	0	'
Gross Unrealized Losses	'	'	0	'	0	'
Fair Value, Nuclear decommissioning trust fund	3.3	'	3.3	'	3.4	'
Kansas City Power and Light Company [Member]	'	'	'	'	'	'
Investments in decommissioning trust fund [Line Items]	'	'	'	'	'	'
Fair Value, Nuclear decommissioning trust fund	$194.80	'	$194.80	'	$183.90	$154.70

Nuclear_Plant_Decommissioning_

Nuclear Plant Decommissioning Trust (Details) (USD $)	6 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Nuclear decommissioning trust fund [Roll Forward]	'	'
Nuclear decommissioning trust fund, beginning balance	$183.90	$154.70
Contributions to nuclear decommissioning trust fund	1.6	3.3
Earned income, net of fees	1.9	2.7
Net realized gains (losses) on nuclear decommissioning trust fund	0.1	1.7
Net unrealized gains (losses) on nuclear decommissioning trust fund	7.3	21.5
Nuclear decommissioning trust fund, ending balance	194.8	183.9
Kansas City Power and Light Company [Member]	'	'
Nuclear decommissioning trust fund [Roll Forward]	'	'
Nuclear decommissioning trust fund, beginning balance	183.9	154.7
Contributions to nuclear decommissioning trust fund	1.6	3.3
Earned income, net of fees	1.9	2.7
Net realized gains (losses) on nuclear decommissioning trust fund	0.1	1.7
Net unrealized gains (losses) on nuclear decommissioning trust fund	7.3	21.5
Nuclear decommissioning trust fund, ending balance	$194.80	$183.90
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%	'

Regulatory_Matters_Details

Regulatory Matters (Details) (USD $)	1 Months Ended	6 Months Ended	0 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Jun. 30, 2014	Jan. 09, 2013	Jan. 09, 2013
	Kansas City Power and Light Company [Member]	Kansas City Power and Light Company [Member]	KCPL Greater Missouri Operations [Member]	KCPL Greater Missouri Operations [Member]
	Kansas Corporation Commission [Member]	Kansas Corporation Commission [Member]	Missouri Public Service Commission [Member]	Missouri Public Service Commission [Member]
			St Joseph Light and Power division [Member]	Missouri Public Service division [Member]
Regulatory Proceedings [Line Items]	'	'	'	'
Annual revenue increase, requested	$12.10	'	'	'
Revised annual revenue increase, requested	'	11.5	'	'
Annual revenue increase authorized	'	'	$21.70	$26.20

Regulatory_Matters_Asset_Detai

Regulatory Matters Asset (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Regulatory Assets [Line Items]	'	'
Regulatory Assets, Noncurrent	$867.60	$849.70
Kansas City Power and Light Company [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory Assets, Noncurrent	$591	$614.10

Regulatory_Matters_Liabilities

Regulatory Matters Liabilities (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities	$282.50	$264
Kansas City Power and Light Company [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities	$174	$168.30

Regulatory_Matters_Regulatory_

Regulatory Matters Regulatory Matters Subsequent Events (Details) (Kansas City Power and Light Company [Member], Kansas Corporation Commission [Member], Subsequent Event [Member], USD $)	1 Months Ended
In Millions, unless otherwise specified	Jul. 31, 2014
Kansas City Power and Light Company [Member] | Kansas Corporation Commission [Member] | Subsequent Event [Member]	'
Subsequent Event [Line Items]	'
Annual revenue increase authorized	$11.50

Pension_Plans_and_Other_Employ2

Pension Plans and Other Employee Benefits (Details) (USD $)

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Jun. 30, 2013

Jun. 30, 2014

Jun. 30, 2013

Jun. 30, 2014

Jun. 30, 2013

Jun. 30, 2014

Jun. 30, 2013

In Millions, unless otherwise specified

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Pension Plans, Defined Benefit [Member]

Pension Plans, Defined Benefit [Member]

Pension Plans, Defined Benefit [Member]

Pension Plans, Defined Benefit [Member]

Other Postretirement Benefit Plans, Defined Benefit [Member]

Other Postretirement Benefit Plans, Defined Benefit [Member]

Other Postretirement Benefit Plans, Defined Benefit [Member]

Other Postretirement Benefit Plans, Defined Benefit [Member]

Defined Benefit Plan Disclosure [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Defined Benefit Plan, Contributions by Employer

'

'

'

'

'

'

$46.10

'

'

'

'

'

Amounts recognized in the consolidated balance sheets [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

Pension and Other Postretirement Defined Benefit Plans, Current Liabilities

-3.2

-3.2

-1.9

-1.9

'

'

'

'

'

'

'

'

Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent

-335.2

-360.5

-314.8

-339.9

'

'

'

'

'

'

'

'

Components of net periodic benefit costs [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

Defined Benefit Plan, Service Cost

'

'

'

'

9

10.5

18.1

21

0.9

1.1

1.8

2.2

Defined Benefit Plan, Interest Cost

'

'

'

'

12.7

11.8

25.4

23.6

2

1.9

4

3.8

Defined Benefit Plan, Expected Return on Plan Assets

'

'

'

'

-12.7

-11.8

-25.4

-23.6

-0.7

-0.5

-1.4

-1

Defined Benefit Plan, Amortization of Prior Service Cost (Credit)

'

'

'

'

0.2

0.5

0.4

1

0.8

1.8

1.6

3.6

Defined Benefit Plan, Amortization of Gains (Losses)

'

'

'

'

12.4

13.7

24.8

27.4

0

0.4

0

0.9

Defined Benefit Plan, Amortization of Transition Obligations (Assets)

'

'

'

'

0

0

0

0

0.1

0.1

0.1

0.1

Net periodic benefit costs before regulatory adjustment

'

'

'

'

21.6

24.7

43.3

49.4

3.1

4.8

6.1

9.6

Defined benefit plan, regulatory adjustment

'

'

'

'

-0.4

-2.8

-0.8

-6.4

1.1

-0.6

2.2

-1.1

Defined Benefit Plan, Net Periodic Benefit Cost

'

'

'

'

21.2

21.9

42.5

43

4.2

4.2

8.3

8.5

Contribute to plans in next year

'

'

'

'

'

'

$16.10

'

'

'

$11.30

'

Equity_Compensation_Details

Equity Compensation (Details) (USD $)	3 Months Ended			6 Months Ended
In Millions, except Share data, unless otherwise specified	Jun. 30, 2014		Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'		'
Equity compensation expense	$1		$0.30	$5.40		$2.10
Income tax benefit	0.3		0.1	2		0.7
Performance Shares [Member]	'		'	'		'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'		'
Expected volatility	'		'	18.00%		'
Expected dividend yield	'		'	3.56%		'
Risk-free interest rate	'		'	0.63%		'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]	'		'	'		'
Beginning balance (in shares)	'		'	430,009		'
Granted (in shares)	'		'	214,654		'
Earned (in shares)	'		'	-107,741		'
Performance adjustment (in shares)	'		'	-271		'
Forfeited (in shares)	'		'	-975		'
Ending balance (in shares)	535,676		'	535,676		'
Weighted average beginning balance (in dollars per share)	'		'	$23.52	[1]	'
Weighted average granted (in dollars per share)	$0		$0	$28.78	[1]	$24.16
Weighted average earned (in dollars per share)	'		'	$26.14	[1]	'
Weighted average forfeited (in dollars per share)	'		'	$24.33	[1]	'
Weighted average ending balance (in dollars per share)	$25.11	[1]	'	$25.11	[1]	'
Total unrecognized compensation expense	12.5		'	12.5		'
Remaining weighted-average contractual term (in years)	'		'	'1 year 8 months		'
Fair value of performance shares earned and paid	'		'	2.8		2.4
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)	'		'	288,537		'
Granted (in shares)	'		'	73,860		'
Vested (in shares)	'		'	-75,789		'
Forfeited (in shares)	'		'	-612		'
Ending balance (in shares)	285,996		'	285,996		'
Weighted average beginning balance (in dollars per share)	'		'	$20.18	[1]	'
Weighted average granted (in dollars per share)	$25.54		$0	$25.72	[1]	$22.45
Weighted average vested (in dollars per share)	'		'	$19.27	[1]	'
Weighted average forfeited (in dollars per share)	'		'	$24.16	[1]	'
Weighted average ending balance (in dollars per share)	$21.85	[1]	'	$21.85	[1]	'
Total unrecognized compensation expense	3		'	3		'
Total fair value of shares vested	0.2		'	1.5		0.6
Remaining weighted-average contractual term (in years)	'		'	'1 year 6 months		'
Kansas City Power and Light Company [Member]	'		'	'		'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'	'		'
Equity compensation expense	0.7		0.2	3.8		1.5
Income tax benefit	$0.30		$0	$1.40		$0.40
[1]	weighted-average

Shortterm_Borrowings_and_Short1

Short-term Borrowings and Short-term Bank Lines of Credit (Details) (USD $)	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Short-term Debt [Line Items]	'	'
Amount of outstanding cash borrowings	$0	$9,000,000
Commercial paper outstanding	376,500,000	108,200,000
Parent Company [Member] | Revolving Credit Facility [Member]	'	'
Short-term Debt [Line Items]	'	'
Amount of revolving credit facility	200,000,000	'
Revolving credit facility expiration date	1-Oct-18	'
Maximum borrowing capacity with transfer of unused commitments	400,000,000	'
Covenant term - amount considered in default	50,000,000	'
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	9,000,000
Weighted-average interest rate from outstanding borrowings	'	1.94%
Amount of letters of credit outstanding	0	0
Kansas City Power and Light Company [Member]	'	'
Short-term Debt [Line Items]	'	'
Commercial paper outstanding	288,300,000	93,200,000
Weighted-average interest rate from outstanding borrowings	0.29%	0.29%
Kansas City Power and Light Company [Member] | Revolving Credit Facility [Member]	'	'
Short-term Debt [Line Items]	'	'
Amount of revolving credit facility	600,000,000	'
Revolving credit facility expiration date	1-Oct-18	'
Maximum transfer of unused commitments	200,000,000	'
Covenant term - amount considered in default	50,000,000	'
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
Amount of letters of credit outstanding	2,700,000	3,800,000
KCPL Greater Missouri Operations [Member]	'	'
Short-term Debt [Line Items]	'	'
Commercial paper outstanding	88,200,000	15,000,000
Weighted-average interest rate from outstanding borrowings	0.28%	0.66%
KCPL Greater Missouri Operations [Member] | Revolving Credit Facility [Member]	'	'
Short-term Debt [Line Items]	'	'
Amount of revolving credit facility	450,000,000	'
Revolving credit facility expiration date	1-Oct-18	'
Maximum transfer of unused commitments	200,000,000	'
Covenant term - amount considered in default	50,000,000	'
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
Amount of letters of credit outstanding	$3,600,000	$16,400,000

LongTerm_Debt_Details

Long-Term Debt (Details) (USD $)

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

1 Months Ended

1 Months Ended

6 Months Ended

6 Months Ended

6 Months Ended

In Millions, unless otherwise specified

Jun. 30, 2014

Jun. 30, 2013

Dec. 31, 2013

Jun. 30, 2014

Jun. 30, 2013

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jan. 31, 2014

Jun. 30, 2014

Dec. 31, 2013

Jan. 31, 2014

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Jun. 30, 2014

Dec. 31, 2013

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

Kansas City Power and Light Company [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

KCPL Greater Missouri Operations [Member]

Parent Company [Member]

Parent Company [Member]

Parent Company [Member]

Parent Company [Member]

Parent Company [Member]

Parent Company [Member]

Other Consolidated Entities [Member]

Other Consolidated Entities [Member]

Secured Debt [Member]

Secured Debt [Member]

Secured Debt [Member]

Secured Debt [Member]

Secured Debt [Member]

Secured Debt [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Unsecured Debt [Member]

Unsecured Debt [Member]

Unsecured Debt [Member]

Unsecured Debt [Member]

Secured Debt [Member]

Secured Debt [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Medium-term Notes [Member]

Medium-term Notes [Member]

Medium-term Notes [Member]

Medium-term Notes [Member]

Unsecured Debt [Member]

Unsecured Debt [Member]

Unsecured Debt [Member]

Unsecured Debt [Member]

Unsecured Debt [Member]

Unsecured Debt [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

Senior Notes [Member]

General Mortgage bonds EIRR due 2015-2035 [Member]

General Mortgage bonds EIRR due 2015-2035 [Member]

General Mortgage bonds Series 2009 due 2019 [Member]

General Mortgage bonds Series 2009 due 2019 [Member]

General Mortgage bonds EIRR series 2005 due 2035 [Member]

General Mortgage bonds EIRR series 2005 due 2035 [Member]

Senior notes due 2017 KCPL [Member]

Senior notes due 2017 KCPL [Member]

Senior notes due 2018 KCPL [Member]

Senior notes due 2018 KCPL [Member]

Senior Notes due 2023 KCPL [Member]

Senior Notes due 2023 KCPL [Member]

Senior notes due 2035 KCPL [Member]

Senior notes due 2035 KCPL [Member]

Senior Notes Due 2041 KCPL [Member]

Senior Notes Due 2041 KCPL [Member]

EIRR Bonds Series 2007A and 2007B due 2035 [Member]

EIRR Bonds Series 2007A and 2007B due 2035 [Member]

EIRR bonds 2.875 percent Series 2008 [Member]

EIRR bonds 2.875 percent Series 2008 [Member]

First Mortgage Bonds due through 2021 [Member]

First Mortgage Bonds due through 2021 [Member]

Senior notes 8.27 percent series due 2021 [Member]

Senior notes 8.27 percent series due 2021 [Member]

Senior Notes Series A due 2025 [Member]

Senior Notes Series A due 2025 [Member]

Senior Notes Series B due 2033 [Member]

Senior Notes Series B due 2033 [Member]

Senior Notes Series C due 2043 [Member]

Senior Notes Series C due 2043 [Member]

Medium term notes 7.33 percent series due 2023 [Member]

Medium term notes 7.33 percent series due 2023 [Member]

Medium term notes 7.17 percent series due 2023 [Member]

Medium term notes 7.17 percent series due 2023 [Member]

Pollution control bonds Wamego Series 1996 due 2026 [Member]

Pollution control bonds Wamego Series 1996 due 2026 [Member]

Pollution control bonds Wamego Series 1996 due 2026 [Member]

Pollution control bonds state environmental 1993 due 2028 [Member]

Pollution control bonds state environmental 1993 due 2028 [Member]

Pollution control bonds state environmental 1993 due 2028 [Member]

Senior notes due 2017 [Member]

Senior notes due 2017 [Member]

Senior Notes Due 2021 [Member]

Senior Notes Due 2021 [Member]

Senior Notes Due 2022 [Member]

Senior Notes Due 2022 [Member]

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Principal outstanding

'

'

'

'

'

'

$146.40

$146.40

$400

$400

$50

$50

$250

$250

$350

$350

$300

$300

$250

$250

$400

$400

$146.50

$146.50

$23.40

$23.40

$7.90

$9

$80.90

$80.90

$125

$125

$75

$75

$150

$150

$3

$3

$7

$7

'

$0

$7.30

'

$0

$5

$100

$100

$350

$350

$287.50

$287.50

'

'

Debt Instrument, Maturity Date

'

'

'

'

'

'

'

'

31-Dec-19

'

31-Dec-35

'

31-Dec-17

'

31-Dec-18

'

31-Dec-23

'

31-Dec-35

'

31-Dec-41

'

31-Dec-35

'

31-Dec-38

'

'

'

31-Dec-21

'

31-Dec-25

'

31-Dec-33

'

31-Dec-43

'

31-Dec-23

'

31-Dec-23

'

'

'

'

'

'

'

31-Dec-17

'

31-Dec-21

'

31-Dec-22

'

'

'

Current maturities

-15.1

'

-1.1

-14

'

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-1.1

-1.1

Unamortized discount

'

'

'

-4

'

-4.1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unarmortized discount and premium, net

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4.6

4.9

Long-term debt excluding current maturities

3,488.10

'

3,515.70

2,298.30

'

2,312.20

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument Maturity Date Range Start

'

'

'

'

'

'

31-Dec-15

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

31-Dec-15

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument Maturity Date Range End

'

'

'

'

'

'

31-Dec-35

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

31-Dec-21

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rates (in hundredths)

'

'

'

'

'

'

'

'

7.15%

'

4.65%

'

5.85%

'

6.38%

'

3.15%

'

6.05%

'

5.30%

'

'

'

2.88%

'

9.44%

'

8.27%

'

3.49%

'

4.06%

'

4.74%

'

7.33%

'

7.17%

'

'

'

'

'

'

'

6.88%

'

4.85%

'

5.29%

'

'

'

Long-term Debt, Weighted Average Interest Rate

'

'

'

'

'

'

2.95%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Variable rate (in hundredths)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.06%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)

'

'

'

'

'

'

'

'

8.59%

'

'

'

5.72%

'

7.49%

'

'

'

5.78%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

7.33%

'

'

'

'

'

'

'

Repayments of Long-term Debt

$13.40

$9.30

'

$0

$2.60

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$7.30

'

'

$5

'

'

'

'

'

'

'

'

'

'

Assets_Held_for_Sale_Assets_He1

Assets Held for Sale Assets Held for Sale (Details) (USD $)	1 Months Ended	6 Months Ended
In Millions, unless otherwise specified	Jan. 31, 2014	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Assets held for sale	'	$0	'	$36.20
Proceeds from sale of assets	37.7	37.7	0	'
Kansas City Power and Light Company [Member]	'	'	'	'
Assets held for sale	'	0	'	4.7
Proceeds from sale of assets	$4.70	$4.70	$0	'

Commitments_and_Contingencies_

Commitments and Contingencies Environmental Matters (Details) (USD $)	6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
	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	'
EPA proposed nationwide CO2 emission reductions by 2030	30.00%	'
Remediation [Abstract]	'	'
Accrued environmental remediation expenses	1.4	1.4
MISSOURI	'	'
Climate Change [Abstract]	'	'
EPA proposed interim CO2 goal rate reduction	17.00%	'
EPA proposed CO2 emission reductions by 2030 by state	21.00%	'
KANSAS	'	'
Climate Change [Abstract]	'	'
EPA proposed interim CO2 goal rate reduction	19.00%	'
EPA proposed CO2 emission reductions by 2030 by state	23.00%	'
Jeffrey Units Nos 1 and 2 [Member]	'	'
New Source Review [Abstract]	'	'
Estimated cost to install a selective catalytic reduction system at Jeffrey Energy Center pursuant to a settlement agreement	230	'
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]	'	'
Cash capital expenditures incurred for La Cygne environmental project	433	'
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)	18,000,000	'
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	$1.30	'
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%	'

Legal_Proceedings_Loss_Conting

Legal Proceedings Loss Contingencies (Details) (Pending Litigation [Member], USD $)	6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014
Pending Litigation [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		6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
KCPL Greater Missouri Operations [Member]	'	'	'	'	'
Related Party Transaction [Line Items]	'	'	'	'	'
Related Party Transaction, Due from (to) Related Party, Current	$33.70	'	$33.70	'	$32.70
KCPL employees manage GMO's business and operate its facilities at cost	42.6	51.7	87.2	103.6	'
KCPL net wholesale sales to GMO	0.6	4.6	11	10	'
Great Plains Energy [Member]	'	'	'	'	'
Related Party Transaction [Line Items]	'	'	'	'	'
Related Party Transaction, Due from (to) Related Party, Current	19	'	19	'	17.5
Great Plains Energy [Member] | Money Pool [Member]	'	'	'	'	'
Related Party Transaction [Line Items]	'	'	'	'	'
Payable to Related Party	'	'	'	'	$0.20

Derivative_Instruments_Details

Derivative Instruments (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Futures contracts [Member] | Not Designated as Hedging Instrument [Member]	'	'
Price Risk Derivatives [Abstract]	'	'
Notional Contract Amount	$22.60	$19.30
Fair Value	0.4	-0.6
Forward Contracts [Member] | Not Designated as Hedging Instrument [Member]	'	'
Price Risk Derivatives [Abstract]	'	'
Notional Contract Amount	46.5	47.7
Fair Value	5	5.2
Option contracts [Member] | Not Designated as Hedging Instrument [Member]	'	'
Price Risk Derivatives [Abstract]	'	'
Notional Contract Amount	1.2	4.8
Fair Value	0.1	1.2
Transmission Congestion Rights [Member] | Not Designated as Hedging Instrument [Member]	'	'
Price Risk Derivatives [Abstract]	'	'
Notional Contract Amount	72.5	22.9
Fair Value	-0.9	1.7
Kansas City Power and Light Company [Member] | Futures contracts [Member] | Not Designated as Hedging Instrument [Member]	'	'
Price Risk Derivatives [Abstract]	'	'
Notional Contract Amount	13.4	7.7
Fair Value	0.2	-0.2
Kansas City Power and Light Company [Member] | Option contracts [Member] | Not Designated as Hedging Instrument [Member]	'	'
Price Risk Derivatives [Abstract]	'	'
Notional Contract Amount	1.2	0
Fair Value	0.1	0
Kansas City Power and Light Company [Member] | Transmission Congestion Rights [Member] | Not Designated as Hedging Instrument [Member]	'	'
Price Risk Derivatives [Abstract]	'	'
Notional Contract Amount	58.5	18
Fair Value	$0.90	$1.10
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 remainder of fiscal year	23.00%	'
Percentage of expected on peak natural gas and natural gas equivalent purchased power price exposure hedged year one	12.00%	'

Derivative_Instruments_Cash_Fl

Derivative Instruments Cash Flow Hedge (Details) (USD $)	6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014
Derivative [Line Items]	'
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$9.20
Kansas City Power and Light Company [Member]	'
Derivative [Line Items]	'
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$8.80

Derivative_Instruments_Derivat

Derivative Instruments Derivative Instruments Offsetting (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Derivative Assets [Abstract]	'	'
Derivative Asset, Fair Value, Gross Asset	$12.90	$8.50
Derivative Asset, Fair Value, Gross Amounts Offset	-6.5	-0.7
Derivative Assets, Fair Value, Net	6.4	7.8
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	6.4	7.8
Derivative Liabilities [Abstract]	'	'
Derivative Liability, Fair Value, Gross Liability	8.3	1
Derivative Liability, Fair Value, Gross Amounts Offset	-6.5	-0.9
Derivative Liabilities, Fair Value, Net	1.8	0.1
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	1.8	0.1
Kansas City Power and Light Company [Member]	'	'
Derivative Assets [Abstract]	'	'
Derivative Asset, Fair Value, Gross Asset	6.3	1.2
Derivative Asset, Fair Value, Gross Amounts Offset	-5.1	-0.1
Derivative Assets, Fair Value, Net	1.2	1.1
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	1.2	1.1
Derivative Liabilities [Abstract]	'	'
Derivative Liability, Fair Value, Gross Liability	5.1	0.3
Derivative Liability, Fair Value, Gross Amounts Offset	-5.1	-0.3
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

Derivative_Instruments_Fair_Va

Derivative Instruments Fair Value (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Derivatives, Fair Value [Line Items]	'	'
Derivative Asset, Fair Value, Gross Asset	$12.90	$8.50
Derivative Liability, Fair Value, Gross Liability	8.3	1
Kansas City Power and Light Company [Member]	'	'
Derivatives, Fair Value [Line Items]	'	'
Derivative Asset, Fair Value, Gross Asset	6.3	1.2
Derivative Liability, Fair Value, Gross Liability	5.1	0.3
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Balance Sheet Location [Member]	'	'
Derivatives, Fair Value [Line Items]	'	'
Derivative Asset, Fair Value, Gross Asset	12.9	8.5
Derivative Liability, Fair Value, Gross Liability	8.3	1
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Balance Sheet Location [Member] | Kansas City Power and Light Company [Member]	'	'
Derivatives, Fair Value [Line Items]	'	'
Derivative Asset, Fair Value, Gross Asset	6.3	1.2
Derivative Liability, Fair Value, Gross Liability	$5.10	$0.30

Derivative_Instruments_Gain_an

Derivative Instruments Gain and Losses (Details) (Not Designated as Hedging Instrument [Member], Commodity Contract [Member], USD $)	3 Months Ended		6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (losses) reflected in the income statement or regulatory account for changes in fair value of commodity contracts not designated as hedging	($7.50)	$0.70	($4.80)	($2.20)
Regulatory Asset [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of gain (loss) recognized in regulatory account for changes in fair value of commodity contracts not designated as hedging	-4	-0.7	-4.1	-1.6
Regulatory Liability [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of gain (loss) recognized in regulatory account for changes in fair value of commodity contracts not designated as hedging	-0.9	0	0.2	0
Kansas City Power and Light Company [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (losses) reflected in the income statement or regulatory account for changes in fair value of commodity contracts not designated as hedging	-5.2	1.6	-4.4	0.6
Kansas City Power and Light Company [Member] | Regulatory Asset [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of gain (loss) recognized in regulatory account for changes in fair value of commodity contracts not designated as hedging	-2.1	0	-2.2	0
Purchased Power Costs [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (losses) reflected in the income statement for changes in fair value of commodity contracts not designated as hedging	0	0	0.4	0
Fuel Costs [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (losses) reflected in the income statement for changes in fair value of commodity contracts not designated as hedging	0.6	1.4	1	-0.6
Fuel Costs [Member] | Kansas City Power and Light Company [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (losses) reflected in the income statement for changes in fair value of commodity contracts not designated as hedging	0.1	1.6	0.1	0.6
Electric Revenues [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (losses) reflected in the income statement for changes in fair value of commodity contracts not designated as hedging	-3.2	0	-2.3	0
Electric Revenues [Member] | Kansas City Power and Light Company [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (losses) reflected in the income statement for changes in fair value of commodity contracts not designated as hedging	($3.20)	$0	($2.30)	$0

Fair_Value_Measurements_Level_

Fair Value Measurements Level 3 (Details) (Fair Value, Inputs, Level 3 [Member], Fair Value, Measurements, Recurring [Member], USD $)	3 Months Ended		6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Net asset (liability) beginning of period	$6.90	$2.40	$3.30	$2.30
Purchases	7.3	0	13.4	0
Settlements	-10.3	-2.4	-21.2	-4.7
Net asset (liability) end of period	0.6	1.9	0.6	1.9
Purchased Power Costs [Member]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	'	'	0.4	0
Non-Operating Income [Member]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	4	1.9	11.1	4.3
Electric Revenues [Member]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	-3.2	0	-2.3	0
Derivative Financial Instruments, Assets [Member] | Non-Operating Income [Member]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	0.1	-0.3	0.2	-0.1
Derivative Financial Instruments, Assets [Member] | Electric Revenues [Member]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	-2.4	0	-2.5	0
Regulatory Asset [Member]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Regulatory Account	-4.1	0	-4.1	0
Regulatory Asset [Member] | Derivative Financial Instruments, Assets [Member]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	-4.1	0	-4.1	0
Kansas City Power and Light Company [Member]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Net asset (liability) beginning of period	3.9	'	1.1	'
Purchases	6.7	'	11.8	'
Settlements	-4.4	'	-7.5	'
Net asset (liability) end of period	0.9	'	0.9	'
Kansas City Power and Light Company [Member] | Electric Revenues [Member]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	-3.2	'	-2.3	'
Kansas City Power and Light Company [Member] | Derivative Financial Instruments, Assets [Member] | Electric Revenues [Member]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	-2.4	'	-2.5	'
Kansas City Power and Light Company [Member] | Regulatory Asset [Member]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Regulatory Account	-2.1	'	-2.2	'
Kansas City Power and Light Company [Member] | Regulatory Asset [Member] | Derivative Financial Instruments, Assets [Member]	'	'	'	'
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	($2.10)	'	($2.20)	'

Fair_Value_Measurements_Fair_V

Fair Value Measurements Fair Value Long-Term Debt (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Billions, unless otherwise specified
Carrying (Reported) Amount, Fair Value Disclosure [Member]	'	'
Fair value of financial instruments [Abstract]	'	'
Long-term Debt	$3.50	$3.50
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	2.3
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]	'	'
Fair value of financial instruments [Abstract]	'	'
Long-term debt fair value	3.9	3.7
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member] | Kansas City Power and Light Company [Member]	'	'
Fair value of financial instruments [Abstract]	'	'
Long-term debt fair value	$2.60	$2.50

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	Jun. 30, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Assets [Abstract]	'		'
Derivative instruments, assets	$6.40		$7.80
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	1.8		0.1
Kansas City Power and Light Company [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	1.2		1.1
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	0		0
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	6.4	[1]	7.8	[1]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	194.8	[2]	183.9	[2]
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	15.4	[3]	14.8	[3]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	18.1	[4]	18.7	[4]
Total assets	234.7		225.2
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	1.8	[1]	0.1	[1]
Total liabilities	1.8		0.1
Fair Value, Measurements, Recurring [Member] | Netting [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Cash collateral posted with third parties as part of netting agreements	'		0.2
Assets [Abstract]	'		'
Derivative instruments, assets	-6.5	[1],[5]	-0.7	[1],[5]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[2],[5]	0	[2],[5]
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	0	[3],[5]	0	[3],[5]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0	[4],[5]	0	[4],[5]
Total assets	-6.5	[5]	-0.7	[5]
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	-6.5		-0.9	[1],[5]
Total liabilities	-6.5	[5]	-0.9	[5]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	0.7		0.3	[1]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	159.7	[2]	152.7	[2]
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	7	[3]	4.8	[3]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0.1		0.1	[4]
Total assets	167.5		157.9
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	0.2		0.9	[1]
Total liabilities	0.2		0.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	3.5		4.9	[1]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	35.1	[2]	31.2	[2]
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	8.4	[3]	10	[3]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	18		18.6	[4]
Total assets	65		64.7
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	0		0.1	[1]
Total liabilities	0		0.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	8.7		3.3	[1]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[2]	0	[2]
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	0	[3]	0	[3]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0		0	[4]
Total assets	8.7		3.3
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	8.1		0	[1]
Total liabilities	8.1		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	1.2	[1]	1.1	[1]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	194.8		183.9
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	15.4		14.8
SERP rabbi trust [Abstract]	'		'
Total assets	211.4		199.8
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] | Equity Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	135		127.7
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	1.2		0.9
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Debt Securities [Member]	'		'
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	8.4		9.3
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | US Treasury and Government [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	21.3		21.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | US Government Corporations and Agencies Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	4.9		2.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | US States and Political Subdivisions Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	4		3.9
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Corporate Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	25.7		24.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Foreign Government Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0.6		0.5
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Cash Equivalents [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	3.4		3.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Other Assets [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	-0.1		-0.4
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	'		1.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Cash and Cash Equivalents [Member]	'		'
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	5.8		3.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	-5.1	[1],[5]	-0.1	[1],[5]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	0	[5]	0	[5]
SERP rabbi trust [Abstract]	'		'
Total assets	-5.1	[5]	-0.1	[5]
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	-5.1	[1],[5]	-0.3	[1],[5]
Total liabilities	-5.1	[5]	-0.3	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | Equity Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | Debt Securities [Member]	'		'
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | US Treasury and Government [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | US Government Corporations and Agencies Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | US States and Political Subdivisions Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | Corporate Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | Foreign Government Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | Cash Equivalents [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | Other Assets [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0	[5]	0	[5]
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	'		0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Netting [Member] | Cash and Cash Equivalents [Member]	'		'
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	0.3	[1]	0.1	[1]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	159.7		152.7
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	7		4.8
SERP rabbi trust [Abstract]	'		'
Total assets	167		157.6
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	0	[1]	0.3	[1]
Total liabilities	0		0.3
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	135		127.7
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	1.2		0.9
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Securities [Member]	'		'
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	0		0.5
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury and Government [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	21.3		21.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Corporations and Agencies Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | US States and Political Subdivisions Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Government Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	3.4		3.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Other Assets [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	'		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]	'		'
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	5.8		3.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	0	[1]	0	[1]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	35.1		31.2
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	8.4		10
SERP rabbi trust [Abstract]	'		'
Total assets	43.5		41.2
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	0	[1]	0	[1]
Total liabilities	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Securities [Member]	'		'
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	8.4		8.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Corporations and Agencies Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	4.9		2.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | US States and Political Subdivisions Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	4		3.9
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	25.7		24.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0.6		0.5
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Other Assets [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	-0.1		-0.4
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	'		1.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]	'		'
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	6	[1]	1.1	[1]
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	0		0
SERP rabbi trust [Abstract]	'		'
Total assets	6		1.1
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	5.1	[1]	0	[1]
Total liabilities	5.1		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member]	'		'
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury and Government [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Corporations and Agencies Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | US States and Political Subdivisions Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Government Debt Securities [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Cash Equivalents [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Other Assets [Member]	'		'
Nuclear decommissioning trust [Abstract]	'		'
Decommissioning Fund Investments, Fair Value	0		0
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	'		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]	'		'
Self-insured health plan trust [Abstract]	'		'
Self Insured Health Plan Trust Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Estimate of Fair Value Measurement [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	5.2	[1]	6.7	[1]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	18.1		18.7
Total assets	23.3		25.4
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	1.8	[1]	0.1	[1]
Total liabilities	1.8		0.1
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Estimate of Fair Value Measurement [Member] | Equity Securities [Member]	'		'
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0.1		0.1
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Estimate of Fair Value Measurement [Member] | Fixed Income Funds [Member]	'		'
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	18		18.6
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Netting [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	-1.4	[1],[5]	-0.6	[1],[5]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0	[5]	0	[5]
Total assets	-1.4	[5]	-0.6	[5]
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	-1.4	[1],[5]	-0.6	[1],[5]
Total liabilities	-1.4	[5]	-0.6	[5]
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Netting [Member] | Equity Securities [Member]	'		'
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Netting [Member] | Fixed Income Funds [Member]	'		'
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0	[5]	0	[5]
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 1 [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	0.4	[1]	0.2	[1]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0.1		0.1
Total assets	0.5		0.3
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	0.2	[1]	0.6	[1]
Total liabilities	0.2		0.6
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]	'		'
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0.1		0.1
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 1 [Member] | Fixed Income Funds [Member]	'		'
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 2 [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	3.5	[1]	4.9	[1]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	18		18.6
Total assets	21.5		23.5
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	0	[1]	0.1	[1]
Total liabilities	0		0.1
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]	'		'
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Income Funds [Member]	'		'
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	18		18.6
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 3 [Member]	'		'
Assets [Abstract]	'		'
Derivative instruments, assets	2.7	[1]	2.2	[1]
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0		0
Total assets	2.7		2.2
Liabilities [Abstract]	'		'
Derivative instruments, liabilities	3	[1]	0	[1]
Total liabilities	3		0
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]	'		'
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Income Funds [Member]	'		'
SERP rabbi trust [Abstract]	'		'
SERP Rabbi Trusts, Fair Value Disclosure	$0		$0
[1]	The fair value of derivative instruments is estimated using market quotes, over-the-counter forward price and volatility curves and correlations among fuel prices, net of estimated credit risk. Derivative instruments classified as Level 1 represent exchange traded derivative instruments. Derivative instruments classified as Level 2 represent non-exchange traded derivative instruments traded in over-the-counter markets. Derivative instruments classified as Level 3 represent non-exchange traded derivatives traded in over-the-counter markets for which observable market data is not available to corroborate the valuation inputs and TCRs valued at the most recent auction price in the SPP Integrated Marketplace.
[2]	Fair value is based on quoted market prices of the investments held by the fund and/or valuation models.
[3]	Fair value is based on quoted market prices of the investments held by the trust. Debt securities classified as Level 1 are comprised of U.S. Treasury securities. Debt securities classified as Level 2 are comprised of corporate bonds, U.S. Agency, state and local obligations, and other asset-backed securities.
[4]	Fair value is based on quoted market prices and/or valuation models for equity securities and Net Asset Value (NAV) per share for fixed income funds.
[5]	Represents the difference between derivative contracts in an asset or liability position presented on a net basis by counterparty on the consolidated balance sheets where a master netting agreement exists between the Company and the counterparty. At DecemberB 31, 2013, Great Plains Energy netted $0.2 million of cash collateral posted with counterparties.

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Income (Loss) (Details) (USD $)	3 Months Ended				6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]	'		'		'		'
Beginning balance	'		'		($25.30)	[1]	($38.40)	[1]
Amounts reclassified from accumulated other comprehensive loss	'		'		5.5	[1]	6.3	[1]
Net current period other comprehensive income	2.5		3.1		5.5	[1]	6.3	[1]
Ending balance	-19.8	[1]	-32.1	[1]	-19.8	[1]	-32.1	[1]
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'		'		'		'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'		'		'		'
Beginning balance	'		'		-23.8	[1]	-35.4	[1]
Amounts reclassified from accumulated other comprehensive loss	'		'		5.3	[1]	6.1	[1]
Net current period other comprehensive income	'		'		5.3	[1]	6.1	[1]
Ending balance	-18.5	[1]	-29.3	[1]	-18.5	[1]	-29.3	[1]
Accumulated Defined Benefit Plans Adjustment [Member]	'		'		'		'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'		'		'		'
Beginning balance	'		'		-1.5	[1]	-3	[1]
Amounts reclassified from accumulated other comprehensive loss	'		'		0.2	[1]	0.2	[1]
Net current period other comprehensive income	'		'		0.2	[1]	0.2	[1]
Ending balance	-1.3	[1]	-2.8	[1]	-1.3	[1]	-2.8	[1]
Kansas City Power and Light Company [Member]	'		'		'		'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'		'		'		'
Beginning balance	'		'		-20.2		'
Net current period other comprehensive income	1.4		1.3		2.7		2.8
Ending balance	-17.5		'		-17.5		'
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	'		'		-20.2	[1]	-25.8	[1]
Amounts reclassified from accumulated other comprehensive loss	'		'		2.7	[1]	2.8	[1]
Net current period other comprehensive income	'		'		2.7	[1]	2.8	[1]
Ending balance	($17.50)	[1]	($23)	[1]	($17.50)	[1]	($23)	[1]
[1]	Net of tax

Accumulated_Other_Comprehensiv3

Accumulated Other Comprehensive Income (Loss) Reclassification (Details) (USD $)	3 Months Ended		6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Interest charges	($48.30)	($49.40)	($97.70)	($99.10)
Fuel	-115.4	-121.2	-250.6	-253.4
Utility operating and maintenance expenses	-183.4	-166.4	-364.1	-321.6
Income before income tax (expense) benefit and income (loss) from equity investments	79	96.4	110.8	134
Income tax (expense) benefit	-27	-32.7	-35.1	-44.2
Reclassification out of Accumulated Other Comprehensive Income [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Net income (loss)	-2.5	-3.1	-5.5	-6.3
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	-3.9	-4.7	-8.6	-9.9
Income tax (expense) benefit	1.4	1.8	3.3	3.8
Net income (loss)	-2.5	-2.9	-5.3	-6.1
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	-3.9	-4.7	-8.6	-9.7
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	-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	-0.3	-0.3	-0.3
Income before income tax (expense) benefit and income (loss) from equity investments	-0.1	-0.3	-0.3	-0.3
Income tax (expense) benefit	0.1	0.1	0.1	0.1
Net income (loss)	0	-0.2	-0.2	-0.2
Kansas City Power and Light Company [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Interest charges	-31	-31.5	-61.7	-63.5
Fuel	-88.2	-86	-181.8	-180.5
Utility operating and maintenance expenses	-129.1	-116.7	-256.3	-224.9
Income before income tax (expense) benefit and income (loss) from equity investments	50.4	64.5	71.6	86.1
Income tax (expense) benefit	-15.6	-20.3	-19.6	-25.7
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	-2.2	-2.2	-4.4	-4.6
Income tax (expense) benefit	0.8	0.9	1.7	1.8
Net income (loss)	-1.4	-1.3	-2.7	-2.8
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	-2.2	-2.2	-4.4	-4.4
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	($0.20)

Income_Tax_Expense_Details

Income Tax Expense (Details) (USD $)	3 Months Ended		6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Current income taxes	'	'	'	'
Federal	($0.20)	$0	$0.10	$0
State	0	0.2	0.1	0.1
Current Income Tax Expense (Benefit), Total	-0.2	0.2	0.2	0.1
Deferred income taxes	'	'	'	'
Federal	25	27.6	31.6	37.5
State	5.1	5.7	6.8	8
Deferred Income Tax Expense (Benefit), Total	30.1	33.3	38.4	45.5
Noncurrent income taxes	'	'	'	'
Federal	-2.4	0	-2.4	0
State	-0.3	-0.2	-0.3	-0.2
Foreign	0.2	-0.2	0	-0.3
Noncurrent Income Tax Expense (Benefit), Total	-2.5	-0.4	-2.7	-0.5
Investment tax credit	'	'	'	'
Investment tax credit amortization	-0.4	-0.4	-0.8	-0.9
Total income tax expense	27	32.7	35.1	44.2
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)	-0.60%	-0.30%	-0.90%	0.20%
Amortization of investments tax credits (in hundredths)	-0.50%	-0.40%	-0.70%	-0.60%
Federal income tax credits (in hundredths)	-3.80%	-3.80%	-5.40%	-5.00%
State income taxes (in hundredths)	3.80%	3.80%	3.80%	3.90%
Changes in uncertain tax positions, net (in hundredths)	0.30%	-0.30%	0.00%	-0.40%
Effective Income Tax Rate Reconciliation, Other Adjustments	-0.20%	-0.10%	-0.30%	-0.10%
Effective Income Tax Rate Reconciliation, Percent	34.00%	33.90%	31.50%	33.00%
Kansas City Power and Light Company [Member]	'	'	'	'
Current income taxes	'	'	'	'
Federal	-2	-0.3	0.7	-0.6
State	-0.3	-0.1	0.2	-0.1
Current Income Tax Expense (Benefit), Total	-2.3	-0.4	0.9	-0.7
Deferred income taxes	'	'	'	'
Federal	14.9	16.6	15.3	20.6
State	3.3	3.7	3.9	5
Deferred Income Tax Expense (Benefit), Total	18.2	20.3	19.2	25.6
Noncurrent income taxes	'	'	'	'
Federal	0	0.6	0	1.1
State	0	0.1	0	0.2
Noncurrent Income Tax Expense (Benefit), Total	0	0.7	0	1.3
Investment tax credit	'	'	'	'
Investment tax credit amortization	-0.3	-0.3	-0.5	-0.5
Total income tax expense	$15.60	$20.30	$19.60	$25.70
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%	-1.80%	-0.10%
Amortization of investments tax credits (in hundredths)	-0.50%	-0.40%	-0.70%	-0.60%
Federal income tax credits (in hundredths)	-5.90%	-5.70%	-8.30%	-7.70%
State income taxes (in hundredths)	3.80%	3.80%	3.70%	3.80%
Changes in uncertain tax positions, net (in hundredths)	0.00%	-0.10%	0.00%	-0.10%
Effective Income Tax Rate Reconciliation, Other Adjustments	-0.50%	-0.30%	-0.60%	-0.40%
Effective Income Tax Rate Reconciliation, Percent	31.00%	31.60%	27.30%	29.90%

Taxes_Uncertain_Tax_Positions_

Taxes Uncertain Tax Positions (Details) (USD $)	6 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Uncertain Tax Positions [Line Items]	'	'
Amount expected to impact the effective tax rate if recognized	$6.50	$6.50
Accrued interest related to unrecognized tax benefits	3.4	3.2
Accrued penalties with respect to unrecognized tax benefits	0.6	0.6
Amount of unrecognized tax benefits that may be recognized in the next twelve months due to statute expirations or settlement agreements with tax authorities	6.1	'
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'	'
Balance at beginning of period	9.8	21.4
Reductions for current year tax positions	-0.2	-0.3
Reductions for prior year tax positions	-0.7	-10.5
Statute expirations	0	-0.3
Foreign currency translation adjustments	0	-0.5
Balance at end of period	$8.90	$9.80

Segments_and_Related_Informati2

Segments and Related Information (Details) (USD $)	3 Months Ended		6 Months Ended			12 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]	'	'	'		'	'
Operating revenues	$648.40	$600.30	$1,233.50		$1,142.50	'
Depreciation and amortization	-75.6	-72.6	-150.1		-142.8	'
Interest charges	-48.3	-49.4	-97.7		-99.1	'
Income tax (expense) benefit	-27	-32.7	-35.1		-44.2	'
Net income (loss) attributable to Great Plains Energy	52.1	63.6	75.9		89.6	'
Assets, Total	10,058.10	'	10,058.10		'	9,795.40
Capital expenditures	'	'	352.9	[1]	339.8	669	[1]
Electric Utility Segment [Member] | Electric Utility Segment [Member]	'	'	'		'	'
Segment Reporting Information [Line Items]	'	'	'		'	'
Operating revenues	648.4	600.3	1,233.50		1,142.50	'
Depreciation and amortization	-75.6	-72.6	-150.1		-142.8	'
Interest charges	-46	-47.4	-93		-95.2	'
Income tax (expense) benefit	-28	-33.9	-37.8		-46.5	'
Net income (loss) attributable to Great Plains Energy	54.7	65.5	80.8		93.1	'
Assets, Total	10,325.70	'	10,325.70		'	10,019.60
Capital expenditures	'	'	352.9	[1]	'	669	[1]
Other [Member]	'	'	'		'	'
Segment Reporting Information [Line Items]	'	'	'		'	'
Operating revenues	0	0	0		0	'
Depreciation and amortization	0	0	0		0	'
Interest charges	-11.7	-14.6	-24.3		-29.1	'
Income tax (expense) benefit	1	1.2	2.7		2.3	'
Net income (loss) attributable to Great Plains Energy	-2.6	-1.9	-4.9		-3.5	'
Assets, Total	120.8	'	120.8		'	105.6
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	9.4	12.6	19.6		25.2	'
Income tax (expense) benefit	0	0	0		0	'
Net income (loss) attributable to Great Plains Energy	0	0	0		0	'
Assets, Total	-388.4	'	-388.4		'	-329.8
Capital expenditures	'	'	$0	[1]	'	$0	[1]
[1]	Capital expenditures reflect year to date amounts for the periods presented.