Evergy Metro 10-K 25 Feb 15 2014 FY Annual report Financial data

Document_And_Entity_Informatio

Document And Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Feb. 24, 2015	Jun. 30, 2014
Entity information [Abstract]
Entity Registrant Name	Great Plains Energy Inc
Entity Central Index Key	1143068
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$4,136,403,349
Entity Common Stock, Shares Outstanding		154,196,171
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14

Consolidated_Statements_of_Inc

Consolidated Statements of Income and Comprehensive Income (USD $)	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Operating Revenues
Electric revenues	$2,568.20		$2,446.30		$2,309.90
Operating Expenses
Fuel	489.2		539.5		539.5
Purchased power	253.3		125.9		94
Transmission	74.7		53.2		35.4
Utility operating and maintenance expenses	701.9		671.4		647.3
Voluntary separation program	0		0		-4.3
Depreciation and amortization	306		289.7		272.3
General taxes	204.6		194.4		179.3
Other General and Administrative Expense	4		3		7.5
Costs and Expenses, Total	2,033.70		1,877.10		1,771
Operating Income (Loss)	534.5		569.2		538.9
Non-operating income	25		18.4		7.3
Non-operating expenses	-12.5		-9.6		-20.5
Interest charges	-188.5		-198.4		-220.8
Income before income tax (expense) benefit and income (loss) from equity investments	358.5		379.6		304.9
Income tax (expense) benefit	-115.7		-129.2		-104.6
(Income) loss from equity investments, net of income taxes	0		-0.2		-0.4
Net income (loss)	242.8		250.2		199.9
Preferred stock dividend requirements	1.6		1.6		1.6
Earnings (loss) available for common shareholders	241.2		248.6		198.3
Average number of common shares outstanding (in shares)	153.9		153.5		145.5
Average number of diluted common shares outstanding (in shares)	154.1		153.7		147.2
Basic earnings (loss) per common share
Earnings Per Share, Basic	$1.57		$1.62		$1.36
Diluted earnings (loss) per common share
Diluted earnings per share	$1.57		$1.62		$1.35
Comprehensive Income
Net income (loss)	242.8		250.2		199.9
Other comprehensive income
Gain (loss) on derivative hedging instruments	0		0		-0.1
Reclassification to expenses, net of tax	8		11.6		12.6
Derivative hedging activity, net of tax	8		11.6		12.5
Net gain (loss) arising during period	-3		2.1		-2.3
Income tax (expense) benefit	1.2		-0.9		0.9
Net gain (loss) arising during period, net of tax	-1.8		1.2		-1.4
Amortization of net losses included in net periodic benefit costs, net of tax	0.4		0.3		0.3
Change in unrecognized pension expense, net of tax	-1.4		1.5		-1.1
Total other comprehensive income (loss)	6.6	[1]	13.1	[1]	11.4
Comprehensive income (loss)	249.4		263.3		211.3
Common Stock, Dividends, Per Share, Declared	$0.94		$0.88		$0.86
Kansas City Power and Light Company [Member]
Operating Revenues
Electric revenues	1,730.80		1,671.40		1,579.90
Operating Expenses
Fuel	364.9		383		384.8
Purchased power	107.8		62.4		35.5
Transmission	47.2		37.3		24
Utility operating and maintenance expenses	489.1		475.9		460.1
Voluntary separation program	0		0		-4.3
Depreciation and amortization	213.9		198.3		185.6
General taxes	159.1		152		145.5
Other General and Administrative Expense	-1.3		0		0
Costs and Expenses, Total	1,380.70		1,308.90		1,231.20
Operating Income (Loss)	350.1		362.5		348.7
Non-operating income	20.4		16.3		4.4
Non-operating expenses	-8.3		-4.7		-8.6
Interest charges	-124.1		-125.3		-127.6
Income before income tax (expense) benefit and income (loss) from equity investments	238.1		248.8		216.9
Income tax (expense) benefit	-75.7		-79.8		-75.3
Net income (loss)	162.4		169		141.6
Comprehensive Income
Net income (loss)	162.4		169		141.6
Other comprehensive income
Gain (loss) on derivative hedging instruments	0		0		-0.1
Reclassification to expenses, net of tax	5.3		5.6		5.7
Derivative hedging activity, net of tax	5.3		5.6		5.6
Total other comprehensive income (loss)	5.3		5.6		5.6
Comprehensive income (loss)	$167.70		$174.60		$147.20
[1]	Net of tax

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Current Assets
Cash and cash equivalents	$13		$10.60
Funds on deposit	1.2		0.8
Receivables, net	160.3		162.2
Accounts receivable pledged as collateral	171		175
Fuel inventories, at average cost	90.1		76.4
Materials and supplies, at average cost	152.7		152.3
Deferred refueling outage costs	12.5		29.5
Refundable income taxes	3.1		10.5
Deferred income taxes	78.1		80.3
Assets held for sale	0		36.2
Prepaid expenses and other assets	36.9		33.2
Assets, Current, Total	718.9		767
Utility Plant, at Original Cost
Electric	12,128.70	[1]	11,575.30	[1]
Less-accumulated depreciation	4,828.30		4,628.40
Net utility plant in service	7,300.40		6,946.90
Construction work in progress	900		736.7
Nuclear Fuel, Net of Amortization	79.2		62.8
Public Utilities, Property, Plant and Equipment, Net	8,279.60		7,746.40
Investments and Other Assets
Nuclear decommissioning trust fund	199		183.9
Regulatory Assets	1,034.60		849.7
Goodwill	169		169
Other Assets, Noncurrent	74.6		79.4
Investments and Other Assets, Total	1,477.20		1,282
Assets, Total	10,475.70		9,795.40
Current Liabilities
Notes payable	4		9
Collateralized note payable	171		175
Commercial paper	358.3		108.2
Current maturities of long-term debt	15.1		1.1
Accounts payable	388		327.4
Accrued taxes	30.4		29.7
Accrued interest	41.3		45.4
Accrued compensation and benefits	35.2		47.3
Pension and post-retirement liability	2.8		3.2
Other Liabilities, Current	24.7		23.5
Liabilities, Current, Total	1,070.80		769.8
Deferred Credits and Other Liabilities
Deferred income taxes	1,089.70		964.8
Deferred tax credits	126		127.4
Asset retirement obligations	195.9		158.8
Pension and post-retirement liability	508.6		360.5
Regulatory liabilities	282.7		264
Other Liabilities, Noncurrent	88.9		121
Liabilities, Noncurrent, Total	2,291.80		1,996.50
Common shareholders' equity
Common Stock, Value, Issued	2,639.30		2,631.10
Retained earnings	967.8		871.4
Treasury Stock, Value	-2.3		-2.8
Accumulated other comprehensive loss	-18.7	[2]	-25.3	[2]
Common Shareholders' Equity, Total	3,586.10		3,474.40
Cumulative preferred stock $100 par value
Preferred Stock, Value, Issued	39		39
Long-term debt	3,488		3,515.70
Total Capitalization	7,113.10		7,029.10
Commitments and Contingencies
Liabilities and Equity, Total	10,475.70		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	2.7		4
Funds on deposit	0.6		0.7
Receivables, net	128.9		129.2
Related party receivables	68.8		50.4
Accounts receivable pledged as collateral	110		110
Fuel inventories, at average cost	58.8		50.3
Materials and supplies, at average cost	110.1		109
Deferred refueling outage costs	12.5		29.5
Refundable income taxes	57.5		15.1
Deferred income taxes	5		0
Assets held for sale	0		4.7
Prepaid expenses and other assets	32.7		27.5
Assets, Current, Total	587.6		530.4
Utility Plant, at Original Cost
Electric	8,737.30	[3]	8,274.90	[3]
Less-accumulated depreciation	3,658.70		3,518.30
Net utility plant in service	5,078.60		4,756.60
Construction work in progress	791.2		660.4
Nuclear Fuel, Net of Amortization	79.2		62.8
Public Utilities, Property, Plant and Equipment, Net	5,949		5,479.80
Investments and Other Assets
Nuclear decommissioning trust fund	199		183.9
Regulatory Assets	745.7		614.1
Other Assets, Noncurrent	29.5		31
Investments and Other Assets, Total	974.2		829
Assets, Total	7,510.80		6,839.20
Current Liabilities
Collateralized note payable	110		110
Commercial paper	358.3		93.2
Current maturities of long-term debt	14		0
Accounts payable	305.2		239.8
Related party payables	12.6		0.2
Accrued taxes	23.6		23.8
Accrued interest	29		29.1
Accrued compensation and benefits	35.2		47.3
Pension and post-retirement liability	1.5		1.9
Deferred income taxes	0		1.7
Other Liabilities, Current	12.4		13
Liabilities, Current, Total	901.8		560
Deferred Credits and Other Liabilities
Deferred income taxes	1,016.90		922.1
Deferred tax credits	124.3		125.3
Asset retirement obligations	177.7		141.7
Pension and post-retirement liability	485.4		339.9
Regulatory liabilities	172		168.3
Other Liabilities, Noncurrent	59.2		90.4
Liabilities, Noncurrent, Total	2,035.50		1,787.70
Common shareholders' equity
Common Stock, Value, Issued	1,563.10		1,563.10
Retained earnings	726.8		636.4
Accumulated other comprehensive loss	-14.9		-20.2
Common Shareholders' Equity, Total	2,275		2,179.30
Cumulative preferred stock $100 par value
Long-term debt	2,298.50		2,312.20
Total Capitalization	4,573.50		4,491.50
Commitments and Contingencies
Liabilities and Equity, Total	$7,510.80		$6,839.20
[1]	Includes $127.9 million and $107.8 million at December 31, 2014 and 2013, respectively, of land and other assets that are not depreciated.
[2]	Net of tax
[3]	Includes $72.4 million and $54.1 million at December 31, 2014 and 2013, respectively, of land and other assets that are not depreciated.

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Utility Plant, at Original Cost
Nuclear fuel, amortization	$187.50	$161.40
Common shareholder's equity
Common stock - shares authorized (in shares)	250,000,000	250,000,000
Common stock-shares issued (in shares)	154,254,037	153,995,621
Treasury stock- shares (in shares)	91,281	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	$187.50	$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_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash Flows from Operating Activities
Net income (loss)	$242.80	$250.20	$199.90
Adjustments to reconcile income to net cash from operating activities:
Depreciation and amortization	306	289.7	272.3
Amortization of:
Nuclear fuel	26.1	22.8	24.7
Other	46.1	57.5	36
Deferred income taxes, net	125.8	134	121.2
Investment tax credit amortization	-1.4	-1.7	-2.4
(Income) loss from equity investments, net of income taxes	0	0.2	0.4
Other operating activities	-47.2	24.1	11.7
Net cash from operating activities	698.2	776.8	663.8
Cash Flows from Investing Activities
Utility capital expenditures	-773.7	-669	-610.2
Allowance for borrowed funds used during construction	-13	-11.8	-5.3
Purchases of nuclear decommissioning trust investments	-27.5	-73.5	-24.2
Proceeds from nuclear decommissioning trust investments	24.2	70.2	20.9
Proceeds from sale of transmission assets	37.7	0	0
Other investing activities	-27.5	-21.7	-19.6
Net cash from investing activities	-779.8	-705.8	-638.4
Cash Flows from Financing Activities
Issuance of common stock	4.8	4.9	293
Issuance of long-term debt	0	762.5	0
Issuance fees	-0.9	-9	-2.9
Repayment of long-term debt	-13.4	-265.3	-513.8
Net change in short-term borrowings	245.1	-424.9	253.1
Net change in collateralized short-term borrowings	-4	1	79
Dividends paid	-145.6	-137.3	-125.5
Other financing activities	-2	-1.6	-5.2
Net cash from financing activities	84	-69.7	-22.3
Net Change in Cash and Cash Equivalents	2.4	1.3	3.1
Cash and Cash Equivalents at Beginning of Year	10.6	9.3	6.2
Cash and Cash Equivalents at End of Year	13	10.6	9.3
Kansas City Power and Light Company [Member]
Cash Flows from Operating Activities
Net income (loss)	162.4	169	141.6
Adjustments to reconcile income to net cash from operating activities:
Depreciation and amortization	213.9	198.3	185.6
Amortization of:
Nuclear fuel	26.1	22.8	24.7
Other	29.3	34.3	30.1
Deferred income taxes, net	88.4	92.1	60.2
Investment tax credit amortization	-1	-1.1	-1.8
Other operating activities	-64.7	-9.2	27.9
Net cash from operating activities	454.4	506.2	468.3
Cash Flows from Investing Activities
Utility capital expenditures	-635.9	-521.9	-482
Allowance for borrowed funds used during construction	-11.1	-10.6	-3.7
Purchases of nuclear decommissioning trust investments	-27.5	-73.5	-24.2
Proceeds from nuclear decommissioning trust investments	24.2	70.2	20.9
Proceeds from sale of transmission assets	4.7	0	0
Other investing activities	-15.2	-12.4	-11.7
Net cash from investing activities	-660.8	-548.2	-500.7
Cash Flows from Financing Activities
Issuance of long-term debt	0	412.5	0
Issuance fees	-0.4	-5.7	0
Repayment of long-term debt	0	-2.6	-12.7
Net change in short-term borrowings	265.1	-267.8	134
Net change in collateralized short-term borrowings	0	0	15
Net money pool borrowings	12.4	-3.6	-4.7
Dividends paid	-72	-92	-96
Other financing activities	0	0	0.1
Net cash from financing activities	205.1	40.8	35.7
Net Change in Cash and Cash Equivalents	-1.3	-1.2	3.3
Cash and Cash Equivalents at Beginning of Year	4	5.2	1.9
Cash and Cash Equivalents at End of Year	$2.70	$4	$5.20

Consolidated_Statements_of_Com

Consolidated Statements of Common Shareholders' Equity (USD $)	Total	Kansas City Power and Light Company [Member]	Parent 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, 2011				$2,330.60	$1,563.10	$684.70	$513.80	($5.60)	($49.80)	($31.40)
Beginning balance, treasury stock (in shares) at Dec. 31, 2011								-264,567
Beginning balance (in shares) at Dec. 31, 2011				136,406,306	1
Issuance of common stock				293
Issuance of common stock (in shares)				17,373,500
Equity compensation expense, net of forfeitures				0.3
Unearned Compensation [Abstract]
Issuance of restricted common stock				-3.3
Forfeiture of restricted common stock				1.3
Compensation expense recognized				2.3
Stockholders' Equity, Other				0.5
Net income (loss)	199.9	141.6				199.9	141.6
Loss on reissuance of treasury stock						-0.2
Dividends:
Common stock						-123.9	-96
Preferred stock - at required rates						-1.6
Performance shares						-0.1
Treasury shares acquired								-3.3
Treasury shares acquired (in shares)								-164,454
Treasury shares reissued								3.8
Treasury shares reissued (in shares)								178,785
Derivative hedging activity, net of tax	12.5	5.6	6.9						12.5	5.6
Change in unrecognized pension expense, net of tax	-1.1								-1.1
Ending balance at Dec. 31, 2012	3,340	2,096.70		2,624.70	1,563.10	758.8	559.4	-5.1	-38.4	-25.8
Ending balance (in shares) at Dec. 31, 2012				153,779,806	1
Ending balance, treasury stock (in shares) at Dec. 31, 2012								-250,236
Issuance of common stock				4.9
Issuance of common stock (in shares)				215,815
Equity compensation expense, net of forfeitures				0.4
Unearned Compensation [Abstract]
Issuance of restricted common stock				-1.8
Forfeiture of restricted common stock				0.1
Compensation expense recognized				2.1
Stockholders' Equity, Other				0.7
Net income (loss)	250.2	169				250.2	169
Loss on reissuance of treasury stock						0
Dividends:
Common stock						-135.7	-92
Preferred stock - at required rates						-1.6
Performance shares						-0.3
Treasury shares acquired								-1.6
Treasury shares acquired (in shares)								-73,201
Treasury shares reissued								3.9
Treasury shares reissued (in shares)								194,147
Derivative hedging activity, net of tax	11.6	5.6	6						11.6	5.6
Change in unrecognized pension expense, net of tax	1.5								1.5
Ending balance at Dec. 31, 2013	3,474.40	2,179.30	3,474.40	2,631.10	1,563.10	871.4	636.4	-2.8	-25.3	-20.2
Ending balance (in shares) at Dec. 31, 2013				153,995,621	1
Ending balance, treasury stock (in shares) at Dec. 31, 2013	-129,290		-129,290					-129,290
Issuance of common stock				6.7
Issuance of common stock (in shares)				258,416
Equity compensation expense, net of forfeitures				0.5
Unearned Compensation [Abstract]
Issuance of restricted common stock				-2.1
Forfeiture of restricted common stock				0
Compensation expense recognized				2
Stockholders' Equity, Other				1.1
Net income (loss)	242.8	162.4				242.8	162.4
Loss on reissuance of treasury stock						0
Dividends:
Common stock						-144	-72
Preferred stock - at required rates						-1.6
Performance shares						-0.8
Treasury shares acquired								-2.2
Treasury shares acquired (in shares)								-85,744
Treasury shares reissued								2.7
Treasury shares reissued (in shares)								123,753
Derivative hedging activity, net of tax	8	5.3	2.7						8	5.3
Change in unrecognized pension expense, net of tax	-1.4								-1.4
Ending balance at Dec. 31, 2014	$3,586.10	$2,275	$3,586.10	$2,639.30	$1,563.10	$967.80	$726.80	($2.30)	($18.70)	($14.90)
Ending balance (in shares) at Dec. 31, 2014				154,254,037	1
Ending balance, treasury stock (in shares) at Dec. 31, 2014	-91,281		-91,281					-91,281

Consolidated_Statements_of_Com1

Consolidated Statements of Common Shareholders' Equity (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock Transactions, Parenthetical Disclosures [Abstract]
Common Stock, Dividends, Per Share, Declared	$0.94	$0.88	$0.86

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 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 23 for additional information.
	Use of Estimates
	The process of preparing financial statements in conformity with Generally Accepted Accounting Principles (GAAP) requires the use of estimates and assumptions that affect the reported amounts of certain types of assets, liabilities, revenues and expenses. Such estimates primarily relate to unsettled transactions and events as of the date of the financial statements. Accordingly, upon settlement, actual results may differ from estimated amounts.
	Cash and Cash Equivalents
	Cash equivalents consist of highly liquid investments with original maturities of three months or less at acquisition.
	Funds on Deposit
	Funds on deposit consist primarily of cash provided to counterparties in support of margin requirements related to commodity purchases, commodity swaps and futures contracts. Pursuant to individual contract terms with counterparties, deposit amounts required vary with changes in market prices, credit provisions and various other factors. Interest is earned on most funds on deposit. Great Plains Energy also holds funds on deposit from counterparties in the same manner. These funds are included in other current liabilities on the consolidated balance sheets.
	Fair Value of Financial Instruments
	The following methods and assumptions were used to estimate the fair value of each class of financial instrument for which it is practicable to estimate that value.
	Nuclear decommissioning trust fund - KCP&L's nuclear decommissioning trust fund assets are recorded at fair value based on quoted market prices of the investments held by the fund and/or valuation models.
	Derivative instruments - The fair value of derivative instruments is estimated using market quotes, over-the-counter forward price and volatility curves and correlation among fuel prices, net of estimated credit risk.
	Pension plans - For financial reporting purposes, the market value of plan assets is the fair value. For regulatory reporting purposes, a five-year smoothing of assets is used to determine fair value.
	Derivative Instruments
	The Company records derivative instruments on the balance sheet at fair value in accordance with GAAP. Great Plains Energy and KCP&L enter into derivative contracts to manage exposure to commodity price and interest rate fluctuations. Derivative instruments are used solely for hedging purposes and are not issued or held for speculative reasons.
	The Company considers various qualitative factors, such as contract and market place attributes, in designating derivative instruments at inception. Great Plains Energy and KCP&L may elect the normal purchases and normal sales (NPNS) exception, which requires the effects of the derivative to be recorded when the underlying contract settles. Great Plains Energy and KCP&L account for derivative instruments that are not designated as NPNS as cash flow hedges or non-hedging derivatives, which are recorded as assets or liabilities on the consolidated balance sheets at fair value. In addition, if a derivative instrument is designated as a cash flow hedge, Great Plains Energy and KCP&L document the method of determining hedge effectiveness and measuring ineffectiveness. See Note 19 for additional information regarding derivative financial instruments and hedging activities.
	Great Plains Energy and KCP&L offset fair value amounts recognized for derivative instruments under master netting arrangements, which include rights to reclaim cash collateral (a receivable), or the obligation to return cash collateral (a payable). Great Plains Energy and KCP&L classify cash flows from derivative instruments accounted for as a cash flow hedge in the same category as the cash flows from the items being hedged.
	Utility Plant
	Great Plains Energy's and KCP&L's utility plant is stated at historical cost. These costs include taxes, an allowance for the cost of borrowed and equity funds used to finance construction and payroll-related costs, including pensions and other fringe benefits. Replacements, improvements and additions to units of property are capitalized. Repairs of property and replacements of items not considered to be units of property are expensed as incurred (except as discussed under Deferred Refueling Outage Costs). When property units are retired or otherwise disposed, the original cost, net of salvage, is charged to accumulated depreciation. Substantially all of KCP&L's utility plant is pledged as collateral for KCP&L's mortgage bonds under the General Mortgage Indenture and Deed of Trust dated December 1, 1986, as supplemented. Substantially all of GMO's St. Joseph Light & Power division utility plant is pledged as collateral for GMO's mortgage bonds under the General Mortgage Indenture and Deed of Trust dated April 1, 1946, as supplemented.
	As prescribed by The Federal Energy Regulatory Commission (FERC), Allowance for Funds Used During Construction (AFUDC) is charged to the cost of the plant during construction. AFUDC equity funds are included as a non-cash item in non-operating income and AFUDC borrowed funds are a reduction of interest charges. The rates used to compute gross AFUDC are compounded semi-annually and averaged 5.7% in 2014, 6.1% in 2013 and 2.0% in 2012 for KCP&L. The rates used to compute gross AFUDC for GMO averaged 6.1% in 2014, 2.1% in 2013 and 2.4% in 2012.
	Great Plains Energy's and KCP&L's balances of utility plant, at original cost, with a range of estimated useful lives are listed in the following tables.
	Great Plains Energy
	December 31		2014				2013
	Utility plant, at original cost		(millions)
	Generation (20 - 60 years)		$	7,169.60			$	6,874.60
	Transmission (15 - 70 years)		821.9				794
	Distribution (8 - 66 years)		3,311.60				3,149.40
	General (5 - 50 years)		825.6				757.3
	Total (a)		$	12,128.70			$	11,575.30
	(a) Includes $127.9 million and $107.8 million at December 31, 2014 and 2013, respectively, of land and other assets that are not depreciated.
	KCP&L
	December 31		2014				2013
	Utility plant, at original cost		(millions)
	Generation (20 - 60 years)		$	5,554.30			$	5,288.30
	Transmission (15 - 70 years)		448.9				433.7
	Distribution (8 - 55 years)		2,089.00				1,970.20
	General (5 - 50 years)		645.1				582.7
	Total (a)		$	8,737.30			$	8,274.90
	(a) Includes $72.4 million and $54.1 million at December 31, 2014 and 2013, respectively, of land and other assets that are not depreciated.
	Depreciation and Amortization
	Depreciation and amortization of utility plant other than nuclear fuel is computed using the straight-line method over the estimated lives of depreciable property based on rates approved by state regulatory authorities. Annual depreciation rates average approximately 3%. Nuclear fuel is amortized to fuel expense based on the quantity of heat produced during the generation of electricity.
	Great Plains Energy's depreciation expense was $277.9 million, $265.4 million and $251.4 million for 2014, 2013 and 2012, respectively. KCP&L's depreciation expense was $189.7 million, $179.2 million and $168.0 million for 2014, 2013 and 2012, respectively.
	Nuclear Plant Decommissioning Costs
	Nuclear plant decommissioning cost estimates are based on the immediate dismantlement method and include the costs of decontamination, dismantlement and site restoration. Based on these cost estimates, KCP&L contributes to a tax-qualified trust fund to be used to decommission Wolf Creek Generating Station (Wolf Creek). Related liabilities for decommissioning are included on Great Plains Energy's and KCP&L's balance sheets in Asset Retirement Obligations (AROs).
	As a result of the authorized regulatory treatment and related regulatory accounting, differences between the decommissioning trust fund asset and the related ARO are recorded as a regulatory asset or liability. See Note 7 for discussion of AROs including those associated with nuclear plant decommissioning costs.
	Deferred Refueling Outage Costs
	KCP&L uses the deferral method to account for operations and maintenance expenses incurred in support of Wolf Creek's scheduled refueling outages and amortizes them evenly (monthly) over the unit's operating cycle, which is approximately 18 months, until the next scheduled outage. Replacement power costs during an outage are expensed as incurred.
	Regulatory Matters
	KCP&L and GMO defer items on the balance sheet resulting from the effects of the ratemaking process, which would not be recorded if KCP&L and GMO were not regulated. See Note 5 for additional information concerning regulatory matters.
	Revenue Recognition
	Great Plains Energy and KCP&L recognize revenues on sales of electricity when the service is provided. Revenues recorded include electric services provided but not yet billed by KCP&L and GMO. Unbilled revenues are recorded for kWh usage in the period following the customers' billing cycle to the end of the month. KCP&L's and GMO's estimate is based on net system kWh usage less actual billed kWhs. KCP&L's and GMO's estimated unbilled kWhs are allocated and priced by regulatory jurisdiction across the rate classes based on actual billing rates.
	KCP&L and GMO collect from customers gross receipts taxes levied by state and local governments. These taxes from KCP&L's Missouri customers are recorded gross in operating revenues and general taxes on Great Plains Energy's and KCP&L's statements of income. KCP&L's gross receipts taxes collected from Missouri customers were $60.4 million, $58.9 million and $55.8 million in 2014, 2013 and 2012, respectively. These taxes from KCP&L's Kansas customers and GMO's customers are recorded net in operating revenues on Great Plains Energy's and KCP&L's statements of income.
	Great Plains Energy and KCP&L collect sales taxes from customers and remit to state and local governments. These taxes are presented on a net basis on Great Plains Energy's and KCP&L's statements of income.
	Great Plains Energy and KCP&L record sale and purchase activity on a net basis in wholesale revenue or purchased power when transacting with Regional Transmission Organization (RTO)/Independent System Operator (ISO) markets.
	Allowance for Doubtful Accounts
	This reserve represents estimated uncollectible accounts receivable and is based on management's judgment considering historical loss experience and the characteristics of existing accounts. Provisions for losses on receivables are expensed to maintain the allowance at a level considered adequate to cover expected losses. Receivables are charged off against the reserve when they are deemed uncollectible.
	Property Gains and Losses
	Net gains and losses from the sale of assets and businesses and from asset impairments are recorded in operating expenses.
Asset Impairments
Long-lived assets and finite-lived intangible assets subject to amortization are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. If the sum of the undiscounted expected future cash flows from an asset to be held and used is less than the carrying value of the asset, an asset impairment must be recognized in the financial statements. The amount of impairment recognized is the excess of the carrying value of the asset over its fair value.
Goodwill and indefinite lived intangible assets are tested for impairment annually and when an event occurs indicating the possibility that an impairment exists. The annual test must be performed at the same time each year. If the fair value of a reporting unit is less than its carrying value including goodwill, an impairment charge for goodwill must be recognized in the financial statements. To measure the amount of the impairment loss to recognize, the implied fair value of the reporting unit goodwill is compared with its carrying value.
Income Taxes
Income taxes are accounted for using the asset/liability approach. Deferred tax assets and liabilities are determined based on the temporary differences between the financial reporting and tax bases of assets and liabilities, applying enacted statutory tax rates in effect for the year in which the differences are expected to reverse. Deferred tax assets are reduced by a valuation allowance when, in the opinion of management, it is more likely than not that some portion of the deferred tax assets will not be realized.
Great Plains Energy and KCP&L recognize tax benefits based on a “more-likely-than-not” recognition threshold. In addition, Great Plains Energy and KCP&L recognize interest accrued related to unrecognized tax benefits in interest expense and penalties in non-operating expenses.
Great Plains Energy files a consolidated federal income tax return as well as unitary and combined income tax returns in several state jurisdictions with Kansas and Missouri being the most significant. Income taxes for consolidated or combined subsidiaries are allocated to the subsidiaries based on separate company computations of income or loss. KCP&L's income tax provision includes taxes allocated based on its separate company income or loss.
Great Plains Energy and KCP&L have established a net regulatory asset for the additional future revenues to be collected from customers for deferred income taxes. Tax credits are recognized in the year generated except for certain KCP&L and GMO investment tax credits that have been deferred and amortized over the remaining service lives of the related properties.
Environmental Matters
Environmental costs are accrued when it is probable a liability has been incurred and the amount of the liability can be reasonably estimated.
Basic and Diluted Earnings per Common Share Calculation
To determine basic earnings per common share (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, restricted stock and Equity Units. Great Plains Energy settled the Equity Units in June 2012.
The following table reconciles Great Plains Energy's basic and diluted EPS.
	2014				2013			2012
Income	(millions, except per share amounts)
Net income	$	242.8			$	250.2		$	199.9
Less: preferred stock dividend requirements	1.6				1.6			1.6
Earnings available for common shareholders	$	241.2			$	248.6		$	198.3
Common Shares Outstanding
Average number of common shares outstanding	153.9				153.5			145.5
Add: effect of dilutive securities	0.2				0.2			1.7
Diluted average number of common shares outstanding	154.1				153.7			147.2
Basic EPS	$	1.57			$	1.62		$	1.36
Diluted EPS	$	1.57			$	1.62		$	1.35
Anti-dilutive shares excluded from the computation of diluted EPS are detailed in the following table.
	2014			2013			2012
Performance shares	482,987			548,242			—
Restricted stock shares	3,287			2,228			3,781
Dividends Declared
In February 2015, Great Plains Energy's Board of Directors (Board) declared a quarterly dividend of $0.245 per share on Great Plains Energy's common stock.  The common dividend is payable March 20, 2015, to shareholders of record as of February 27, 2015.  The Board also declared regular dividends on Great Plains Energy's preferred stock, payable June 1, 2015, to shareholders of record as of May 8, 2015.
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 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	12 Months Ended
	Dec. 31, 2014
Supplemental Cash Flow Elements [Abstract]
Cash Flow, Supplemental Disclosures [Text Block]	2. SUPPLEMENTAL CASH FLOW INFORMATION
	Great Plains Energy Other Operating Activities
	Year Ended December 31	2014			2013			2012
	Cash flows affected by changes in:	(millions)
	Receivables	$	3		$	(7.1	)	$	76.8
	Accounts receivable pledged as collateral	4			(1.0		)	(79.0		)
	Fuel inventories	(13.7		)	18.7			(6.1		)
	Materials and supplies	(0.4		)	(1.0		)	(11.0		)
	Accounts payable	15.2			26.4			57.3
	Accrued taxes	8.3			2.2			(7.8		)
	Accrued interest	(4.1		)	3.9			(35.2		)
	Deferred refueling outage costs	17			(17.6		)	15.6
	Pension and post-retirement benefit obligations	25.5			31.3			14.4
	Allowance for equity funds used during construction	(18.0		)	(14.1		)	(1.3		)
	Fuel recovery mechanism	(28.5		)	(1.3		)	22.5
	Solar rebates paid	(43.2		)	(32.5		)	(15.9		)
	Uncertain tax positions	(9.0		)	(0.8		)	(4.7		)
	Other	(3.3		)	17			(13.9		)
	Total other operating activities	$	(47.2	)	$	24.1		$	11.7
	Cash paid during the period:
	Interest	$	174.8		$	170.8		$	247.9
	Income taxes	$	—		$	—		$	3.3
	Non-cash investing activities:
	Liabilities accrued for capital expenditures	$	57.4		$	48.1		$	57.5
	KCP&L Other Operating Activities
	Year Ended December 31	2014			2013			2012
	Cash flows affected by changes in:	(millions)
	Receivables	$	(18.1	)	$	(12.6	)	$	8.8
	Accounts receivable pledged as collateral	—			—			(15.0		)
	Fuel inventories	(8.5		)	13.3			(4.6		)
	Materials and supplies	(1.1		)	1.1			(9.0		)
	Accounts payable	20.4			7.3			48.3
	Accrued taxes	(42.5		)	(3.7		)	(2.0		)
	Accrued interest	(0.1		)	1.4			(2.3		)
	Deferred refueling outage costs	17			(17.6		)	15.6
	Pension and post-retirement benefit obligations	26.9			35.7			18
	Allowance for equity funds used during construction	(16.0		)	(14.1		)	(1.3		)
	Fuel recovery mechanism	(2.2		)	(1.8		)	5.1
	Solar rebates paid	(17.3		)	(8.2		)	(5.8		)
	Uncertain tax positions	—			(10.5		)	1.8
	Other	(23.2		)	0.5			(29.7		)
	Total other operating activities	$	(64.7	)	$	(9.2	)	$	27.9
	Cash paid during the period:
	Interest	$	112.1		$	111.7		$	118
	Income taxes	$	30.2		$	4.6		$	18
	Non-cash investing activities:
	Liabilities accrued for capital expenditures	$	48.8		$	40.5		$	48.4

Receivables

Receivables	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Receivables [Text Block]	3. RECEIVABLES
	Great Plains Energy's and KCP&L's receivables are detailed in the following table.
		December 31
		2014				2013
	Great Plains Energy	(millions)
	Customer accounts receivable - billed	$	1.1			$	1.5
	Customer accounts receivable - unbilled	75.3				74.6
	Allowance for doubtful accounts - customer accounts receivable	(2.8		)		(2.5		)
	Other receivables	86.7				88.6
	Total	$	160.3			$	162.2
	KCP&L
	Customer accounts receivable - billed	$	0.6			$	1.3
	Customer accounts receivable - unbilled	49.7				51.2
	Allowance for doubtful accounts - customer accounts receivable	(1.2		)		(1.1		)
	Other receivables	79.8				77.8
	Total	$	128.9			$	129.2
	Great Plains Energy's and KCP&L's other receivables at December 31, 2014 and 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 December 31, 2014 and 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 December 31, 2014 and 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 2015 and allows for $110 million in aggregate outstanding principal amount at any time.  GMO's agreement expires in September 2015 and allows for $65 million in aggregate outstanding principal from mid-November 2014 through mid-June 2015 and then increases to $80 million through September 2015.
	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.
	2014	KCP&L						KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
								Receivables				KCP&L								Receivables
								Company												Company
		(millions)
	Receivables (sold) purchased		$	(1,595.8	)				$	1,595.80			$	—			$	(816.3	)		$	816.3			$	—
	Gain (loss) on sale of accounts receivable (a)		(20.2		)				20.2				—				(10.3		)		10.4				0.1
	Servicing fees received (paid)		2.6						(2.6		)		—				1.2				(1.2		)		—
	Fees paid to outside investor		—						(1.1		)		(1.1		)		—				(0.6		)		(1.7		)
	Cash from customers (transferred) received		(1,608.3		)				1,608.30				—				(823.5		)		823.5				—
	Cash received from (paid for) receivables purchased		1,588.10						(1,588.1		)		—				813.1				(813.1		)		—
	Interest on intercompany note received (paid)		0.3						(0.3		)		—				0.1				(0.1		)		—
	2013	KCP&L						KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
								Receivables				KCP&L								Receivables
								Company												Company
		(millions)
	Receivables (sold) purchased		$	(1,517.2	)				$	1,517.20			$	—			$	(834.7	)		$	834.7			$	—
	Gain (loss) on sale of accounts receivable (a)		(19.2		)				19.1				(0.1		)		(10.6		)		10.5				(0.2		)
	Servicing fees received (paid)		2.6						(2.6		)		—				1.4				(1.4		)		—
	Fees paid to outside investor		—						(1.2		)		(1.2		)		—				(0.7		)		(1.9		)
	Cash from customers (transferred) received		(1,516.2		)				1,516.20				—				(830.9		)		830.9				—
	Cash received from (paid for) receivables purchased		1,497.20						(1,497.2		)		—				820.5				(820.5		)		—
	Interest on intercompany note received (paid)		0.3						(0.3		)		—				0.1				(0.1		)		—
	(a) Any net gain (loss) is the result of the timing difference inherent in collecting receivables and over the life of the agreement will net to zero.

Nuclear_Plant

Nuclear Plant	12 Months Ended
	Dec. 31, 2014
Nuclear Plant [Abstract]
Nuclear Plant	4. NUCLEAR PLANT
	KCP&L owns 47% of 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 were 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, which became effective May 16, 2014.
	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 Plant Decommissioning Costs
	The Public Service Commission of the State of Missouri (MPSC) and The State Corporation Commission of the State of Kansas (KCC) require KCP&L and the other owners of Wolf Creek to submit an updated decommissioning cost study every three years and to propose funding levels. The most recent study was submitted to the MPSC and KCC in August 2014 and is the basis for the current cost of decommissioning estimates in the following table. Funding levels included in KCP&L retail rates have not changed.
			KCC			MPSC
		(millions)
	Current cost of decommissioning (in 2014 dollars)
	Total Station		$	765.1		$	765.1
	KCP&L's 47% Share		359.6			359.6
	Future cost of decommissioning (in 2045-2053 dollars) (a)
	Total Station		$	2,201.50		$	2,253.10
	KCP&L's 47% Share		1,034.70			1,059.00
	Annual escalation factor		3.15%			3.22%
	Annual return on trust assets (b)		6.15%			5.68%
	(a) Total future cost over an eight year decommissioning period
	(b) The 6.15% and 5.68% rate of return for KCC and MPSC, respectively, is through 2025. The rates then systematically decrease through 2053 to 0.72% and 2.22% for KCC and MPSC, respectively, based on the assumption that the fund's investment mix will become increasingly conservative as the decommissioning period approaches.
	See Note 7 for information regarding the asset retirement obligation to decommission Wolf Creek.
	Nuclear Decommissioning Trust Fund
	In 2014 and 2013, KCP&L contributed approximately $3.3 million to a tax-qualified trust fund to be used to
	decommission Wolf Creek. Amounts funded are charged to other operating expense and recovered in customers'
	rates. The funding level assumes a projected level of return on trust assets. If the actual return on trust assets is
	below the projected level or actual decommissioning costs are higher than estimated, KCP&L could be responsible
	for the balance of funds required; however, while there can be no assurances, management believes a rate increase
	would be allowed to recover decommissioning costs over the remaining life of the unit.
	The following table summarizes the change in Great Plains Energy's and KCP&L's nuclear decommissioning trust fund.
		2014					2013
	Decommissioning Trust		(millions)
	Beginning balance January 1		$	183.9				$	154.7
	Contributions		3.3					3.3
	Earned income, net of fees		3.6					2.7
	Net realized gains		0.4					1.7
	Net unrealized gains		7.8					21.5
	Ending balance December 31		$	199				$	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.
		December 31
		2014																	2013
		Cost			Unrealized Gains						Unrealized				Fair			Cost			Unrealized			Unrealized				Fair
		Basis									Losses				Value			Basis			Gains			Losses				Value
		(millions)
	Equity securities	$	87.2			$	50.6					$	(0.7	)		$	137.1		$	83.7		$	44.6		$	(0.6	)		$	127.7
	Debt securities	55.4				3.8						(0.1		)		59.1			51			2.5			(0.7		)		52.8
	Other	2.8				—						—				2.8			3.4			—			—				3.4
	Total	$	145.4			$	54.4					$	(0.8	)		$	199		$	138.1		$	47.1		$	(1.3	)		$	183.9
	The weighted average maturity of debt securities held by the trust at December 31, 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.
		2014			2013				2012
		(millions)
	Realized gains	$	1.4		$	2.4			$	1.7
	Realized losses	(1.0		)	(0.7		)		(0.7		)
	Nuclear Insurance
	The owners of Wolf Creek (Owners) maintain nuclear insurance for Wolf Creek for nuclear liability, nuclear property and accidental outage. These policies contain certain industry standard exclusions, including, but not limited to, ordinary wear and tear, and war. The nuclear property insurance programs subscribed to by members of the nuclear power generating industry include industry aggregate limits for acts of terrorism and related losses, including replacement power costs. There is no industry aggregate limit for liability claims related to terrorism, regardless of the number of acts of terrorism affecting Wolf Creek or any other nuclear energy liability policy or the number of policies in place. An industry aggregate limit of $3.2 billion plus any reinsurance recoverable by Nuclear Electric Insurance Limited (NEIL), the Owners' insurance provider, exists for property claims related to nuclear acts of terrorism, including accidental outage power costs for nuclear acts of terrorism affecting Wolf Creek or any other nuclear energy facility property policy within twelve months from the date of the first act. An industry aggregate limit of $1.8 billion exists for property claims related to non-nuclear acts of terrorism. These limits plus any recoverable reinsurance are the maximum amount to be paid to members who sustain losses or damages from these types of terrorist acts. In addition, industry-wide retrospective assessment programs (discussed below) can apply once these insurance programs have been exhausted.
	In the event of a catastrophic loss at Wolf Creek, the insurance coverage may not be adequate to cover property damage and extra expenses incurred. Uninsured losses, to the extent not recovered through rates, would be assumed by KCP&L and the other owners and could have a material effect on Great Plains Energy's and KCP&L's results of operations, financial position and cash flows.
	Nuclear Liability Insurance
	Pursuant to the Price-Anderson Act, which was reauthorized through December 31, 2025, by the Energy Policy Act of 2005, the Owners are required to insure against public liability claims resulting from nuclear incidents to the full limit of public liability, which is currently $13.6 billion. This limit of liability consists of the maximum available commercial insurance of $0.4 billion and the remaining $13.2 billion is provided through an industry-wide retrospective assessment program mandated by law, known as the Secondary Financial Protection (SFP) program. Under the SFP program, the Owners can be assessed up to $127.3 million ($59.8 million, KCP&L's 47% share) per incident at any commercial reactor in the country, payable at no more than $19.0 million ($8.9 million, KCP&L's 47% share) per incident per year. This assessment is subject to an inflation adjustment based on the Consumer Price Index and applicable premium taxes. In addition, the U.S. Congress could impose additional revenue-raising measures to pay claims.
	Nuclear Property Insurance
	The Owners carry decontamination liability, premature decommissioning liability and property damage insurance from NEIL for Wolf Creek totaling approximately $2.8 billion ($1.3 billion, KCP&L's 47% share). In the event of an accident, insurance proceeds must first be used for reactor stabilization and site decontamination in accordance with a plan mandated by the NRC. KCP&L's share of any remaining proceeds can be used for further decontamination, property damage restoration and premature decommissioning costs. Premature decommissioning coverage applies only if an accident at Wolf Creek exceeds $500 million in property damage and decontamination expenses, and only after trust funds have been exhausted.
	Accidental Nuclear Outage Insurance
	The Owners also carry additional insurance from NEIL to cover costs of replacement power and other extra expenses incurred in the event of a prolonged outage resulting from accidental property damage at Wolf Creek.
	Under all NEIL policies, the Owners are subject to retrospective assessments if NEIL losses, for each policy year, exceed the accumulated funds available to the insurer under that policy. The estimated maximum amount of retrospective assessments under the current policies could total approximately $39.3 million ($18.5 million, KCP&L's 47% share) per policy year.

Regulatory_Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 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 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 Rate Case Proceedings
	In January 2015, KCP&L filed an application with the KCC to request an increase to its retail revenues of $67.3 million, with a return on equity of 10.3% and a rate-making equity ratio of 50.48%. The request includes costs to install environmental upgrades at the La Cygne Station, upgrades at Wolf Creek and other infrastructure and system improvements made to be able to provide reliable electric service. If approved, new rates are anticipated to be effective on or around October 1, 2015.
	In September 2014, KCC issued an order approving KCP&L to use budget amounts for its Kansas jurisdictional portion of costs to install environmental upgrades at the La Cygne Station in determining its request for new retail rates in this general rate case. KCP&L is also allowed 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 this Kansas general rate case. The La Cygne project is expected to be in-service by June 2015.
	KCP&L Missouri Rate Case Proceedings
	In October 2014, KCP&L filed an application with the MPSC to request an increase to its retail revenues of $120.9 million, with a return on equity of 10.3% and a rate-making equity ratio of 50.36%. The request includes recovery of increased transmission and property tax expenses, costs to install environmental upgrades at the La Cygne Station, upgrades at Wolf Creek and other infrastructure and system improvements made to be able to provide reliable electric service. KCP&L also requested authorization to implement a Fuel Adjustment Clause (FAC). If approved, new rates are anticipated to be effective on or around September 30, 2015.
	In January 2015, the MPSC issued an order approving KCP&L's continued use of construction accounting for its 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. The La Cygne project is expected to be in-service by June 2015.
	Regulatory Assets and Liabilities
	Great Plains Energy and KCP&L have recorded assets and liabilities on their consolidated balance sheets resulting from the effects of the ratemaking process, which would not otherwise be recorded if the Companies were not regulated. Regulatory assets represent incurred costs that are probable of recovery from future revenues. Regulatory liabilities represent future reductions in revenues or refunds to customers.
	Management regularly assesses whether regulatory assets and liabilities are probable of future recovery or refund by considering factors such as decisions by the MPSC, KCC or FERC in KCP&L's and GMO's rate case filings; decisions in other regulatory proceedings, including decisions related to other companies that establish precedent on matters applicable to the Companies; and changes in laws and regulations. If recovery or refund of regulatory assets or liabilities is not approved by regulators or is no longer deemed probable, these regulatory assets or liabilities are recognized in the current period results of operations. The Companies' continued ability to meet the criteria for recording regulatory assets and liabilities may be affected in the future by restructuring and deregulation in the electric industry or changes in accounting rules. In the event that the criteria no longer applied to any or all of the Companies' operations, the related regulatory assets and liabilities would be written off unless an appropriate regulatory recovery mechanism were provided. Additionally, these factors could result in an impairment on utility plant assets.
	Great Plains Energy's and KCP&L's regulatory assets and liabilities are detailed in the following table.
		December 31
		2014								2013
		KCP&L			GMO			Great Plains Energy		KCP&L		GMO		Great Plains Energy
	Regulatory Assets	(millions)
	Taxes recoverable through future rates	$	107.1		$	26.3		$	133.4	$	111	$	25.4	$	136.4
	Loss on reacquired debt	8.1		(a)	2.8		(a)	10.9		7.1		1.5		8.6
	Cost of removal	2.8			—			2.8		1		—		1
	Asset retirement obligations	38.1			17.2			55.3		34.8		16		50.8
	Pension and post-retirement costs	430.5		(b)	95.4		(b)	525.9		310		91.2		401.2
	Deferred customer programs	50.8		(c)	18.8		(d)	69.6		50.2		21.8		72
	Rate case expenses	1.4		(e)	0.1			1.5		3.6		0.6		4.2
	Fuel recovery mechanism	13		(e)	41		(e)	54		10.8		12.8		23.6
	Acquisition transition costs	7		(f)	6.6		(f)	13.6		12.9		11		23.9
	Derivative instruments	0.2		(g)	2.6		(g)	2.8		—		—		—
	Iatan No. 1 and common facilities depreciation and carrying costs	14.7		(h)	5.5		(h)	20.2		15.3		5.7		21
	Iatan No. 2 construction accounting costs	28.1		(i)	15.3		(i)	43.4		29.3		16		45.3
	Kansas property tax surcharge	6.1		(e)	—			6.1		4		—		4
	Solar rebates	29.1		(e)	56.9		(e)	86		13		32.3		45.3
	Voluntary separation program	2.5		(j)	—			2.5		3.4		—		3.4
	Other	6.2		(e)	0.4		(e)	6.6		7.7		1.3		9
	Total	$	745.7		$	288.9		$	1,034.60	$	614.1	$	235.6	$	849.7
	Regulatory Liabilities
	Emission allowances	$	70.1		$	—		$	70.1	$	74	$	—	$	74
	Asset retirement obligations	93.9			—			93.9		86.2		—		86.2
	Cost of removal	—			69.7		(k)	69.7		—		68.1		68.1
	Other	8			41			49		8.1		27.6		35.7
	Total	$	172		$	110.7		$	282.7	$	168.3	$	95.7	$	264
	(a) Amortized over the life of the related new debt issuances or the remaining lives of the old debt issuances if no new debt was issued.
	(b) Represents unrecognized gains and losses, prior service and transition costs that will be recognized in future net periodic pension and post-retirement costs, pension settlements amortized over various periods and financial and regulatory accounting method differences that will be eliminated over the life of the pension plans. Of these amounts, $408.1 million and $55.7 million for KCP&L and GMO, respectively, are not included in rate base and are amortized over various periods.
	(c) $22.0 million not included in rate base and amortized over various periods.
	(d) $2.2 million not included in rate base and amortized over various periods.
	(e) Not included in rate base and amortized over various periods.
	(f) Not included in rate base and amortized through 2016.
	(g) Represents fair value of derivative instruments for commodity contracts. Settlements of the contracts are recognized in the income
	statement and included in fuel recovery mechanisms.
	(h) Included in rate base and amortized through 2038.
	(i) Included in rate base and amortized through 2058.
	(j) Not included in rate base and amortized through 2017.
	(k) Estimated cumulative net provision for future removal costs.

Goodwill_and_Intangible_Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets [Text Block]	6. GOODWILL AND INTANGIBLE ASSETS
	Accounting rules require goodwill to be tested for impairment annually and when an event occurs indicating the possibility that an impairment exists. The annual impairment test for the $169.0 million of GMO acquisition goodwill was conducted on September 1, 2014. The goodwill impairment test is a two step process. The first step compares the fair value of a reporting unit to its carrying amount, including goodwill, to identify potential impairment. If the carrying amount exceeds the fair value of the reporting unit, the second step of the test is performed, consisting of assignment of the reporting unit's fair value to its assets and liabilities to determine an implied fair value of goodwill, which is compared to the carrying amount of goodwill to determine the impairment loss, if any, to be recognized in the financial statements. Great Plains Energy's regulated electric utility operations are considered one reporting unit for assessment of impairment, as they are included within the same operating segment and have similar economic characteristics. The determination of fair value of the reporting unit consisted of two valuation techniques: an income approach consisting of a discounted cash flow analysis and a market approach consisting of a determination of reporting unit invested capital using market multiples derived from the historical revenue, EBITDA, net utility asset values and market prices of stock of peer companies. The results of the two techniques were evaluated and weighted to determine a point within the range that management considered representative of fair value for the reporting unit. Fair value of the reporting unit substantially exceeded the carrying amount, including goodwill; therefore, there was no impairment of goodwill.
	Great Plains Energy's and KCP&L's intangible assets are included in electric utility plant on the consolidated balance sheets and are detailed in the following table.
			December 31, 2014									December 31, 2013
		Gross Carrying Amount					Accumulated Amortization				Gross Carrying Amount					Accumulated Amortization
	Great Plains Energy	(millions)
	Computer software		$	300.2				$	(190.9	)		$	255.4				$	(169.9	)
	Asset improvements		27.4					(5.5		)		26.5					(4.9		)
	KCP&L
	Computer software		$	277.9				$	(175.5	)		$	231.2				$	(156.5	)
	Asset improvements		12.2					(1.3		)		11.2					(1.1		)
	Great Plains Energy's and KCP&L's amortization expense related to intangible assets is detailed in the following table.
		2014			2013
		(millions)
	Great Plains Energy	$	21.6		$	17.6
	KCP&L	19.2			14.3
	The following table provides the estimated amortization expense related to Great Plains Energy's and KCP&L's intangible assets for 2015 through 2019 for the intangible assets included in the consolidated balance sheets at December 31, 2014.
		2015			2016				2017		2018			2019
		(millions)
	Great Plains Energy	$	24.2		$	19			$	15	$	12.1		$	9.2
	KCP&L	21.8			16.1				13.9		11.7			8.8

Asset_Retirement_Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations [Text Block]	7. ASSET RETIREMENT OBLIGATIONS
	Asset retirement obligations associated with tangible long-lived assets are those for which a legal obligation exists under enacted laws, statutes and written or oral contracts, including obligations arising under the doctrine of promissory estoppel. These liabilities are recognized at estimated fair value as incurred with a corresponding amount capitalized as part of the cost of the related long-lived assets and depreciated over their useful lives. Accretion of the liabilities due to the passage of time is recorded to a regulatory asset and/or liability. Changes in the estimated fair values of the liabilities are recognized when known.
	KCP&L has AROs related to decommissioning Wolf Creek, site remediation of its Spearville Wind Energy Facilities, asbestos abatement and removal of storage tanks, ash ponds and landfills. GMO has AROs related to asbestos abatement and removal of storage tanks, ash ponds and landfills.
	Additionally, certain wiring used in Great Plains Energy's and KCP&L's generating stations include asbestos insulation, which would require special handling if disturbed. Due to the inability to reasonably estimate the quantities or the amount of disturbance that will be necessary during dismantlement at the end of the life of a plant, the fair value of this ARO cannot be reasonably estimated at this time. Management will continue to monitor the obligation and will recognize a liability in the period in which sufficient information becomes available to reasonably estimate its fair value.
	The MPSC and KCC require KCP&L and the other owners of Wolf Creek to submit an updated decommissioning cost study every three years. The most recent study was submitted in August 2014. As a result of the new cost estimate, KCP&L increased its ARO to decommission Wolf Creek by $23.9 million.
	The following table summarizes the change in Great Plains Energy's and KCP&L's AROs.
		Great Plains Energy				KCP&L
		2014		2013		2014		2013
		(millions)
	Beginning balance	$	158.8	$	149.3	$	141.7	$	133.2
	Revision in timing and/or estimates - Wolf Creek	23.9		—		23.9		—
	Revision in timing and/or estimates - other	2.9		—		2.9		—
	Accretion	10.3		9.5		9.2		8.5
	Ending balance	$	195.9	$	158.8	$	177.7	$	141.7

Pension_Plans_and_Other_Employ

Pension Plans and Other Employee Benefits	12 Months Ended
	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Pension Plans and Other Employee Benefits	8. PENSION PLANS, OTHER EMPLOYEE BENEFITS AND VOLUNTARY SEPARATION PROGRAM
	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 in 2014, the 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.
	In 2014, 2013 and 2012, Great Plains Energy incurred pension settlement charges of $8.5 million, $4.9 million and $0.8 million, respectively, as a result of accelerated pension distributions.
	The following pension benefits tables provide information relating to the funded status of all defined benefit pension plans on an aggregate basis as well as the components of net periodic benefit costs. For financial reporting purposes, the market value of plan assets is the fair value. For regulatory reporting purposes, a five-year smoothing of assets is used to determine fair value. Net periodic benefit costs reflect total plan benefit costs prior to the effects of capitalization and sharing with joint owners of power plants.
			Pension Benefits								Other Benefits
			2014				2013				2014				2013
	Change in projected benefit obligation (PBO)		(millions)
	PBO at January 1		$	1,007.40			$	1,130.50			$	160.5			$	186.5
	Service cost		36.7				41.2				3.7				4.4
	Interest cost		50.1				47.2				7.9				7.7
	Contribution by participants		—				—				6.8				6.2
	Amendments		—				0.3				—				(6.0		)
	Actuarial (gain) loss		181.1				(118.4		)		(0.3		)		(26.1		)
	Benefits paid		(49.0		)		(52.9		)		(13.4		)		(12.2		)
	Settlements		(39.5		)		(40.5		)		—				—
	PBO at December 31		$	1,186.80			$	1,007.40			$	165.2			$	160.5
	Change in plan assets
	Fair value of plan assets at January 1		$	703			$	666.4			$	101.2			$	90.3
	Actual return on plan assets		47.2				70.9				4.1				(2.0		)
	Contributions by employer and participants		66.2				57.4				18.6				25
	Benefits paid		(46.9		)		(51.2		)		(13.3		)		(12.1		)
	Settlements		(39.5		)		(40.5		)		—				—
	Fair value of plan assets at December 31		$	730			$	703			$	110.6			$	101.2
	Funded status at December 31		$	(456.8	)		$	(304.4	)		$	(54.6	)		$	(59.3	)
	Amounts recognized in the consolidated balance sheets
	Current pension and other post-retirement liability		$	(1.9	)		$	(2.3	)		$	(0.9	)		$	(0.9	)
	Noncurrent pension liability and other post-retirement liability		(454.9		)		(302.1		)		(53.7		)		(58.4		)
	Net amount recognized before regulatory treatment		(456.8		)		(304.4		)		(54.6		)		(59.3		)
	Accumulated OCI or regulatory asset/liability		500.5				368.3				26.1				35.3
	Net amount recognized at December 31		$	43.7			$	63.9			$	(28.5	)		$	(24.0	)
	Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
	Actuarial loss		$	273.5			$	147.7			$	17.5			$	19.2
	Prior service cost		4.7				5.6				13.5				16.6
	Transition obligation		—				—				0.2				0.4
	Other		222.3				215				(5.1		)		(0.9		)
	Net amount recognized at December 31		$	500.5			$	368.3			$	26.1			$	35.3
			Pension Benefits												Other Benefits
			2014				2013				2012				2014				2013			2012
	Components of net periodic benefit costs		(millions)
	Service cost		$	36.7			$	41.2			$	35.4			$	3.7			$	4.4		$	3.3
	Interest cost		50.1				47.2				48.9				7.9				7.7			7.8
	Expected return on plan assets		(50.2		)		(47.1		)		(42.9		)		(2.6		)		(2.0		)	(1.8		)
	Prior service cost		0.9				2				4.5				3.1				7.2			7.1
	Recognized net actuarial (gain) loss		50				54.3				44.5				(0.1		)		1.7			(0.2		)
	Transition obligation		—				—				—				0.2				0.2			1.1
	Settlement charges		8.5				4.9				0.8				—				—			—
	Net periodic benefit costs before regulatory adjustment		96				102.5				91.2				12.2				19.2			17.3
	Regulatory adjustment		(11.3		)		(16.8		)		(15.5		)		4.3				(2.4		)	1.5
	Net periodic benefit costs		84.7				85.7				75.7				16.5				16.8			18.8
	Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
	Current year net (gain) loss		175.8				(147.0		)		97.9				(1.8		)		(22.1		)	27.1
	Amortization of gain (loss)		(50.0		)		(54.3		)		(44.5		)		0.1				(1.7		)	0.2
	Prior service cost		—				0.3				1.1				—				(6.0		)	—
	Amortization of prior service cost		(0.9		)		(2.0		)		(4.5		)		(3.1		)		(7.2		)	(7.1		)
	Amortization of transition obligation		—				—				—				(0.2		)		(0.2		)	(1.1		)
	Other regulatory activity		7.3				11.8				17.7				(4.2		)		2.1			(1.2		)
	Total recognized in OCI or regulatory asset/liability		132.2				(191.2		)		67.7				(9.2		)		(35.1		)	17.9
	Total recognized in net periodic benefit costs and OCI or regulatory asset/liability		$	216.9			$	(105.5	)		$	143.4			$	7.3			$	(18.3	)	$	36.7
	For financial reporting purposes, the estimated prior service cost and net loss for the defined benefit plans that will be amortized from accumulated OCI or a regulatory asset into net periodic benefit cost in 2015 are $0.8 million and $51.4 million, respectively. For financial reporting purposes, net actuarial gains and losses are recognized on a rolling five-year average basis. For regulatory reporting purposes, net actuarial gains and losses are amortized over ten years. The estimated prior service cost, net loss and transition costs for the other post-retirement benefit plans that will be amortized from accumulated OCI or a regulatory asset into net periodic benefit cost in 2015 are $3.1 million, $0.2 million and $0.2 million, respectively.
	The accumulated benefit obligation (ABO) for all defined benefit pension plans was $1,036.8 million and $889.2 million at December 31, 2014 and 2013, respectively. Pension and other post-retirement benefit plans with the PBO, ABO or accumulated other post-retirement benefit obligation (APBO) in excess of the fair value of plan assets at year-end are detailed in the following table.
			2014				2013
	Pension plans with the PBO in excess of plan assets		(millions)
	Projected benefit obligation		$	1,186.80			$	1,007.40
Fair value of plan assets		730				703
Pension plans with the ABO in excess of plan assets
Accumulated benefit obligation		$	1,036.80			$	889.2
Fair value of plan assets		730				703
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated other post-retirement benefit obligation		$	165.2			$	160.5
Fair value of plan assets		110.6				101.2
The GMO Supplemental Executive Retirement Plan (SERP) is reflected as an unfunded ABO of $24.2 million. Great Plains Energy has approximately $17.5 million of assets in a non-qualified trust for this plan as of December 31, 2014, and expects to fund future benefit payments from these assets.
The expected long-term rate of return on plan assets represents Great Plains Energy's estimate of the long-term return on plan assets and is based on historical and projected rates of return for current and planned asset classes in the plans' investment portfolios. Assumed projected rates of return for each asset class were selected after analyzing historical experience and future expectations of the returns of various asset classes. Based on the target asset allocation for each asset class, the overall expected rate of return for the portfolios was developed and adjusted for the effect of projected benefits paid from plan assets and future plan contributions. The following tables provide the weighted-average assumptions used to determine benefit obligations and net costs.
Weighted-average assumptions used to determine the benefit obligation at December 31		Pension Benefits										Other Benefits
		2014					2013					2014					2013
Discount rate		4.22	%				5.03	%				4.14	%				4.92	%
Rate of compensation increase		3.62	%				3.69	%				3.5	%				3.5	%
Weighted-average assumptions used to determine net costs for years ended December 31		Pension Benefits										Other Benefits
		2014					2013					2014					2013
Discount rate		5.03	%				4.17	%				4.92	%				4.13	%
Expected long-term return on plan assets		7.24	%				7.24	%				2.7	%	*			2.62	%	*
Rate of compensation increase		3.69	%				3.69	%				3.5	%				3.5	%
*after tax
As of December 31, 2014, Great Plains Energy adopted a new mortality table published by the Society of Actuaries in October 2014 which reflected longer expected lives for plan participants. This longer mortality assumption, in addition to the decrease in discount rate assumptions from 2013 to 2014, were the primary causes of the $181.1 million actuarial loss increase in the projected benefit obligation for pension benefits in 2014.
Great Plains Energy expects to contribute $78.9 million to the pension plans in 2015 to meet Employee Retirement Income Security Act of 1974, as amended (ERISA) funding requirements and regulatory orders, the majority of which is expected to be paid by KCP&L. Great Plains Energy's funding policy is to contribute amounts sufficient to meet the ERISA funding requirements and MPSC and KCC rate orders plus additional amounts as considered appropriate; therefore, actual contributions may differ from expected contributions. Great Plains Energy also expects to contribute $10.2 million to other post-retirement benefit plans in 2015, the majority of which is expected to be paid by KCP&L.
The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid through 2024.
		Pension Benefits				Other Benefits
		(millions)
2015		$	76.5			$	7.5
2016		74.9				8.1
2017		76.7				8.6
2018		78.2				9
2019		80.2				9.4
2020-2024		420.6				49.7
Pension plan assets are managed in accordance with prudent investor guidelines contained in the ERISA requirements. The investment strategy supports the objective of the fund, which is to earn the highest possible return on plan assets within a reasonable and prudent level of risk. The portfolios are invested, and periodically rebalanced, to achieve targeted allocations of approximately 33% U.S. large cap and small cap equity securities, 20% international equity securities, 35% fixed income securities, 7% real estate, 1% commodities and 4% hedge funds. Fixed income securities include domestic and foreign corporate bonds, collateralized mortgage obligations and asset-backed securities, U.S. government agency, state and local obligations, U.S. Treasury notes and money market funds.
The fair values of Great Plains Energy's pension plan assets at December 31, 2014 and 2013, by asset category are in the following tables.
						Fair Value Measurements Using
	December 31					Quoted Prices in Active Markets for Identical Assets						Significant Other Observable Inputs						Significant Unobservable Inputs
	2014					(Level 1)						(Level 2)						(Level 3)
Description
		(millions)
Pension Plans
Equity securities
U.S. (a)		$	235.2				$	203.6					$	31.6					$	—
International (b)		147.3					108.4						38.9						—
Real estate (c)		38.9					7.7						6.3						24.9
Commodities (d)		5.9					—						5.9						—
Fixed income securities
Fixed income funds (e)		66.1					22.3						43.8						—
U.S. Treasury		44.2					44.2						—						—
U.S. Agency, state and local obligations		21					—						21						—
U.S. corporate bonds (f)		109					—						109						—
Foreign corporate bonds		13.6					—						13.6						—
Hedge funds (g)		24.1					—						—						24.1
Cash equivalents		16.7					16.7						—						—
Other		8					—						8						—
Total		$	730				$	402.9					$	278.1					$	49
						Fair Value Measurements Using
	December 31					Quoted Prices in Active Markets for Identical Assets						Significant Other Observable Inputs						Significant Unobservable Inputs
	2013					(Level 1)						(Level 2)						(Level 3)
Description
		(millions)
Pension Plans
Equity securities
U.S. (a)		$	193.7				$	80.5					$	113.2					$	—
International (b)		167.1					39.9						127.2						—
Real estate (c)		49.1					—						5.4						43.7
Commodities (d)		34.8					—						34.8						—
Fixed income securities
Fixed income funds (e)		181.3					27.1						154.2						—
U.S. Treasury		2.6					2.6						—						—
U.S. Agency, state and local obligations		17.1					—						17.1						—
U.S. corporate bonds (f)		25.6					—						25.6						—
Foreign corporate bonds		2.3					—						2.3						—
Hedge funds (g)		23.1					—						—						23.1
Cash equivalents		3					3						—						—
Other		3.3					—						3.3						—
Total		$	703				$	153.1					$	483.1					$	66.8
(a) At December 31, 2014 and 2013, this category is comprised of $78.1 million and $80.5 million, respectively, of traded mutual funds valued at daily listed prices and $31.6 million and $113.2 million, respectively, of institutional common/collective trust funds valued at Net Asset Value (NAV) per share. At December 31, 2014, this category also included $125.5 million of traded common stocks and exchange traded funds.
(b) At December 31, 2014 and 2013, this category is comprised of $38.6 million and $39.9 million, respectively, of traded mutual funds valued at daily listed prices and $38.6 million and $127.2 million, respectively, of institutional common/collective trust funds valued at daily NAV per share. At December 31, 2014, this category also included $70.1 million of traded American depository receipts, global depository receipts and ordinary shares.
(c) At December 31, 2014 and 2013, this category is comprised of $7.7 million and none, respectively, of traded real estate investment trusts, $12.7 million and $32.6 million, respectively, of institutional common/collective trust funds and $18.5 million and $16.5 million, respectively, of a limited partnership valued at NAV on a quarterly basis.
(d) This category is comprised of institutional common/collective trust funds valued at daily NAV per share.
(e) At December 31, 2014 and 2013, this category is comprised of $22.3 million and $27.1 million, respectively, of traded mutual funds valued at daily listed prices and $43.8 million and $154.2 million, respectively, of institutional common/collective trust funds valued at daily NAV per share.
(f) At December 31, 2014 and 2013, this category is comprised of $100.3 million and $20.1 million, respectively, of corporate bonds, $4.0 million and $3.6 million, respectively, of collateralized mortgage obligations and $4.7 million and $1.9 million, respectively, of other asset-backed securities.
(g) This category is comprised of closely-held limited partnerships valued at NAV on a quarterly basis.
The following tables reconcile the beginning and ending balances for all level 3 pension plan assets measured at fair value on a recurring basis for 2014 and 2013.
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Description		Real Estate						Hedge Funds					Total
		(millions)
Balance January 1, 2014			$	43.7					$	23.1					$	66.8
Actual return on plan assets
Relating to assets still held			3.1						1						4.1
Relating to assets sold			1.2						—						1.2
Purchase, sales and settlements, net			(23.1		)				—						(23.1		)
Balance December 31, 2014			$	24.9					$	24.1					$	49
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Description		Real Estate						Hedge Funds						Total
		(millions)
Balance January 1, 2013			$	38.4					$	21.6					$	60
Actual return on plan assets
Relating to assets still held			4.6						1.5						6.1
Purchase, sales and settlements, net			0.7						—						0.7
Balance December 31, 2013			$	43.7					$	23.1					$	66.8
Other post-retirement plan assets are also managed in accordance with prudent investor guidelines contained in the ERISA requirements. The investment strategy supports the objective of the funds, which is to preserve capital, maintain sufficient liquidity and earn a consistent rate of return. Other post-retirement plan assets are invested primarily in fixed income securities, which may include domestic and foreign corporate bonds, collateralized mortgage obligations and asset-backed securities, U.S. government agency, state and local obligations, U.S. Treasury notes and money market funds, as well as domestic and international equity funds.
The fair values of Great Plains Energy's other post-retirement plan assets at December 31, 2014 and 2013, by asset category are in the following tables.
						Fair Value Measurements Using
	December 31					Quoted Prices in Active Markets for Identical Assets						Significant Other Observable Inputs						Significant Unobservable Inputs
	2014					(Level 1)						(Level 2)						(Level 3)
Description
		(millions)
Other Post-Retirement Benefit Plans
Equity securities		$	3.2				$	3.2					$	—					$	—
Fixed income securities
Fixed income fund (a)		73					0.2						72.8						—
U.S. Treasury		2.7					2.7						—						—
U.S. Agency, state and local obligations		4.9					—						4.9						—
U.S. corporate bonds (b)		13					—						13						—
Foreign corporate bonds		1.5					—						1.5						—
Cash equivalents		10.4					10.4						—						—
Other		1.9					—						1.9						—
Total		$	110.6				$	16.5					$	94.1					$	—
						Fair Value Measurements Using
	December 31					Quoted Prices in Active Markets for Identical Assets						Significant Other Observable Inputs						Significant Unobservable Inputs
	2013					(Level 1)						(Level 2)						(Level 3)
Description
		(millions)
Other Post-Retirement Benefit Plans
Equity securities		$	2.2				$	2.2					$	—					$	—
Fixed income securities
Fixed income fund (a)		74.6					0.2						74.4						—
U.S. Treasury		1.5					1.5						—						—
U.S. Agency, state and local obligations		4.4					—						4.4						—
U.S. corporate bonds (b)		8.6					—						8.6						—
Foreign corporate bonds		1					—						1						—
Cash equivalents		8.6					8.6						—						—
Other		0.3					—						0.3						—
Total		$	101.2				$	12.5					$	88.7					$	—
(a) At December 31, 2014 and 2013, this category is comprised of $72.8 million and $74.4 million, respectively, of an institutional common/collective trust fund valued at daily NAV per share and $0.2 million of traded mutual funds valued at daily listed prices.
(b) At December 31, 2014 and 2013, this category is comprised of $10.3 million and $7.1 million, respectively, of corporate bonds, $0.8 million and $0.3 million, respectively, of collateralized mortgage obligations and $1.9 million and $1.2 million, respectively, of other asset-backed securities.
Assumed health care cost trend rates have a significant effect on the amounts reported for the health care plans. The cost trend assumed for both 2014 and 2015 was 7.0%, with the rate declining through 2025 to the ultimate cost trend rate of 4.5%. The health care plan requires retirees to make monthly contributions on behalf of themselves and their dependents in an amount determined by Great Plains Energy.
The effects of a one-percentage point change in the assumed health care cost trend rates, holding all other assumptions constant, at December 31, 2014, are detailed in the following table.
		Increase				Decrease
		(millions)
Effect on total service and interest component		$	0.9			$	(1.1	)
Effect on post-retirement benefit obligation		7.4				(6.1		)
Employee Savings Plans
Great Plains Energy has defined contribution savings plans (401(k)) that cover substantially all employees. Great Plains Energy matches employee contributions, subject to limits. The annual cost of the plans was approximately $9.7 million in 2014, $9.6 million in 2013, and $9.2 million in 2012. KCP&L's annual cost of the plans was approximately $7.1 million in 2014, $7.0 million in 2013, and $6.7 million in 2012.
Voluntary Separation Program
In 2011, Great Plains Energy executed an organizational realignment and voluntary separation program to assist in the management of overall costs within the level reflected in the Company's retail electric rates and to enhance organizational efficiency.  In 2012, KCP&L deferred $4.3 million of expense related to the voluntary separation program to a regulatory asset for recovery in rates beginning January 1, 2013, pursuant to KCP&L's December 2012 KCC rate order.

Equity_Compensation

Equity Compensation	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity Compensation	9. 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. The maximum number of shares of Great Plains Energy common stock that can be issued under the plan is 8.0 million. Common stock shares delivered by Great Plains Energy under the Long-Term Incentive Plan may be authorized but unissued, held in the treasury or purchased on the open market (including private purchases) in accordance with applicable securities laws. Great Plains Energy has a policy of delivering newly issued shares, or shares surrendered by Long-Term Incentive Plan participants for the withholding of taxes and held in treasury, or both, and does not expect to repurchase common shares during 2015 to satisfy performance share payments and director deferred share unit conversion. 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.
			2014		2013				2012
	Great Plains Energy		(millions)
	Equity compensation expense		$	9.9	$	5.6			$	3.3
	Income tax benefit		3.6		1.9				1.4
	KCP&L
	Equity compensation expense		$	6.9	$	4			$	2.3
	Income tax benefit		2.4		1.3				1
	Performance Shares
	The payment of performance shares is contingent upon achievement of specific performance goals over a stated period of time as approved by the Compensation and Development Committee of the Board. The number of performance shares ultimately paid can vary from the number of shares initially granted depending on Great Plains Energy's performance over stated performance periods. Compensation expense for performance shares is calculated by taking the change in fair value between reporting periods for the portion for which the requisite service has been rendered. Dividends are accrued over the vesting period and paid in cash based on the number of performance shares ultimately paid.
	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.
	Performance share activity is summarized in the following table. Performance adjustment represents the number of shares of common stock related to performance shares ultimately issued that can vary from the number of performance shares initially granted depending on Great Plains Energy's performance over a stated period of time.
		Performance			Grant Date
		Shares			Fair Value*
	Beginning balance January 1, 2014		430,009			$	23.52
	Granted		214,946			28.78
	Earned		(107,741	)		26.14
	Forfeited		(2,927	)		25.73
	Performance adjustment		(271	)
	Ending balance December 31, 2014		534,016			25.11
	* weighted-average
	At December 31, 2014, the remaining weighted-average contractual term was 1.2 years.  The weighted-average grant-date fair value of shares granted was $28.78, $24.17 and $19.37 in 2014, 2013 and 2012, respectively. At December 31, 2014, there was $8.8 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 in 2014 and $2.4 million in 2013. There were no performance shares earned and paid in 2012.
	Restricted Stock
	Restricted stock cannot be sold or otherwise transferred by the recipient prior to vesting and has a value equal to the fair market value of the shares on the issue date. Restricted stock shares vest over a stated period of time with accruing reinvested dividends subject to the same restrictions. Compensation expense, calculated by multiplying shares by the grant-date fair value related to restricted stock, is recognized over the stated vesting period. Restricted stock activity 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		81,290			25.7
	Vested		(101,174	)		18.96
	Forfeited		(1,263	)		24.16
	Ending balance December 31, 2014		267,390			22.31
	* weighted-average
	At December 31, 2014, the remaining weighted-average contractual term was 1.1 years.  The weighted-average grant-date fair value of shares granted was $25.70, $22.47 and $19.75 in 2014, 2013 and 2012, respectively.  At December 31, 2014, there was $2.3 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 $1.9 million, $1.2 million and $3.3 million in 2014, 2013 and 2012, respectively.
	Director Deferred Share Units
	Non-employee directors receive shares of Great Plains Energy's common stock as part of their annual retainer. Each director may elect to defer receipt of their shares until the end of January in the year after they leave the Board or such other time as elected by each director. Director Deferred Share Units have a value equal to the market value of Great Plains Energy's common stock on the grant date with accruing dividends. Compensation expense, calculated by multiplying the director deferred share units by the related grant-date fair value, is recognized at the grant date. The total fair value of shares of Director Deferred Share Units issued was insignificant for 2014 and 2013. Director Deferred Share Units activity is summarized in the following table.
			Share Units			Grant Date Fair Value*
	Beginning balance January 1, 2014			90,120			$	20.94
	Issued			20,621			26.53
	Ending balance December 31, 2014			110,741			21.98
	* weighted-average

Shortterm_Borrowings_and_Short

Short-term Borrowings and Short-term Bank Lines of Credit	12 Months Ended
	Dec. 31, 2014
Short-term Borrowings and Short-term Bank Lines of Credit [Abstract]
Short-term Borrowings and Short-term Bank Lines of Credit [Text Block]	10. SHORT-TERM BORROWINGS AND SHORT-TERM BANK LINES OF CREDIT
	Great Plains Energy's $200 Million Revolving Credit Facility
	In December 2014, Great Plains Energy entered into an amendment to its $200 million revolving credit facility with a group of banks to extend the term to October 2019 from 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 December 31, 2014, Great Plains Energy was in compliance with this covenant.  At December 31, 2014, Great Plains Energy had $4.0 million of outstanding cash borrowings at a weighted-average interest rate of 1.69% and had 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
	In December 2014, KCP&L entered into an amendment to its $600 million revolving credit facility with a group of banks that provides support for its issuance of commercial paper and other general corporate purposes to extend the term to October 2019 from 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 December 31, 2014, KCP&L was in compliance with this covenant.  At December 31, 2014, KCP&L had $358.3 million of commercial paper outstanding at a weighted-average interest rate of 0.48%, 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
	In December 2014, GMO entered into an amendment to its $450 million revolving credit facility with a group of banks that provides support for its issuance of commercial paper and other general corporate purposes to extend the term to October 2019 from 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 December 31, 2014, GMO was in compliance with this covenant.  At December 31, 2014, GMO had no commercial paper outstanding, had issued letters of credit totaling $3.2 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	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Long-Term Debt	11. LONG-TERM DEBT
	Great Plains Energy's and KCP&L's long-term debt is detailed in the following table.
				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
	0.05% 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				(3.8		)			(4.1		)
	Total KCP&L excluding current maturities				2,298.50					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				4.3					4.9
	Total Great Plains Energy excluding current maturities				$	3,488.00				$	3,515.70
	(a)	Weighted-average interest rates at December 31, 2014
	(b)	Rate after amortizing gains/losses recognized in OCI on settlements of interest rate hedging instruments
	(c)	Variable rate
	Amortization of Debt Expense
	Great Plains Energy's and KCP&L's amortization of debt expense is detailed in the following table.
			2014				2013			2012
			(millions)
	KCP&L		$	3			$	3.2		$	2.9
	Other Great Plains Energy		1.8				2.5			2.6
	Total Great Plains Energy		$	4.8			$	5.7		$	5.5
	KCP&L General Mortgage Bonds
	KCP&L has issued mortgage bonds under the General Mortgage Indenture and Deed of Trust dated December 1, 1986, as supplemented (Indenture). The Indenture creates a mortgage lien on substantially all of KCP&L's utility plant. Mortgage bonds totaling $596.4 million were outstanding at December 31, 2014 and 2013.
	KCP&L Municipal Bond Insurance Policies
	KCP&L's secured and unsecured Series 2005 Environmental Improvement Revenue Refunding (EIRR) bonds totaling $35.9 million and $50.0 million, respectively, are covered by a municipal bond insurance policy between KCP&L and Syncora Guarantee, Inc. (Syncora). The insurance agreements between KCP&L and Syncora provide for reimbursement by KCP&L for any amounts that Syncora pays under the municipal bond insurance policies. The insurance agreements contain a covenant that the indebtedness to total capitalization ratio of KCP&L and its consolidated subsidiaries will not be greater than 0.68 to 1.00. At December 31, 2014, KCP&L was in compliance with this covenant. KCP&L is also restricted from issuing additional bonds under its General Mortgage Indenture if, after giving effect to such additional bonds, the proportion of secured debt to total indebtedness would be more than 75%, or more than 50% if the long term rating for such bonds by Standard & Poor's or Moody's Investors Service would be at or below A- or A3, respectively. The insurance agreement covering the unsecured Series 2005 EIRR bonds also required KCP&L to provide collateral to Syncora in the form of $50.0 million of Mortgage Bonds Series 2005 EIRR Insurer due 2035 for KCP&L's obligations under the insurance agreement as a result of KCP&L issuing general mortgage bonds in 2009 (other than refunding of outstanding general mortgage bonds) that resulted in the aggregate amount of outstanding general mortgage bonds exceeding 10% of total capitalization. The bonds are not incremental debt for KCP&L but collateralize Syncora's claim on KCP&L if Syncora was required to meet its obligation under the insurance agreement. In the event of a default under the insurance agreements, Syncora may take any available legal or equitable action against KCP&L, including seeking specific performance of the covenants.
	GMO First Mortgage Bonds
	GMO has issued mortgage bonds under the General Mortgage Indenture and Deed of Trust dated April 1, 1946, as supplemented. The Indenture creates a mortgage lien on substantially all of GMO's St. Joseph Light & Power division utility plant. Mortgage bonds totaling $7.9 million and $9.0 million, respectively, were outstanding at December 31, 2014 and 2013.
	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.
	GMO Senior Notes
	Under the terms of the note purchase agreement for GMO's Series A, B and C senior notes, GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the agreement, not greater than 0.65 to 1.00 at all times. In addition, GMO's priority debt, as defined in the agreement, cannot exceed 15% of consolidated tangible net worth, as defined in the agreement. At December 31, 2014, GMO was in compliance with these covenants.
	Scheduled Maturities
	Great Plains Energy's and KCP&L's long-term debt maturities for the next five years are detailed in the following table.
			2015				2016			2017			2018		2019
		(millions)
Great Plains Energy		$	15.1			$	1.1		$	382.1		$	351.1	$	401.1
KCP&L		14				—			281			350		400

Assets_Held_for_Sale_Assets_He

Assets Held for Sale Assets Held for Sale	12 Months Ended
	Dec. 31, 2014
Assets Held for Sale [Abstract]
Assets Held For Sale [Text Block]	12. 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, 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.

Common_Shareholders_Equity

Common Shareholders' Equity	12 Months Ended
	Dec. 31, 2014
Stockholders' Equity Note [Abstract]
Common Shareholders' Equity	13. COMMON SHAREHOLDERS' EQUITY
	Great Plains Energy has an effective shelf registration statement for the sale of unspecified amounts of securities with the Securities and Exchange Commission (SEC) that became effective in March 2012. A new shelf registration statement is expected to be filed in the first quarter of 2015.
	Great Plains Energy has 6.0 million shares of common stock registered with the SEC for its Dividend Reinvestment and Direct Stock Purchase Plan. The plan allows for the purchase of common shares by reinvesting dividends or making optional cash payments. Great Plains Energy can issue new shares or purchase shares on the open market for the plan. At December 31, 2014, 1.2 million shares remained available for future issuances.
	Great Plains Energy has 14.3 million shares of common stock registered with the SEC for a defined contribution savings plan. Shares issued under the plan may be either newly issued shares or shares purchased in the open market. At December 31, 2014, 1.3 million shares remained available for future issuances.
	Treasury shares are held for future distribution upon issuance of shares in conjunction with the Company's Long-Term Incentive Plan.
	Great Plains Energy's articles of incorporation restrict the payment of common stock dividends in the event common equity is 25% or less of total capitalization. In addition, if preferred stock dividends are not declared and paid when scheduled, Great Plains Energy could not declare or pay common stock dividends or purchase any common shares. If the unpaid preferred stock dividends equal four or more full quarterly dividends, the preferred shareholders, voting as a single class, could elect the smallest number of directors necessary to constitute a majority of the full Board. Certain conditions in the MPSC and KCC orders authorizing the holding company structure require Great Plains Energy and KCP&L to maintain consolidated common equity of at least 30% and 35%, respectively, of total capitalization (including only the amount of short-term debt in excess of the amount of construction work in progress). Under the Federal Power Act, KCP&L and GMO generally can pay dividends only out of retained earnings. The revolving credit agreements of Great Plains Energy, KCP&L and GMO and the note purchase agreement for GMO's Series A, B and C Senior Notes contain a covenant requiring the respective company to maintain a consolidated indebtedness to consolidated total capitalization ratio of not more than 0.65 to 1.00.
	As of December 31, 2014, all of Great Plains Energy's and KCP&L's retained earnings and net income were free of restrictions. As a result of the above restrictions, Great Plains Energy's subsidiaries had restricted net assets of approximately $2.8 billion as of December 31, 2014. The restrictions are not expected to affect the Companies' ability to pay dividends at the current level in the foreseeable future.

Preferred_Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2014
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock [Text Block]	14. PREFERRED STOCK
	At December 31, 2014, 1.6 million shares of Cumulative No Par Preferred Stock, 390,000 shares of Cumulative Preferred Stock, $100 par value and 11.0 million shares of no par Preference Stock were authorized under Great Plains Energy's articles of incorporation. All of the 390,000 authorized shares of Cumulative Preferred Stock are issued and outstanding. Great Plains Energy has the option to redeem the $39.0 million of issued Cumulative Preferred Stock at prices ranging from 101% to 103.7% of par value. If Great Plains Energy voluntarily files for dissolution or liquidation, the Cumulative Preferred Stock holders are entitled to receive the redemption prices. If a proceeding for dissolution or liquidation is filed against Great Plains Energy, the Cumulative Preferred Stock holders are entitled to receive the $100 par value per share plus accrued and unpaid dividends.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	15. 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 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 December 31, 2014, had incurred approximately $500 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 required reductions in SO2 and NOx emissions at Great Plains Energy's and KCP&L's fossil fuel-fired plants located in Missouri. The CAIR has been replaced with the CSAPR.
	The CSAPR requires states within its scope to reduce power plant SO2 and NOx emissions that contribute to ozone and fine particle nonattainment in other states. KCP&L and GMO are complying with the currently effective 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.  The La Cygne project is expected to be in-service by June 2015.
	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 became effective in April 2012 and 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 became effective in January 2013 and 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 subsequently installed a selective catalytic reduction (SCR) system at one of the three Jeffrey Energy Center units at a cost of approximately $225 million. Westar also installed less expensive NOx reduction equipment at the other two units. 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. 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.
	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, regulations or treaties 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 22 million tons and 17 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 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, which is anticipated to be finalized in the summer of 2015, 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 is 2012 CO2 emissions adjusted by the 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. The Clean Power plan is anticipated to be finalized in the summer of 2015.
	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.
	Kansas law currently requires certain utilities, including KCP&L, to have renewable energy generation capacity equal to at least 10% of their three-year average Kansas peak retail demand, increasing to 15% by 2016 and 20% by 2020.  Missouri law currently requires at least 5% of the electricity provided by certain utilities, including KCP&L and GMO, to come from renewable resources, including wind, solar, biomass and hydropower, increasing to 10% by 2018, and 15% by 2021, with a small portion (estimated to be about 2 MW for each of KCP&L and GMO) required to come from solar resources. Management believes that national renewable energy standards are also possible.  The timing, provisions and impact of such possible future requirements, including the cost to obtain and install new equipment to achieve compliance, cannot be reasonably estimated at this time.
	KCP&L and GMO project that they will be compliant with the Missouri renewable requirements, exclusive of the solar requirement, through 2035 and 2038.  KCP&L and GMO project that the acquisition of solar renewable energy credits will be sufficient for compliance with the Missouri solar requirements for the foreseeable future.  KCP&L also projects that it will be compliant with the Kansas renewable requirements through 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 such 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 the KDHE and the MDNR, 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 would set 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 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 December 2014, the EPA finalized regulations to regulate coal combustion residuals (CCRs) under the Resource Conservation and Recovery Act (RCRA) subtitle D to address the risks from the disposal of CCRs generated from the combustion of coal at electric generating facilities.  The Companies use coal in generating electricity and dispose of the CCRs in both on-site facilities and facilities owned by third parties.  The rule requires periodic assessments; groundwater monitoring; location restrictions; design and operating requirements; recordkeeping and notifications; and closure, among other requirements, for CCR units. The cost of complying with the CCR rule is currently being evaluated and has the potential of having a significant financial and operational impact on Great Plains Energy and KCP&L.  The rule is effective six months after promulgating in the Federal Register with various obligations effective at specified times within the rule.
	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 December 31, 2014 and 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 December 31, 2014 and 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 $1.4 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.
	Contractual Commitments
	Great Plains Energy's and KCP&L's expenses related to lease commitments are detailed in the following table.
		2014		2013			2012
		(millions)
	Great Plains Energy	$	16	$	18.5		$	21.8
	KCP&L	14		16			17.7
	Great Plains Energy's and KCP&L's contractual commitments at December 31, 2014, excluding pensions and long-term debt, are detailed in the following tables.
	Great Plains Energy
		2015			2016				2017		2018		2019		After 2019			Total
	Lease commitments	(millions)
	Operating lease	$	14.2		$	10			$	9.7	$	9.7	$	9		$	129.5		$	182.1
	Capital lease	0.4			0.4				0.4		0.4		0.4			4			6
	Purchase commitments
	Fuel	374.6			184.9				163		112.2		138.2			70.9			1,043.80
	Power	47.3			47.3				47.3		47.3		47.3			556.8			793.3
Capacity	3			1.2				—		—		—			—			4.2
La Cygne environmental project	16.6			—				—		—		—			—			16.6
Non-regulated natural gas transportation	3.5			3.5				1		—		—			—			8
Other	44.8			31.1				10		12.8		12			44.2			154.9
Total contractual commitments	$	504.4		$	278.4			$	231.4	$	182.4	$	206.9		$	805.4		$	2,208.90
KCP&L
	2015			2016				2017		2018		2019		After 2019			Total
Lease commitments	(millions)
Operating lease	$	12.8		$	9.9			$	9.7	$	9.7	$	9		$	129.5		$	180.6
Capital lease	0.2			0.2				0.2		0.2		0.2			2			3
Purchase commitments
Fuel	318.8			138.2				130.8		81.5		114.4			70.9			854.6
Power	34.8			34.8				34.8		34.8		34.8			394.6			568.6
Capacity	3			1.2				—		—		—			—			4.2
La Cygne environmental project	16.6			—				—		—		—			—			16.6
Other	41.1			29.7				8.6		11.4		10.6			36.2			137.6
Total contractual commitments	$	427.3		$	214			$	184.1	$	137.6	$	169		$	633.2		$	1,765.20
Great Plains Energy's and KCP&L's lease commitments end in 2048. Operating lease commitments include rail cars to serve jointly-owned generating units where KCP&L is the managing partner. Of the amounts included in the table above, KCP&L will be reimbursed by the other owners for approximately $1.9 million in 2015 and approximately $0.4 million per year from 2016 to 2025, for a total of $6.1 million.
Fuel commitments consist of commitments for nuclear fuel, coal and coal transportation. Power commitments consist of commitments for renewable energy under power purchase agreements. KCP&L and GMO purchase capacity from other utilities and nonutility suppliers. Purchasing capacity provides the option to purchase energy if needed or when market prices are favorable. KCP&L has capacity sales agreements not included above that total $5.5 million per year from 2015 to 2016, $1.3 million per year from 2017 to 2018 and $0.9 million for 2019. La Cygne environmental project represents 100% of the contractual commitments related to environmental upgrades at KCP&L's La Cygne Station. KCP&L owns 50% of the La Cygne Station and expects to be reimbursed by the other owner for its 50% share of the costs. Non-regulated natural gas transportation consists of MPS Merchant's commitments. Other represents individual commitments entered into in the ordinary course of business.

Legal_Proceedings

Legal Proceedings	12 Months Ended
	Dec. 31, 2014
Legal Proceedings [Abstract]
Legal Proceedings [Text Block]	16. 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.

Guarantees

Guarantees	12 Months Ended
	Dec. 31, 2014
Guarantees [Abstract]
Guarantees [Text Block]	17. GUARANTEES
	In the ordinary course of business, Great Plains Energy and certain of its subsidiaries enter into various agreements providing financial or performance assurance to third parties on behalf of certain subsidiaries. Such agreements include, for example, guarantees and letters of credit. These agreements are entered into primarily to support or enhance the creditworthiness otherwise attributed to a subsidiary on a stand-alone basis, thereby facilitating the extension of sufficient credit to accomplish the subsidiary's intended business purposes. The majority of these agreements guarantee the Company's own future performance, so a liability for the fair value of the obligation is not recorded.
	At December 31, 2014, Great Plains Energy has provided $139.5 million of credit support for GMO as follows:
	•	Great Plains Energy direct guarantees to GMO counterparties totaling $40.7 million, which expire in 2015 and 2016 and
	•	Great Plains Energy guarantee of GMO long-term debt totaling $98.8 million, which includes debt with maturity dates ranging from 2015 to 2023.
	Great Plains Energy has also guaranteed GMO's commercial paper program. At December 31, 2014, GMO had no commercial paper outstanding.

Related_Party_Transactions_and

Related Party Transactions and Relationships	12 Months Ended
	Dec. 31, 2014
Related Party Transactions [Abstract]
Related Party Transactions and Relationships	18. 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 $173.9 million for 2014, $223.6 million for 2013 and $207.9 million for 2012.  Additionally, KCP&L and GMO engage in wholesale electricity transactions with each other.  KCP&L's net wholesale sales to GMO were $12.7 million, $25.6 million and $29.4 million in 2014, 2013 and 2012, respectively.
	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, 2014 and 2013, KCP&L had a money pool payable to GMO of $12.6 million and $0.2 million, respectively. The following table summarizes KCP&L's related party net receivables.
		December 31
		2014		2013
		(millions)
	Net receivable from GMO	$	38.2	$	32.7
	Net receivable from Great Plains Energy	18		17.5

Derivative_Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	19. 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 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's 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 December 31, 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's 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's 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's 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 December 31, 2014, GMO had financial contracts in place to hedge approximately 32%, 15% and 9% of the expected on-peak natural gas generation and natural gas equivalent purchased power price exposure for 2015, 2016 and 2017, 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 mechanism.  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.
		December 31
		2014								2013
		Notional				Fair				Notional				Fair
		Contract				Value				Contract				Value
		Amount								Amount
	Great Plains Energy	(millions)
	Futures contracts
	Non-hedging derivatives	$	14.9			$	(2.4	)		$	19.3			$	(0.6	)
	Forward contracts
	Non-hedging derivatives	29.7				4.1				47.7				5.2
	Transmission congestion rights
	Non-hedging derivatives	28.3				2.6				22.9				1.7
	Option contracts
	Non-hedging derivatives	1.7				0.1				4.8				1.2
	KCP&L
	Futures contracts
	Non-hedging derivatives	$	—			$	—			$	7.7			$	(0.2	)
	Transmission congestion rights
	Non-hedging derivatives	23.6				3.1				18				1.1
	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
	December 31, 2014	Classification		Fair Value						Fair Value
	Derivatives Not Designated as Hedging Instruments				(millions)
	Commodity contracts	Other			$	8.6					$	4.2
	December 31, 2013
	Derivatives Not Designated as Hedging Instruments
	Commodity contracts	Other			$	8.5					$	1
	KCP&L
		Balance Sheet		Asset Derivatives						Liability Derivatives
	December 31, 2014	Classification		Fair Value						Fair Value
	Derivatives Not Designated as Hedging Instruments				(millions)
	Commodity contracts	Other			$	4					$	0.9
	December 31, 2013
	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			Net Amount
	31-Dec-14	(millions)
	Derivative assets		$	8.6					$	(1.2	)				$	7.4		$	—		$	—		$	7.4
	Derivative liabilities		4.2						(3.5		)				0.7			—			—			0.7
	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			Net Amount
	31-Dec-14	(millions)
	Derivative assets		$	4					$	(0.9	)				$	3.1		$	—		$	—		$	3.1
	Derivative liabilities		0.9						(0.9		)				—			—			—			—
	31-Dec-13
	Derivative assets		$	1.2					$	(0.1	)				$	1.1		$	—		$	—		$	1.1
Derivative liabilities		0.3						(0.3		)				—			—			—			—
At December 31, 2014 and 2013, Great Plains Energy offset $2.3 million and $0.2 million, respectively, of cash collateral posted with counterparties against net derivative positions.
See Note 21 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 December 31, 2014, includes $9.2 million that is expected to be reclassified to expenses over the next twelve months.  KCP&L's accumulated OCI at December 31, 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
Derivatives Not Designated as Hedging Instruments		2014				2013				2012
Location of Gain (Loss)		(millions)
Electric revenues		$	(14.2	)		$	—			$	—
Fuel		1.5				(1.1		)		(6.6		)
Purchased power		(4.9		)		—				—
Regulatory asset		(2.7		)		—				(3.7		)
Regulatory liability		—				0.2				—
Total		$	(20.3	)		$	(0.9	)		$	(10.3	)
KCP&L
Derivatives Not Designated as Hedging Instruments		2014				2013				2012
Location of Gain (Loss)		(millions)
Electric revenues		$	(14.2	)		$	—			$	—
Fuel		1.1				0.8				—
Regulatory asset		(0.2		)		—				—
Total		$	(13.3	)		$	0.8			$	—

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Measurements	20. 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 December 31, 2014, the book value and fair value of Great Plains Energy's long-term debt, including current maturities, were $3.5 billion and $3.8 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 December 31, 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.
	Description	December 31							Level 1		Level 2				Level 3
		2014
	KCP&L		(millions)
	Assets
	Nuclear decommissioning trust (a)
	Equity securities		$	137.1					$	137.1		$	—			$	—
	Debt securities
	U.S. Treasury		22.9						22.9			—				—
	U.S. Agency		3.5						—			3.5				—
	State and local obligations		4.1						—			4.1				—
	Corporate bonds		28.1						—			28.1				—
	Foreign governments		0.5						—			0.5				—
	Cash equivalents		2.3						2.3			—				—
	Other		0.5						—			0.5				—
	Total nuclear decommissioning trust		199						162.3			36.7				—
	Self-insured health plan trust (b)
	Equity securities		1.3						1.3			—				—
	Debt securities		7.6						—			7.6				—
	Cash and cash equivalents		6.2						6.2			—				—
	Total self-insured health plan trust		15.1						7.5			7.6				—
	Derivative instruments (c)		4						—			—				4
	Total		$	218.1					$	169.8		$	44.3			$	4
	Liabilities
	Derivative instruments (c)		0.9						—			—				0.9
	Total		$	0.9					$	—		$	—			$	0.9
	Other Great Plains Energy
	Assets
	Derivative instruments (c)		$	4.6					$	—		$	3.4			$	1.2
	SERP rabbi trusts (d)
	Equity securities		0.1						0.1			—				—
	Fixed income funds		17.8						—			17.8				—
	Total SERP rabbi trusts		17.9						0.1			17.8				—
	Total		22.5						0.1			21.2				1.2
	Liabilities
	Derivative instruments (c)		3.3						2.4			0.1				0.8
	Total		$	3.3					$	2.4		$	0.1			$	0.8
	Great Plains Energy
	Assets
	Nuclear decommissioning trust (a)		$	199					$	162.3		$	36.7			$	—
	Self-insured health plan trust (b)		15.1						7.5			7.6				—
	Derivative instruments (c)		8.6						—			3.4				5.2
	SERP rabbi trusts (d)		17.9						0.1			17.8				—
	Total		240.6						169.9			65.5				5.2
	Liabilities
	Derivative instruments (c)		4.2						2.4			0.1				1.7
	Total		$	4.2					$	2.4		$	0.1			$	1.7
	Description	December 31						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)		1.2						0.1			—				1.1
Total		$	199.9					$	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)		$	7.3					$	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		26						0.3			23.5				2.2
Liabilities
Derivative instruments (c)		0.7						0.6			0.1				—
Total		$	0.7					$	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)		8.5						0.3			4.9				3.3
SERP rabbi trusts (d)		18.7						0.1			18.6				—
Total		225.9						157.9			64.7				3.3
Liabilities
Derivative instruments (c)		1						0.9			0.1				—
Total		$	1					$	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 for equity securities and NAV per share for fixed income funds. The fixed income fund invests primarily in intermediate and long-term debt securities, can be redeemed immediately and is not subject to any restrictions on redemptions.
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 January 1	$	3.3			$	2.3
Total realized/unrealized gains (losses):
included in electric revenue	(14.2		)		—
included in purchased power expense	(4.9		)		—
included in non-operating income	14.6				9.5
included in regulatory asset	(0.1		)		—
Purchases	16				1.7
Settlements	(11.2		)		(10.2		)
Net asset at December 31	$	3.5			$	3.3
Total unrealized losses relating to assets still on the consolidated balance sheet at December 31:
included in electric revenue	$	(0.2	)		$	—
included in non-operating income	(0.3		)		(0.3		)
included in regulatory asset	(0.1		)		—
KCP&L
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Derivative Instruments
	2014				2013
	(millions)
Net asset at January 1	$	1.1			$	—
Total realized/unrealized gains (losses):
included in electric revenue	(14.2		)		—
included in regulatory asset	(0.2		)		—
Purchases	13.7				1.1
Settlements	2.7				—
Net asset at December 31	$	3.1			$	1.1
Total unrealized losses relating to assets still on the consolidated balance sheet at December 31:
included in electric revenue	$	(0.2	)		$	—
included in regulatory asset	(0.2		)		—

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss) [Text Block]	21. ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)
	The following tables reflect the change in the balances of each component of accumulated other comprehensive loss for Great Plains Energy and KCP&L.
	Great Plains Energy
		Gains and Losses on Cash Flow Hedges(a)						Defined Benefit Pension Items(a)				Total(a)
		(millions)
	2014
	Beginning balance January 1		$	(23.8	)				$	(1.5	)	$	(25.3	)
	Other comprehensive loss before reclassifications		—						(1.8		)	(1.8		)
	Amounts reclassified from accumulated other comprehensive loss		8						0.4			8.4
	Net current period other comprehensive income (loss)		8						(1.4		)	6.6
	Ending balance December 31		$	(15.8	)				$	(2.9	)	$	(18.7	)
	2013
	Beginning balance January 1		$	(35.4	)				$	(3.0	)	$	(38.4	)
	Other comprehensive income before reclassifications		—						1.2			1.2
	Amounts reclassified from accumulated other comprehensive loss		11.6						0.3			11.9
	Net current period other comprehensive income		11.6						1.5			13.1
	Ending balance December 31		$	(23.8	)				$	(1.5	)	$	(25.3	)
	(a) Net of tax
	KCP&L
		Gains and Losses on Cash Flow Hedges(a)
		(millions)
	2014
	Beginning balance January 1		$	(20.2	)
	Amounts reclassified from accumulated other comprehensive loss		5.3
	Net current period other comprehensive income		5.3
	Ending balance December 31		$	(14.9	)
	2013
	Beginning balance January 1		$	(25.8	)
	Amounts reclassified from accumulated other comprehensive loss		5.6
	Net current period other comprehensive income		5.6
	Ending balance December 31		$	(20.2	)
	(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
		2014				2013
		(millions)
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts	$	(13.1	)		$	(18.6	)		Interest charges
	Commodity contracts	—				(0.3		)		Fuel
		(13.1		)		(18.9		)		Income before income tax expense and loss from equity investments
		5.1				7.3				Income tax benefit
		$	(8.0	)		$	(11.6	)		Net income
	Amortization of defined benefit pension items
	Net losses included in net periodic benefit costs	$	(0.6	)		$	(0.5	)		Utility operating and maintenance expenses
		(0.6		)		(0.5		)		Income before income tax expense and loss from equity investments
		0.2				0.2				Income tax benefit
		$	(0.4	)		$	(0.3	)		Net income
	Total reclassifications, net of tax	$	(8.4	)		$	(11.9	)		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
		2014				2013
		(millions)
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts	$	(8.7	)		$	(8.8	)		Interest charges
	Commodity contracts	—				(0.3		)		Fuel
		(8.7		)		(9.1		)		Income before income tax expense
		3.4				3.5				Income tax benefit
	Total reclassifications, net of tax	$	(5.3	)		$	(5.6	)		Net income

Taxes

Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	22. TAXES
	Components of income tax expense are detailed in the following tables.
	Great Plains Energy	2014				2013				2012
	Current income taxes	(millions)
	Federal	$	0.4			$	0.3			$	(3.2	)
	State	(0.1		)		(3.0		)		(6.3		)
	Total	0.3				(2.7		)		(9.5		)
	Deferred income taxes
	Federal	104.2				109.1				96.3
	State	21.6				24.9				24.9
	Total	125.8				134				121.2
	Noncurrent income taxes
	Federal	(2.4		)		—				(0.2		)
	State	(0.5		)		(0.3		)		(0.3		)
	Foreign	(6.1		)		(0.4		)		(4.2		)
	Total	(9.0		)		(0.7		)		(4.7		)
	Investment tax credit
	Deferral	—				0.3				—
	Amortization	(1.4		)		(1.7		)		(2.4		)
	Total	(1.4		)		(1.4		)		(2.4		)
	Income tax expense	$	115.7			$	129.2			$	104.6
	KCP&L	2014				2013				2012
	Current income taxes	(millions)
	Federal	$	(9.4	)		$	(0.5	)		$	13.1
	State	(2.3		)		(0.5		)		2
	Total	(11.7		)		(1.0		)		15.1
	Deferred income taxes
	Federal	72.6				75.8				48.8
	State	15.8				16.3				11.4
	Total	88.4				92.1				60.2
	Noncurrent income taxes
	Federal	—				(9.0		)		1.7
	State	—				(1.5		)		0.1
	Total	—				(10.5		)		1.8
	Investment tax credit
	Deferral	—				0.3				—
	Amortization	(1.0		)		(1.1		)		(1.8		)
	Total	(1.0		)		(0.8		)		(1.8		)
	Income tax expense	$	75.7			$	79.8			$	75.3
	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.
	Great Plains Energy	2014			2013			2012
	Federal statutory income tax rate	35	%		35	%		35	%
	Differences between book and tax depreciation not normalized	(0.7	)		(0.3	)		1.2
	Amortization of investment tax credits	(0.4	)		(0.4	)		(0.8	)
	Federal income tax credits	(3.8	)		(3.5	)		(3.1	)
	State income taxes	3.8			3.8			4
	Changes in uncertain tax positions, net	(1.7	)		(0.2	)		(1.5	)
	Other	0.1			(0.4	)		(0.5	)
	Effective income tax rate	32.3	%		34	%		34.3	%
	KCP&L	2014			2013			2012
	Federal statutory income tax rate	35	%		35	%		35	%
	Differences between book and tax depreciation not normalized	(0.9	)		(0.8	)		1.3
	Amortization of investment tax credits	(0.4	)		(0.4	)		(0.8	)
	Federal income tax credits	(5.6	)		(5.3	)		(4.3	)
	State income taxes	3.7			3.7			4.1
	Other	—			(0.1	)		(0.6	)
	Effective income tax rate	31.8	%		32.1	%		34.7	%
	Deferred Income Taxes
	The tax effects of major temporary differences resulting in deferred income tax assets (liabilities) in the consolidated balance sheets are in the following tables.
			Great Plains Energy								KCP&L
	December 31		2014				2013				2014				2013
	Current deferred income tax asset (liability)		(millions)
	Net operating loss carryforward		$	62.2			$	76.6			$	—			$	—
Other		17.1				5.7				5				(1.7		)
Net current deferred income tax asset (liability) before valuation allowance		79.3				82.3				5				(1.7		)
Valuation allowance		(1.2		)		(2.0		)		—				—
Net current deferred income tax asset (liability)		78.1				80.3				5				(1.7		)
Noncurrent deferred income taxes
Plant related		(1,648.2		)		(1,433.8		)		(1,167.3		)		(1,022.9		)
Income taxes on future regulatory recoveries		(133.4		)		(136.4		)		(107.1		)		(111.0		)
Derivative instruments		26.5				32.3				18.9				23.4
Pension and post-retirement benefits		(14.0		)		(28.2		)		12.5				(1.7		)
SO2 emission allowance sales		27.1				28.8				27.3				28.8
Tax credit carryforwards		242.7				229.3				153.2				139.6
Customer demand programs		(26.2		)		(27.7		)		(19.0		)		(19.4		)
Solar rebates		(33.2		)		(17.5		)		(11.3		)		(5.1		)
Net operating loss carryforward		524.7				446.7				98.5				71.6
Other		(40.3		)		(39.6		)		(22.6		)		(25.4		)
Net noncurrent deferred income tax liability before valuation allowance		(1,074.3		)		(946.1		)		(1,016.9		)		(922.1		)
Valuation allowance		(15.4		)		(18.7		)		—				—
Net noncurrent deferred income tax liability		(1,089.7		)		(964.8		)		(1,016.9		)		(922.1		)
Net deferred income tax liability		$	(1,011.6	)		$	(884.5	)		$	(1,011.9	)		$	(923.8	)
		Great Plains Energy								KCP&L
December 31		2014				2013				2014				2013
		(millions)
Gross deferred income tax assets		$	1,227.00			$	1,148.20			$	624.8			$	583
Gross deferred income tax liabilities		(2,238.6		)		(2,032.7		)		(1,636.7		)		(1,506.8		)
Net deferred income tax liability		$	(1,011.6	)		$	(884.5	)		$	(1,011.9	)		$	(923.8	)
Tax Credit Carryforwards
At December 31, 2014 and 2013, Great Plains Energy had $155.1 million and $141.1 million, respectively, of federal general business income tax credit carryforwards.  At December 31, 2014 and 2013, KCP&L had $153.2 million and $139.6 million, respectively, of federal general business income tax credit carryforwards.  The carryforwards for both Great Plains Energy and KCP&L relate primarily to Advanced Coal Investment Tax Credits and Wind Production tax credits and expire in the years 2028 to 2034.  Approximately $0.5 million of Great Plains Energy's credits are related to Low Income Housing credits that were acquired in the GMO acquisition.  Due to federal limitations on the utilization of income tax attributes acquired in the GMO acquisition, management expects a portion of these credits to expire unutilized and has provided a valuation allowance against $0.4 million of the federal income tax benefit.
At December 31, 2014 and 2013, Great Plains Energy had $87.6 million and $87.9 million of federal alternative minimum tax credit carryforwards.  Of these amounts, $87.6 million, at December 31, 2014 and 2013, were acquired in the GMO acquisition.  These credits do not expire and can be used to reduce taxes paid in the future.
At December 31, 2014 and 2013, Great Plains Energy had none and $0.3 million, respectively, of state income tax credit carryforwards.  The state income tax credits related primarily to the Company's Missouri affordable housing investment portfolio.
Net Operating Loss Carryforwards
At December 31, 2014 and 2013, Great Plains Energy had $521.0 million and $459.9 million, respectively, of tax benefits related to federal net operating loss (NOL) carryforwards.  Approximately $313.2 million and $304.6 million, at December 31, 2014 and 2013, respectively, are tax benefits related to NOLs that were acquired in the GMO acquisition.  The tax benefits for NOLs originating in 2003 are $30.1 million, $152.4 million originating in 2004, $74.1 million originating in 2005, $53.3 million originating in 2006, $1.3 million originating in 2007, $2.4 million originating in 2008, $36.6 million originating in 2009, $5.0 million originating in 2010 and $109.5 million originating in 2011, $2.6 million originating in 2012, $3.2 million originating in 2013, and $50.5 million originating in 2014.  The federal NOL carryforwards expire in years 2023 to 2034.
In addition, Great Plains Energy also had deferred tax benefits of $65.9 million and $63.4 million related to state NOLs as of December 31, 2014 and 2013, respectively.  Of these amounts, approximately $40.7 million and $44.4 million at December 31, 2014 and 2013, respectively, were acquired in the GMO acquisition.  Management does not expect to utilize $16.2 million of NOLs in state tax jurisdictions where the Company does not expect to operate in the future.  Therefore, a valuation allowance has been provided against $16.2 million of state tax benefits.
Valuation Allowances
Great Plains Energy is required to assess the ultimate realization of deferred tax assets using a “more likely than not” assessment threshold.  This assessment takes into consideration tax planning strategies within Great Plains Energy's control.  As a result of this assessment, Great Plains Energy has established a partial valuation allowance for state tax NOL carryforwards, and tax credit carryforwards. During 2014 and 2013, $4.1 million and $3.1 million, respectively, of tax benefit was recorded in continuing operations primarily related to state NOL carryforwards offset by an increase in deferred tax expense since a portion of state NOLs expired at December 31, 2014 and 2013, respectively.
Uncertain Tax Positions
At December 31, 2014 and 2013, Great Plains Energy had $2.6 million and $9.8 million, respectively, of liabilities related to unrecognized tax benefits.  Of these amounts, $0.3 million and $6.5 million at December 31, 2014 and 2013, respectively, are expected to impact the effective tax rate if recognized.  The $7.2 million decrease in unrecognized tax benefits in 2014 is primarily due to a decrease of $6.1 million of unrecognized tax benefits related to former GMO non-regulated operations.
At December 31, 2012, Great Plains Energy had $21.4 million of liabilities related to unrecognized tax benefits of which $7.3 million was expected to impact the effective tax rate if recognized.  The $11.6 million decrease in unrecognized tax benefits is primarily due to a change in certain income tax accounting methods for the capitalization of assets at KCP&L. This reduction in unrecognized tax benefits is offset by an increase to deferred income tax liabilities since the unrecognized tax benefits were related to temporary tax differences.
At December 31, 2014 and 2013, KCP&L did not have liabilities related to unrecognized tax benefits. At December 31, 2012, KCP&L had $10.5 million of liabilities related to unrecognized tax benefits and none of this amount was expected to impact the effective rate if recognized. The $10.5 million decrease in unrecognized tax benefits in 2013 is primarily due to a change in certain income tax accounting methods for the capitalization of assets at KCP&L. This reduction in unrecognized tax benefits is offset by an increase to deferred income tax liabilities since the unrecognized tax benefits were related to temporary tax differences.
The following table reflects activity for Great Plains Energy and KCP&L related to the liability for unrecognized tax benefits.
	Great Plains Energy												KCP&L
	2014				2013				2012				2014				2013			2012
	(millions)
Beginning balance January 1	$	9.8			$	21.4			$	24			$	—			$	10.5		$	8.7
Additions for current year tax positions	—				—				3.7				—				—			3.6
Reductions for current year tax positions	(0.3		)		(0.3		)		—				—				—			—
Reductions for prior year tax positions	(6.9		)		(10.5		)		(1.8		)		—				(10.5		)	(1.6		)
Statute expirations	—				(0.3		)		(4.7		)		—				—			(0.2		)
Foreign currency translation adjustments	—				(0.5		)		0.2				—				—			—
Ending balance December 31	$	2.6			$	9.8			$	21.4			$	—			$	—		$	10.5
Great Plains Energy and KCP&L recognize interest related to unrecognized tax benefits in interest expense and penalties in non-operating expenses.  At December 31, 2014, 2013 and 2012, amounts accrued for interest related to unrecognized tax benefits for Great Plains Energy were none, $3.2 million and $3.5 million, respectively. At December 31, 2014, 2013 and 2012, amounts accrued for penalties with respect to unrecognized tax benefits for Great Plains Energy were none, $0.6 million and $0.7 million, respectively. In 2014, 2013 and 2012, Great Plains Energy recognized a decrease of $3.2 million, $0.1 million and $2.3 million, respectively, of interest expense related to unrecognized tax benefits.
The Company is unable to estimate the amount of unrecognized tax benefits for Great Plains Energy that may be recognized in the next twelve months.
Great Plains Energy files a consolidated federal income tax return as well as unitary and combined income tax returns in several state jurisdictions with Kansas and Missouri being the most significant.  The Company also files separate company returns in Canada and certain other states.

Segments_and_Related_Informati

Segments and Related Information	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Segments and Related Information	23. 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.
	2014	Electric				Other				Eliminations				Great Plains
		Utility												Energy
			(millions)
	Operating revenues		$	2,568.20			$	—			$	—			$	2,568.20
	Depreciation and amortization		(306.0		)		—				—				(306.0		)
	Interest (charges) income		(183.0		)		(41.2		)		35.7				(188.5		)
	Income tax (expense) benefit		(125.6		)		9.9				—				(115.7		)
	Net income (loss)		243.5				(0.7		)		—				242.8
	2013	Electric				Other				Eliminations				Great Plains
		Utility												Energy
			(millions)
	Operating revenues		$	2,446.30			$	—			$	—			$	2,446.30
	Depreciation and amortization		(289.7		)		—				—				(289.7		)
	Interest (charges) income		(190.5		)		(55.5		)		47.6				(198.4		)
	Income tax (expense) benefit		(135.4		)		6.2				—				(129.2		)
	Net income (loss)		257.1				(6.9		)		—				250.2
	2012	Electric				Other				Eliminations				Great Plains
		Utility												Energy
			(millions)
	Operating revenues		$	2,309.90			$	—			$	—			$	2,309.90
	Depreciation and amortization		(272.3		)		—				—				(272.3		)
	Interest (charges) income		(197.3		)		(67.3		)		43.8				(220.8		)
	Income tax (expense) benefit		(122.0		)		17.4				—				(104.6		)
	Net income (loss)		216.6				(16.7		)		—				199.9
		Electric				Other				Eliminations				Great Plains
		Utility												Energy
	2014		(millions)
	Assets		$	10,746.10			$	33.1			$	(303.5	)		$	10,475.70
	Capital expenditures		773.7				—				—				773.7
	2013
	Assets		$	10,019.60			$	105.6			$	(329.8	)		$	9,795.40
	Capital expenditures		669				—				—				669
	2012
	Assets		$	9,910.60			$	122.4			$	(385.7	)		$	9,647.30
	Capital expenditures		610.2				—				—				610.2

Jointly_Owned_Electric_Utility

Jointly Owned Electric Utility Plants	12 Months Ended
	Dec. 31, 2014
Jointly Owned Electric Utility Plants [Abstract]
Jointly Owned Electric Utility Plants [Text Block]	24. JOINTLY-OWNED ELECTRIC UTILITY PLANTS
	Great Plains Energy's and KCP&L's share of jointly-owned electric utility plants at December 31, 2014, are detailed in the following tables.
	Great Plains Energy
		Wolf Creek Unit			La Cygne Units			Iatan No. 1 Unit			Iatan No. 2 Unit			Iatan Common			Jeffrey Energy Center
		(millions, except MW amounts)
	Great Plains Energy's share		47%			50%			88%			73%			79%			8%
	Utility plant in service		$	1,745.60		$	562.6		$	645.8		$	1,318.30		$	441.2		$	172.7
	Accumulated depreciation		832.4			320.4			261.8			342			99			77.3
	Nuclear fuel, net		79.2			—			—			—			—			—
	Construction work in progress		74.6			533.9			19.3			16.6			18.6			19.9
	2015 accredited capacity-MWs		549			696			627			641			NA			172
	KCP&L
		Wolf Creek Unit			La Cygne Units			Iatan No. 1 Unit			Iatan No. 2 Unit			Iatan Common
		(millions, except MW amounts)
	KCP&L's share		47%			50%			70%			55%			61%
	Utility plant in service		$	1,745.60		$	562.6		$	515.4		$	1,006.80		$	357.8
	Accumulated depreciation		832.4			320.4			211.4			313.9			89.2
	Nuclear fuel, net		79.2			—			—			—			—
	Construction work in progress		74.6			533.9			5.4			7.8			2.4
	2015 accredited capacity-MWs		549			696			499			482			NA
	Each owner must fund its own portion of the plant's operating expenses and capital expenditures. KCP&L's and GMO's share of direct expenses are included in the appropriate operating expense classifications in Great Plains Energy's and KCP&L's financial statements.

Quarterly_Operating_Results_Un

Quarterly Operating Results (Unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Text Block]	25. QUARTERLY OPERATING RESULTS (UNAUDITED)
		Quarter
	Great Plains Energy	1st		2nd		3rd		4th
	2014	(millions, except per share amounts)
	Operating revenue	$	585.1	$	648.4	$	782.5	$	552.2
	Operating income	77.9		124.2		263.2		69.2
	Net income	23.8		52.1		147.4		19.5
	Basic earnings per common share	0.15		0.34		0.96		0.12
	Diluted earnings per common share	0.15		0.34		0.95		0.12
	2013
	Operating revenue	$	542.2	$	600.3	$	765	$	538.8
	Operating income	86.1		143.6		271.7		67.8
	Net income	26		63.6		143.1		17.5
	Basic and diluted earnings per common share	0.17		0.41		0.93		0.11
		Quarter
	KCP&L	1st		2nd		3rd		4th
	2014	(millions)
	Operating revenue	$	391	$	439.5	$	533.4	$	366.9
	Operating income	47.5		78.2		177.2		47.2
	Net income	17.2		34.8		94.5		15.9
	2013
	Operating revenue	$	366.7	$	410.8	$	522	$	371.9
	Operating income	52.3		93.4		176.8		40
	Net income	16.2		44.2		96.4		12.2
	Quarterly data is subject to seasonal fluctuations with peak periods occurring in the summer months.

Schedule_I_Financial_Statement

Schedule I Financial Statements of Parent Company	12 Months Ended
	Dec. 31, 2014
Condensed Financial Information of Parent Company Only Disclosure [Text Block]	GREAT PLAINS ENERGY INCORPORATED
	NOTES TO FINANCIAL STATEMENTS OF PARENT COMPANY
	The Great Plains Energy Incorporated Notes to Consolidated Financial Statements in Part II, Item 8 should be read in conjunction with the Great Plains Energy Incorporated Parent Company Financial Statements.
	The Great Plains Energy Incorporated Parent Company Financial Statements have been prepared to present the financial position, results of operations and cash flows of Great Plains Energy on a stand-alone basis as a holding company. Investments in subsidiaries are accounted for using the equity method.

Schedule_II_Valuation_and_Qual

Schedule II Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2014
Valuation and Qualifying Accounts [Abstract]
Schedule II Valuation and Qualifying Accounts
	Great Plains Energy Incorporated
	Valuation and Qualifying Accounts
	Years Ended December 31, 2014, 2013 and 2012
					Additions
					Charged
		Balance At			To Costs				Charged								Balance
		Beginning			And				To Other								At End
	Description	Of Period			Expenses				Accounts				Deductions				Of Period
	Year Ended December 31, 2014	(millions)
	Allowance for uncollectible accounts		$	2.5		$	11.4			$	8.5	(a)		$	19.6	(b)		$	2.8
	Legal reserves		4.6			2.7				—				2.6		(c)		4.7
	Environmental reserves		1.7			—				—				—				1.7
	Tax valuation allowance		20.7			0.5				—				4.6		(d)		16.6
	Year Ended December 31, 2013
	Allowance for uncollectible accounts		$	6.9		$	12.3			$	7.6	(a)		$	24.3	(b)		$	2.5
	Legal reserves		4.6			2.7				—				2.7		(c)		4.6
	Environmental reserves		2.3			—				—				0.6				1.7
	Tax valuation allowance		23.8			0.1				—				3.2		(d)		20.7
	Year Ended December 31, 2012
	Allowance for uncollectible accounts		$	6.8		$	12			$	7.8	(a)		$	19.7	(b)		$	6.9
	Legal reserves		6.7			(0.2		)		—				1.9		(c)		4.6
	Environmental reserves		2.5			—				—				0.2				2.3
	Tax valuation allowance		23.9			0.3				—				0.4		(d)		23.8
	(a)    Recoveries.
	(b)    Uncollectible accounts charged off.
	(c)    Payment of claims.
	(d)    Reversal of tax valuation allowance.
	Kansas City Power & Light Company
	Valuation and Qualifying Accounts
	Years Ended December 31, 2014, 2013 and 2012
					Additions
					Charged
		Balance At			To Costs				Charged								Balance
		Beginning			And				To Other								At End
	Description	Of Period			Expenses				Accounts				Deductions				Of Period
	Year Ended December 31, 2014	(millions)
	Allowance for uncollectible accounts		$	1.1		$	7.6			$	5.5	(a)		$	13	(b)		$	1.2
	Legal reserves		2.9			2.3				—				2.3		(c)		2.9
	Environmental reserves		0.3			—				—				—				0.3
	Year Ended December 31, 2013
	Allowance for uncollectible accounts		$	1.5		$	8			$	5	(a)		$	13.4	(b)		$	1.1
	Legal reserves		2.9			0.9				—				0.9		(c)		2.9
	Environmental reserves		0.3			—				—				—				0.3
	Year Ended December 31, 2012
	Allowance for uncollectible accounts		$	1.4		$	7.9			$	5.2	(a)		$	13	(b)		$	1.5
	Legal reserves		3.9			0.5				—				1.5		(c)		2.9
	Environmental reserves		0.3			—				—				—				0.3
	(a)    Recoveries.
	(b)    Uncollectible accounts charged off.
	(c)    Payment of claims.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 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 23 for additional information.
Use of Estimates, Policy [Policy Text Block]	Use of Estimates
	The process of preparing financial statements in conformity with Generally Accepted Accounting Principles (GAAP) requires the use of estimates and assumptions that affect the reported amounts of certain types of assets, liabilities, revenues and expenses. Such estimates primarily relate to unsettled transactions and events as of the date of the financial statements. Accordingly, upon settlement, actual results may differ from estimated amounts.
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash and Cash Equivalents
	Cash equivalents consist of highly liquid investments with original maturities of three months or less at acquisition.
Funds on Deposit, Policy [Policy Text Block]	Funds on Deposit
	Funds on deposit consist primarily of cash provided to counterparties in support of margin requirements related to commodity purchases, commodity swaps and futures contracts. Pursuant to individual contract terms with counterparties, deposit amounts required vary with changes in market prices, credit provisions and various other factors. Interest is earned on most funds on deposit. Great Plains Energy also holds funds on deposit from counterparties in the same manner. These funds are included in other current liabilities on the consolidated balance sheets.
Fair Value of Financial Instruments, Policy [Policy Text Block]	Fair Value of Financial Instruments
	The following methods and assumptions were used to estimate the fair value of each class of financial instrument for which it is practicable to estimate that value.
	Nuclear decommissioning trust fund - KCP&L's nuclear decommissioning trust fund assets are recorded at fair value based on quoted market prices of the investments held by the fund and/or valuation models.
	Derivative instruments - The fair value of derivative instruments is estimated using market quotes, over-the-counter forward price and volatility curves and correlation among fuel prices, net of estimated credit risk.
	Pension plans - For financial reporting purposes, the market value of plan assets is the fair value. For regulatory reporting purposes, a five-year smoothing of assets is used to determine fair value.
Derivatives, Policy [Policy Text Block]	Derivative Instruments
	The Company records derivative instruments on the balance sheet at fair value in accordance with GAAP. Great Plains Energy and KCP&L enter into derivative contracts to manage exposure to commodity price and interest rate fluctuations. Derivative instruments are used solely for hedging purposes and are not issued or held for speculative reasons.
	The Company considers various qualitative factors, such as contract and market place attributes, in designating derivative instruments at inception. Great Plains Energy and KCP&L may elect the normal purchases and normal sales (NPNS) exception, which requires the effects of the derivative to be recorded when the underlying contract settles. Great Plains Energy and KCP&L account for derivative instruments that are not designated as NPNS as cash flow hedges or non-hedging derivatives, which are recorded as assets or liabilities on the consolidated balance sheets at fair value. In addition, if a derivative instrument is designated as a cash flow hedge, Great Plains Energy and KCP&L document the method of determining hedge effectiveness and measuring ineffectiveness. See Note 19 for additional information regarding derivative financial instruments and hedging activities.
	Great Plains Energy and KCP&L offset fair value amounts recognized for derivative instruments under master netting arrangements, which include rights to reclaim cash collateral (a receivable), or the obligation to return cash collateral (a payable). Great Plains Energy and KCP&L classify cash flows from derivative instruments accounted for as a cash flow hedge in the same category as the cash flows from the items being hedged.
Utility Plant, Policy [Policy Text Block]	Utility Plant
	Great Plains Energy's and KCP&L's utility plant is stated at historical cost. These costs include taxes, an allowance for the cost of borrowed and equity funds used to finance construction and payroll-related costs, including pensions and other fringe benefits. Replacements, improvements and additions to units of property are capitalized. Repairs of property and replacements of items not considered to be units of property are expensed as incurred (except as discussed under Deferred Refueling Outage Costs). When property units are retired or otherwise disposed, the original cost, net of salvage, is charged to accumulated depreciation. Substantially all of KCP&L's utility plant is pledged as collateral for KCP&L's mortgage bonds under the General Mortgage Indenture and Deed of Trust dated December 1, 1986, as supplemented. Substantially all of GMO's St. Joseph Light & Power division utility plant is pledged as collateral for GMO's mortgage bonds under the General Mortgage Indenture and Deed of Trust dated April 1, 1946, as supplemented.
	As prescribed by The Federal Energy Regulatory Commission (FERC), Allowance for Funds Used During Construction (AFUDC) is charged to the cost of the plant during construction. AFUDC equity funds are included as a non-cash item in non-operating income and AFUDC borrowed funds are a reduction of interest charges. The rates used to compute gross AFUDC are compounded semi-annually and averaged 5.7% in 2014, 6.1% in 2013 and 2.0% in 2012 for KCP&L. The rates used to compute gross AFUDC for GMO averaged 6.1% in 2014, 2.1% in 2013 and 2.4% in 2012.
	Great Plains Energy's and KCP&L's balances of utility plant, at original cost, with a range of estimated useful lives are listed in the following tables.
	Great Plains Energy
	December 31		2014				2013
	Utility plant, at original cost		(millions)
	Generation (20 - 60 years)		$	7,169.60			$	6,874.60
	Transmission (15 - 70 years)		821.9				794
	Distribution (8 - 66 years)		3,311.60				3,149.40
	General (5 - 50 years)		825.6				757.3
	Total (a)		$	12,128.70			$	11,575.30
	(a) Includes $127.9 million and $107.8 million at December 31, 2014 and 2013, respectively, of land and other assets that are not depreciated.
	KCP&L
	December 31		2014				2013
	Utility plant, at original cost		(millions)
	Generation (20 - 60 years)		$	5,554.30			$	5,288.30
	Transmission (15 - 70 years)		448.9				433.7
	Distribution (8 - 55 years)		2,089.00				1,970.20
	General (5 - 50 years)		645.1				582.7
	Total (a)		$	8,737.30			$	8,274.90
	(a) Includes $72.4 million and $54.1 million at December 31, 2014 and 2013, respectively, of land and other assets that are not depreciated.
Depreciation and Amortization, Policy [Policy Text Block]	Depreciation and Amortization
	Depreciation and amortization of utility plant other than nuclear fuel is computed using the straight-line method over the estimated lives of depreciable property based on rates approved by state regulatory authorities. Annual depreciation rates average approximately 3%. Nuclear fuel is amortized to fuel expense based on the quantity of heat produced during the generation of electricity.
Nuclear Plant Decommissioning Costs, Policy [Policy Text Block]	Nuclear Plant Decommissioning Costs
	Nuclear plant decommissioning cost estimates are based on the immediate dismantlement method and include the costs of decontamination, dismantlement and site restoration. Based on these cost estimates, KCP&L contributes to a tax-qualified trust fund to be used to decommission Wolf Creek Generating Station (Wolf Creek). Related liabilities for decommissioning are included on Great Plains Energy's and KCP&L's balance sheets in Asset Retirement Obligations (AROs).
	As a result of the authorized regulatory treatment and related regulatory accounting, differences between the decommissioning trust fund asset and the related ARO are recorded as a regulatory asset or liability. See Note 7 for discussion of AROs including those associated with nuclear plant decommissioning costs.
Deferred Refueling Outage Costs, Policy [Policy Text Block]	Deferred Refueling Outage Costs
	KCP&L uses the deferral method to account for operations and maintenance expenses incurred in support of Wolf Creek's scheduled refueling outages and amortizes them evenly (monthly) over the unit's operating cycle, which is approximately 18 months, until the next scheduled outage. Replacement power costs during an outage are expensed as incurred.
Regulatory Matters, Policy [Policy Text Block]	Regulatory Matters
	KCP&L and GMO defer items on the balance sheet resulting from the effects of the ratemaking process, which would not be recorded if KCP&L and GMO were not regulated. See Note 5 for additional information concerning regulatory matters.
Revenue Recognition, Policy [Policy Text Block]	Revenue Recognition
	Great Plains Energy and KCP&L recognize revenues on sales of electricity when the service is provided. Revenues recorded include electric services provided but not yet billed by KCP&L and GMO. Unbilled revenues are recorded for kWh usage in the period following the customers' billing cycle to the end of the month. KCP&L's and GMO's estimate is based on net system kWh usage less actual billed kWhs. KCP&L's and GMO's estimated unbilled kWhs are allocated and priced by regulatory jurisdiction across the rate classes based on actual billing rates.
	KCP&L and GMO collect from customers gross receipts taxes levied by state and local governments. These taxes from KCP&L's Missouri customers are recorded gross in operating revenues and general taxes on Great Plains Energy's and KCP&L's statements of income. KCP&L's gross receipts taxes collected from Missouri customers were $60.4 million, $58.9 million and $55.8 million in 2014, 2013 and 2012, respectively. These taxes from KCP&L's Kansas customers and GMO's customers are recorded net in operating revenues on Great Plains Energy's and KCP&L's statements of income.
	Great Plains Energy and KCP&L collect sales taxes from customers and remit to state and local governments. These taxes are presented on a net basis on Great Plains Energy's and KCP&L's statements of income.
	Great Plains Energy and KCP&L record sale and purchase activity on a net basis in wholesale revenue or purchased power when transacting with Regional Transmission Organization (RTO)/Independent System Operator (ISO) markets.
Allowance for Doubtful Accounts, Policy [Policy Text Block]	Allowance for Doubtful Accounts
	This reserve represents estimated uncollectible accounts receivable and is based on management's judgment considering historical loss experience and the characteristics of existing accounts. Provisions for losses on receivables are expensed to maintain the allowance at a level considered adequate to cover expected losses. Receivables are charged off against the reserve when they are deemed uncollectible.
Property Gains And Losses, Policy [Policy Text Block]	Property Gains and Losses
	Net gains and losses from the sale of assets and businesses and from asset impairments are recorded in operating expenses.
Asset Impairments, Policy [Policy Text Block]	Asset Impairments
	Long-lived assets and finite-lived intangible assets subject to amortization are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. If the sum of the undiscounted expected future cash flows from an asset to be held and used is less than the carrying value of the asset, an asset impairment must be recognized in the financial statements. The amount of impairment recognized is the excess of the carrying value of the asset over its fair value.
	Goodwill and indefinite lived intangible assets are tested for impairment annually and when an event occurs indicating the possibility that an impairment exists. The annual test must be performed at the same time each year. If the fair value of a reporting unit is less than its carrying value including goodwill, an impairment charge for goodwill must be recognized in the financial statements. To measure the amount of the impairment loss to recognize, the implied fair value of the reporting unit goodwill is compared with its carrying value.
Income Taxes, Policy [Policy Text Block]	Income Taxes
	Income taxes are accounted for using the asset/liability approach. Deferred tax assets and liabilities are determined based on the temporary differences between the financial reporting and tax bases of assets and liabilities, applying enacted statutory tax rates in effect for the year in which the differences are expected to reverse. Deferred tax assets are reduced by a valuation allowance when, in the opinion of management, it is more likely than not that some portion of the deferred tax assets will not be realized.
	Great Plains Energy and KCP&L recognize tax benefits based on a “more-likely-than-not” recognition threshold. In addition, Great Plains Energy and KCP&L recognize interest accrued related to unrecognized tax benefits in interest expense and penalties in non-operating expenses.
	Great Plains Energy files a consolidated federal income tax return as well as unitary and combined income tax returns in several state jurisdictions with Kansas and Missouri being the most significant. Income taxes for consolidated or combined subsidiaries are allocated to the subsidiaries based on separate company computations of income or loss. KCP&L's income tax provision includes taxes allocated based on its separate company income or loss.
	Great Plains Energy and KCP&L have established a net regulatory asset for the additional future revenues to be collected from customers for deferred income taxes. Tax credits are recognized in the year generated except for certain KCP&L and GMO investment tax credits that have been deferred and amortized over the remaining service lives of the related properties.
Environmental Matters, Policy [Policy Text Block]	Environmental Matters
	Environmental costs are accrued when it is probable a liability has been incurred and the amount of the liability can be reasonably estimated.
Basic and Diluted Earnings per Common Share Calculation [Policy Text Block]	Basic and Diluted Earnings per Common Share Calculation
	To determine basic earnings per common share (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, restricted stock and Equity Units. Great Plains Energy settled the Equity Units in June 2012.
	The following table reconciles Great Plains Energy's basic and diluted EPS.
		2014				2013			2012
	Income	(millions, except per share amounts)
	Net income	$	242.8			$	250.2		$	199.9
	Less: preferred stock dividend requirements	1.6				1.6			1.6
	Earnings available for common shareholders	$	241.2			$	248.6		$	198.3
	Common Shares Outstanding
	Average number of common shares outstanding	153.9				153.5			145.5
	Add: effect of dilutive securities	0.2				0.2			1.7
	Diluted average number of common shares outstanding	154.1				153.7			147.2
	Basic EPS	$	1.57			$	1.62		$	1.36
	Diluted EPS	$	1.57			$	1.62		$	1.35
	Anti-dilutive shares excluded from the computation of diluted EPS are detailed in the following table.
		2014			2013			2012
	Performance shares	482,987			548,242			—
	Restricted stock shares	3,287			2,228			3,781
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 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)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Schedule of Public Utility Property, Plant, and Equipment [Table Text Block]	Great Plains Energy's and KCP&L's balances of utility plant, at original cost, with a range of estimated useful lives are listed in the following tables.
	Great Plains Energy
	December 31		2014				2013
	Utility plant, at original cost		(millions)
	Generation (20 - 60 years)		$	7,169.60			$	6,874.60
	Transmission (15 - 70 years)		821.9				794
	Distribution (8 - 66 years)		3,311.60				3,149.40
	General (5 - 50 years)		825.6				757.3
	Total (a)		$	12,128.70			$	11,575.30
	(a) Includes $127.9 million and $107.8 million at December 31, 2014 and 2013, respectively, of land and other assets that are not depreciated.
	KCP&L
	December 31		2014				2013
	Utility plant, at original cost		(millions)
	Generation (20 - 60 years)		$	5,554.30			$	5,288.30
	Transmission (15 - 70 years)		448.9				433.7
	Distribution (8 - 55 years)		2,089.00				1,970.20
	General (5 - 50 years)		645.1				582.7
	Total (a)		$	8,737.30			$	8,274.90
	(a) Includes $72.4 million and $54.1 million at December 31, 2014 and 2013, respectively, of land and other assets that are not depreciated.
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	The following table reconciles Great Plains Energy's basic and diluted EPS.
		2014				2013			2012
	Income	(millions, except per share amounts)
	Net income	$	242.8			$	250.2		$	199.9
	Less: preferred stock dividend requirements	1.6				1.6			1.6
	Earnings available for common shareholders	$	241.2			$	248.6		$	198.3
	Common Shares Outstanding
	Average number of common shares outstanding	153.9				153.5			145.5
	Add: effect of dilutive securities	0.2				0.2			1.7
	Diluted average number of common shares outstanding	154.1				153.7			147.2
	Basic EPS	$	1.57			$	1.62		$	1.36
	Diluted EPS	$	1.57			$	1.62		$	1.35
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.
		2014			2013			2012
	Performance shares	482,987			548,242			—
	Restricted stock shares	3,287			2,228			3,781

Supplemental_Cash_Flow_Informa1

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2014
Supplemental Cash Flow Elements [Abstract]
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]
	Great Plains Energy Other Operating Activities
	Year Ended December 31	2014			2013			2012
	Cash flows affected by changes in:	(millions)
	Receivables	$	3		$	(7.1	)	$	76.8
	Accounts receivable pledged as collateral	4			(1.0		)	(79.0		)
	Fuel inventories	(13.7		)	18.7			(6.1		)
	Materials and supplies	(0.4		)	(1.0		)	(11.0		)
	Accounts payable	15.2			26.4			57.3
	Accrued taxes	8.3			2.2			(7.8		)
	Accrued interest	(4.1		)	3.9			(35.2		)
	Deferred refueling outage costs	17			(17.6		)	15.6
	Pension and post-retirement benefit obligations	25.5			31.3			14.4
	Allowance for equity funds used during construction	(18.0		)	(14.1		)	(1.3		)
	Fuel recovery mechanism	(28.5		)	(1.3		)	22.5
	Solar rebates paid	(43.2		)	(32.5		)	(15.9		)
	Uncertain tax positions	(9.0		)	(0.8		)	(4.7		)
	Other	(3.3		)	17			(13.9		)
	Total other operating activities	$	(47.2	)	$	24.1		$	11.7
	Cash paid during the period:
	Interest	$	174.8		$	170.8		$	247.9
	Income taxes	$	—		$	—		$	3.3
	Non-cash investing activities:
	Liabilities accrued for capital expenditures	$	57.4		$	48.1		$	57.5
	KCP&L Other Operating Activities
	Year Ended December 31	2014			2013			2012
	Cash flows affected by changes in:	(millions)
	Receivables	$	(18.1	)	$	(12.6	)	$	8.8
	Accounts receivable pledged as collateral	—			—			(15.0		)
	Fuel inventories	(8.5		)	13.3			(4.6		)
	Materials and supplies	(1.1		)	1.1			(9.0		)
	Accounts payable	20.4			7.3			48.3
	Accrued taxes	(42.5		)	(3.7		)	(2.0		)
	Accrued interest	(0.1		)	1.4			(2.3		)
	Deferred refueling outage costs	17			(17.6		)	15.6
	Pension and post-retirement benefit obligations	26.9			35.7			18
	Allowance for equity funds used during construction	(16.0		)	(14.1		)	(1.3		)
	Fuel recovery mechanism	(2.2		)	(1.8		)	5.1
	Solar rebates paid	(17.3		)	(8.2		)	(5.8		)
	Uncertain tax positions	—			(10.5		)	1.8
	Other	(23.2		)	0.5			(29.7		)
	Total other operating activities	$	(64.7	)	$	(9.2	)	$	27.9
	Cash paid during the period:
	Interest	$	112.1		$	111.7		$	118
	Income taxes	$	30.2		$	4.6		$	18
	Non-cash investing activities:
	Liabilities accrued for capital expenditures	$	48.8		$	40.5		$	48.4

Receivables_Tables

Receivables (Tables)	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Schedule of receivables [Table Text Block]	Great Plains Energy's and KCP&L's receivables are detailed in the following table.
		December 31
		2014				2013
	Great Plains Energy	(millions)
	Customer accounts receivable - billed	$	1.1			$	1.5
	Customer accounts receivable - unbilled	75.3				74.6
	Allowance for doubtful accounts - customer accounts receivable	(2.8		)		(2.5		)
	Other receivables	86.7				88.6
	Total	$	160.3			$	162.2
	KCP&L
	Customer accounts receivable - billed	$	0.6			$	1.3
	Customer accounts receivable - unbilled	49.7				51.2
	Allowance for doubtful accounts - customer accounts receivable	(1.2		)		(1.1		)
	Other receivables	79.8				77.8
	Total	$	128.9			$	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.
	2014	KCP&L						KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
								Receivables				KCP&L								Receivables
								Company												Company
		(millions)
	Receivables (sold) purchased		$	(1,595.8	)				$	1,595.80			$	—			$	(816.3	)		$	816.3			$	—
	Gain (loss) on sale of accounts receivable (a)		(20.2		)				20.2				—				(10.3		)		10.4				0.1
	Servicing fees received (paid)		2.6						(2.6		)		—				1.2				(1.2		)		—
	Fees paid to outside investor		—						(1.1		)		(1.1		)		—				(0.6		)		(1.7		)
	Cash from customers (transferred) received		(1,608.3		)				1,608.30				—				(823.5		)		823.5				—
	Cash received from (paid for) receivables purchased		1,588.10						(1,588.1		)		—				813.1				(813.1		)		—
	Interest on intercompany note received (paid)		0.3						(0.3		)		—				0.1				(0.1		)		—
	2013	KCP&L						KCP&L				Consolidated				GMO				GMO				Consolidated Great Plains Energy
								Receivables				KCP&L								Receivables
								Company												Company
		(millions)
	Receivables (sold) purchased		$	(1,517.2	)				$	1,517.20			$	—			$	(834.7	)		$	834.7			$	—
	Gain (loss) on sale of accounts receivable (a)		(19.2		)				19.1				(0.1		)		(10.6		)		10.5				(0.2		)
	Servicing fees received (paid)		2.6						(2.6		)		—				1.4				(1.4		)		—
	Fees paid to outside investor		—						(1.2		)		(1.2		)		—				(0.7		)		(1.9		)
	Cash from customers (transferred) received		(1,516.2		)				1,516.20				—				(830.9		)		830.9				—
	Cash received from (paid for) receivables purchased		1,497.20						(1,497.2		)		—				820.5				(820.5		)		—
	Interest on intercompany note received (paid)		0.3						(0.3		)		—				0.1				(0.1		)		—
	(a) Any net gain (loss) is the result of the timing difference inherent in collecting receivables and over the life of the agreement will net to zero.

Nuclear_Plant_Tables

Nuclear Plant (Tables)	12 Months Ended
	Dec. 31, 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.
		2014					2013
	Decommissioning Trust		(millions)
	Beginning balance January 1		$	183.9				$	154.7
	Contributions		3.3					3.3
	Earned income, net of fees		3.6					2.7
	Net realized gains		0.4					1.7
	Net unrealized gains		7.8					21.5
	Ending balance December 31		$	199				$	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.
		December 31
		2014																	2013
		Cost			Unrealized Gains						Unrealized				Fair			Cost			Unrealized			Unrealized				Fair
		Basis									Losses				Value			Basis			Gains			Losses				Value
		(millions)
	Equity securities	$	87.2			$	50.6					$	(0.7	)		$	137.1		$	83.7		$	44.6		$	(0.6	)		$	127.7
	Debt securities	55.4				3.8						(0.1		)		59.1			51			2.5			(0.7		)		52.8
	Other	2.8				—						—				2.8			3.4			—			—				3.4
	Total	$	145.4			$	54.4					$	(0.8	)		$	199		$	138.1		$	47.1		$	(1.3	)		$	183.9
Gains and losses from the sale of securities by the nuclear decommissioning trust fund	The following table summarizes the realized gains and losses from the sale of securities in the nuclear decommissioning trust fund.
		2014			2013				2012
		(millions)
	Realized gains	$	1.4		$	2.4			$	1.7
	Realized losses	(1.0		)	(0.7		)		(0.7		)
Nuclear plant decommissioning costs [Table Text Block]
			KCC			MPSC
		(millions)
	Current cost of decommissioning (in 2014 dollars)
	Total Station		$	765.1		$	765.1
	KCP&L's 47% Share		359.6			359.6
	Future cost of decommissioning (in 2045-2053 dollars) (a)
	Total Station		$	2,201.50		$	2,253.10
	KCP&L's 47% Share		1,034.70			1,059.00
	Annual escalation factor		3.15%			3.22%
	Annual return on trust assets (b)		6.15%			5.68%
	(a) Total future cost over an eight year decommissioning period
	(b) The 6.15% and 5.68% rate of return for KCC and MPSC, respectively, is through 2025. The rates then systematically decrease through 2053 to 0.72% and 2.22% for KCC and MPSC, respectively, based on the assumption that the fund's investment mix will become increasingly conservative as the decommissioning period approaches.

Regulatory_Matters_Tables

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2014
Regulated Operations [Abstract]
Schedule Of Regulatory Assets And Liabilities [Table Text Block]	Great Plains Energy's and KCP&L's regulatory assets and liabilities are detailed in the following table.
		December 31
		2014								2013
		KCP&L			GMO			Great Plains Energy		KCP&L		GMO		Great Plains Energy
	Regulatory Assets	(millions)
	Taxes recoverable through future rates	$	107.1		$	26.3		$	133.4	$	111	$	25.4	$	136.4
	Loss on reacquired debt	8.1		(a)	2.8		(a)	10.9		7.1		1.5		8.6
	Cost of removal	2.8			—			2.8		1		—		1
	Asset retirement obligations	38.1			17.2			55.3		34.8		16		50.8
	Pension and post-retirement costs	430.5		(b)	95.4		(b)	525.9		310		91.2		401.2
	Deferred customer programs	50.8		(c)	18.8		(d)	69.6		50.2		21.8		72
	Rate case expenses	1.4		(e)	0.1			1.5		3.6		0.6		4.2
	Fuel recovery mechanism	13		(e)	41		(e)	54		10.8		12.8		23.6
	Acquisition transition costs	7		(f)	6.6		(f)	13.6		12.9		11		23.9
	Derivative instruments	0.2		(g)	2.6		(g)	2.8		—		—		—
	Iatan No. 1 and common facilities depreciation and carrying costs	14.7		(h)	5.5		(h)	20.2		15.3		5.7		21
	Iatan No. 2 construction accounting costs	28.1		(i)	15.3		(i)	43.4		29.3		16		45.3
	Kansas property tax surcharge	6.1		(e)	—			6.1		4		—		4
	Solar rebates	29.1		(e)	56.9		(e)	86		13		32.3		45.3
	Voluntary separation program	2.5		(j)	—			2.5		3.4		—		3.4
	Other	6.2		(e)	0.4		(e)	6.6		7.7		1.3		9
	Total	$	745.7		$	288.9		$	1,034.60	$	614.1	$	235.6	$	849.7
	Regulatory Liabilities
	Emission allowances	$	70.1		$	—		$	70.1	$	74	$	—	$	74
	Asset retirement obligations	93.9			—			93.9		86.2		—		86.2
	Cost of removal	—			69.7		(k)	69.7		—		68.1		68.1
	Other	8			41			49		8.1		27.6		35.7
	Total	$	172		$	110.7		$	282.7	$	168.3	$	95.7	$	264
	(a) Amortized over the life of the related new debt issuances or the remaining lives of the old debt issuances if no new debt was issued.
	(b) Represents unrecognized gains and losses, prior service and transition costs that will be recognized in future net periodic pension and post-retirement costs, pension settlements amortized over various periods and financial and regulatory accounting method differences that will be eliminated over the life of the pension plans. Of these amounts, $408.1 million and $55.7 million for KCP&L and GMO, respectively, are not included in rate base and are amortized over various periods.
	(c) $22.0 million not included in rate base and amortized over various periods.
	(d) $2.2 million not included in rate base and amortized over various periods.
	(e) Not included in rate base and amortized over various periods.
	(f) Not included in rate base and amortized through 2016.
	(g) Represents fair value of derivative instruments for commodity contracts. Settlements of the contracts are recognized in the income
	statement and included in fuel recovery mechanisms.
	(h) Included in rate base and amortized through 2038.
	(i) Included in rate base and amortized through 2058.
	(j) Not included in rate base and amortized through 2017.
	(k) Estimated cumulative net provision for future removal costs.

Goodwill_and_Intangible_Assets1

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Finite-Lived Intangible Assets [Table Text Block]	Great Plains Energy's and KCP&L's intangible assets are included in electric utility plant on the consolidated balance sheets and are detailed in the following table.
			December 31, 2014									December 31, 2013
		Gross Carrying Amount					Accumulated Amortization				Gross Carrying Amount					Accumulated Amortization
	Great Plains Energy	(millions)
	Computer software		$	300.2				$	(190.9	)		$	255.4				$	(169.9	)
	Asset improvements		27.4					(5.5		)		26.5					(4.9		)
	KCP&L
	Computer software		$	277.9				$	(175.5	)		$	231.2				$	(156.5	)
	Asset improvements		12.2					(1.3		)		11.2					(1.1		)
Amortization Expense Related to Intangible Assets [Table Text Block]	Great Plains Energy's and KCP&L's amortization expense related to intangible assets is detailed in the following table.
		2014			2013
		(millions)
	Great Plains Energy	$	21.6		$	17.6
	KCP&L	19.2			14.3
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	The following table provides the estimated amortization expense related to Great Plains Energy's and KCP&L's intangible assets for 2015 through 2019 for the intangible assets included in the consolidated balance sheets at December 31, 2014.
		2015			2016				2017		2018			2019
		(millions)
	Great Plains Energy	$	24.2		$	19			$	15	$	12.1		$	9.2
	KCP&L	21.8			16.1				13.9		11.7			8.8

Asset_Retirement_Obligations_T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]
Schedule of Change in Asset Retirement Obligation [Table Text Block]	The following table summarizes the change in Great Plains Energy's and KCP&L's AROs.
		Great Plains Energy				KCP&L
		2014		2013		2014		2013
		(millions)
	Beginning balance	$	158.8	$	149.3	$	141.7	$	133.2
	Revision in timing and/or estimates - Wolf Creek	23.9		—		23.9		—
	Revision in timing and/or estimates - other	2.9		—		2.9		—
	Accretion	10.3		9.5		9.2		8.5
	Ending balance	$	195.9	$	158.8	$	177.7	$	141.7

Pension_Plans_and_Other_Employ1

Pension Plans and Other Employee Benefits (Tables)	12 Months Ended
	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Schedule of Net Benefit Costs [Table Text Block]
			Pension Benefits												Other Benefits
			2014				2013				2012				2014				2013			2012
	Components of net periodic benefit costs		(millions)
	Service cost		$	36.7			$	41.2			$	35.4			$	3.7			$	4.4		$	3.3
	Interest cost		50.1				47.2				48.9				7.9				7.7			7.8
	Expected return on plan assets		(50.2		)		(47.1		)		(42.9		)		(2.6		)		(2.0		)	(1.8		)
	Prior service cost		0.9				2				4.5				3.1				7.2			7.1
	Recognized net actuarial (gain) loss		50				54.3				44.5				(0.1		)		1.7			(0.2		)
	Transition obligation		—				—				—				0.2				0.2			1.1
	Settlement charges		8.5				4.9				0.8				—				—			—
	Net periodic benefit costs before regulatory adjustment		96				102.5				91.2				12.2				19.2			17.3
	Regulatory adjustment		(11.3		)		(16.8		)		(15.5		)		4.3				(2.4		)	1.5
	Net periodic benefit costs		84.7				85.7				75.7				16.5				16.8			18.8
	Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
	Current year net (gain) loss		175.8				(147.0		)		97.9				(1.8		)		(22.1		)	27.1
	Amortization of gain (loss)		(50.0		)		(54.3		)		(44.5		)		0.1				(1.7		)	0.2
	Prior service cost		—				0.3				1.1				—				(6.0		)	—
	Amortization of prior service cost		(0.9		)		(2.0		)		(4.5		)		(3.1		)		(7.2		)	(7.1		)
	Amortization of transition obligation		—				—				—				(0.2		)		(0.2		)	(1.1		)
	Other regulatory activity		7.3				11.8				17.7				(4.2		)		2.1			(1.2		)
	Total recognized in OCI or regulatory asset/liability		132.2				(191.2		)		67.7				(9.2		)		(35.1		)	17.9
	Total recognized in net periodic benefit costs and OCI or regulatory asset/liability		$	216.9			$	(105.5	)		$	143.4			$	7.3			$	(18.3	)	$	36.7
Schedule of Net Funded Status [Table Text Block]
			Pension Benefits								Other Benefits
			2014				2013				2014				2013
	Change in projected benefit obligation (PBO)		(millions)
	PBO at January 1		$	1,007.40			$	1,130.50			$	160.5			$	186.5
	Service cost		36.7				41.2				3.7				4.4
	Interest cost		50.1				47.2				7.9				7.7
	Contribution by participants		—				—				6.8				6.2
	Amendments		—				0.3				—				(6.0		)
	Actuarial (gain) loss		181.1				(118.4		)		(0.3		)		(26.1		)
	Benefits paid		(49.0		)		(52.9		)		(13.4		)		(12.2		)
	Settlements		(39.5		)		(40.5		)		—				—
	PBO at December 31		$	1,186.80			$	1,007.40			$	165.2			$	160.5
	Change in plan assets
	Fair value of plan assets at January 1		$	703			$	666.4			$	101.2			$	90.3
	Actual return on plan assets		47.2				70.9				4.1				(2.0		)
	Contributions by employer and participants		66.2				57.4				18.6				25
	Benefits paid		(46.9		)		(51.2		)		(13.3		)		(12.1		)
	Settlements		(39.5		)		(40.5		)		—				—
	Fair value of plan assets at December 31		$	730			$	703			$	110.6			$	101.2
	Funded status at December 31		$	(456.8	)		$	(304.4	)		$	(54.6	)		$	(59.3	)
	Amounts recognized in the consolidated balance sheets
	Current pension and other post-retirement liability		$	(1.9	)		$	(2.3	)		$	(0.9	)		$	(0.9	)
	Noncurrent pension liability and other post-retirement liability		(454.9		)		(302.1		)		(53.7		)		(58.4		)
	Net amount recognized before regulatory treatment		(456.8		)		(304.4		)		(54.6		)		(59.3		)
	Accumulated OCI or regulatory asset/liability		500.5				368.3				26.1				35.3
	Net amount recognized at December 31		$	43.7			$	63.9			$	(28.5	)		$	(24.0	)
	Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
	Actuarial loss		$	273.5			$	147.7			$	17.5			$	19.2
	Prior service cost		4.7				5.6				13.5				16.6
	Transition obligation		—				—				0.2				0.4
	Other		222.3				215				(5.1		)		(0.9		)
	Net amount recognized at December 31		$	500.5			$	368.3			$	26.1			$	35.3
Schedule Of Periodic Benefit Obligation And Accumulated Benefit Obligation And Fair Value Of Plan Assets By Funded And Under Funded Plans [Table Text Block]
			2014				2013
	Pension plans with the PBO in excess of plan assets		(millions)
	Projected benefit obligation		$	1,186.80			$	1,007.40
	Fair value of plan assets		730				703
	Pension plans with the ABO in excess of plan assets
	Accumulated benefit obligation		$	1,036.80			$	889.2
	Fair value of plan assets		730				703
	Other post-retirement benefit plans with the APBO in excess of plan assets
	Accumulated other post-retirement benefit obligation		$	165.2			$	160.5
	Fair value of plan assets		110.6				101.2
Schedule of Assumptions Used [Table Text Block]
	Weighted-average assumptions used to determine the benefit obligation at December 31		Pension Benefits										Other Benefits
			2014					2013					2014					2013
	Discount rate		4.22	%				5.03	%				4.14	%				4.92	%
	Rate of compensation increase		3.62	%				3.69	%				3.5	%				3.5	%
	Weighted-average assumptions used to determine net costs for years ended December 31		Pension Benefits										Other Benefits
			2014					2013					2014					2013
	Discount rate		5.03	%				4.17	%				4.92	%				4.13	%
	Expected long-term return on plan assets		7.24	%				7.24	%				2.7	%	*			2.62	%	*
	Rate of compensation increase		3.69	%				3.69	%				3.5	%				3.5	%
	*after tax
Schedule of Expected Benefit Payments [Table Text Block]
			Pension Benefits				Other Benefits
			(millions)
	2015		$	76.5			$	7.5
	2016		74.9				8.1
	2017		76.7				8.6
	2018		78.2				9
	2019		80.2				9.4
	2020-2024		420.6				49.7
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]
	Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Description		Real Estate						Hedge Funds					Total
			(millions)
	Balance January 1, 2014			$	43.7					$	23.1					$	66.8
	Actual return on plan assets
	Relating to assets still held			3.1						1						4.1
	Relating to assets sold			1.2						—						1.2
	Purchase, sales and settlements, net			(23.1		)				—						(23.1		)
	Balance December 31, 2014			$	24.9					$	24.1					$	49
	Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Description		Real Estate						Hedge Funds						Total
			(millions)
	Balance January 1, 2013			$	38.4					$	21.6					$	60
	Actual return on plan assets
	Relating to assets still held			4.6						1.5						6.1
	Purchase, sales and settlements, net			0.7						—						0.7
	Balance December 31, 2013			$	43.7					$	23.1					$	66.8
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates [Table Text Block]
			Increase				Decrease
			(millions)
	Effect on total service and interest component		$	0.9			$	(1.1	)
	Effect on post-retirement benefit obligation		7.4				(6.1		)
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule of Allocation of Plan Assets [Table Text Block]
							Fair Value Measurements Using
		December 31					Quoted Prices in Active Markets for Identical Assets						Significant Other Observable Inputs						Significant Unobservable Inputs
		2014					(Level 1)						(Level 2)						(Level 3)
	Description
			(millions)
	Pension Plans
	Equity securities
	U.S. (a)		$	235.2				$	203.6					$	31.6					$	—
	International (b)		147.3					108.4						38.9						—
	Real estate (c)		38.9					7.7						6.3						24.9
	Commodities (d)		5.9					—						5.9						—
	Fixed income securities
	Fixed income funds (e)		66.1					22.3						43.8						—
	U.S. Treasury		44.2					44.2						—						—
	U.S. Agency, state and local obligations		21					—						21						—
	U.S. corporate bonds (f)		109					—						109						—
	Foreign corporate bonds		13.6					—						13.6						—
	Hedge funds (g)		24.1					—						—						24.1
	Cash equivalents		16.7					16.7						—						—
	Other		8					—						8						—
	Total		$	730				$	402.9					$	278.1					$	49
							Fair Value Measurements Using
		December 31					Quoted Prices in Active Markets for Identical Assets						Significant Other Observable Inputs						Significant Unobservable Inputs
		2013					(Level 1)						(Level 2)						(Level 3)
	Description
			(millions)
	Pension Plans
	Equity securities
	U.S. (a)		$	193.7				$	80.5					$	113.2					$	—
	International (b)		167.1					39.9						127.2						—
	Real estate (c)		49.1					—						5.4						43.7
	Commodities (d)		34.8					—						34.8						—
	Fixed income securities
	Fixed income funds (e)		181.3					27.1						154.2						—
	U.S. Treasury		2.6					2.6						—						—
	U.S. Agency, state and local obligations		17.1					—						17.1						—
	U.S. corporate bonds (f)		25.6					—						25.6						—
	Foreign corporate bonds		2.3					—						2.3						—
	Hedge funds (g)		23.1					—						—						23.1
	Cash equivalents		3					3						—						—
	Other		3.3					—						3.3						—
	Total		$	703				$	153.1					$	483.1					$	66.8
	(a) At December 31, 2014 and 2013, this category is comprised of $78.1 million and $80.5 million, respectively, of traded mutual funds valued at daily listed prices and $31.6 million and $113.2 million, respectively, of institutional common/collective trust funds valued at Net Asset Value (NAV) per share. At December 31, 2014, this category also included $125.5 million of traded common stocks and exchange traded funds.
	(b) At December 31, 2014 and 2013, this category is comprised of $38.6 million and $39.9 million, respectively, of traded mutual funds valued at daily listed prices and $38.6 million and $127.2 million, respectively, of institutional common/collective trust funds valued at daily NAV per share. At December 31, 2014, this category also included $70.1 million of traded American depository receipts, global depository receipts and ordinary shares.
	(c) At December 31, 2014 and 2013, this category is comprised of $7.7 million and none, respectively, of traded real estate investment trusts, $12.7 million and $32.6 million, respectively, of institutional common/collective trust funds and $18.5 million and $16.5 million, respectively, of a limited partnership valued at NAV on a quarterly basis.
	(d) This category is comprised of institutional common/collective trust funds valued at daily NAV per share.
	(e) At December 31, 2014 and 2013, this category is comprised of $22.3 million and $27.1 million, respectively, of traded mutual funds valued at daily listed prices and $43.8 million and $154.2 million, respectively, of institutional common/collective trust funds valued at daily NAV per share.
	(f) At December 31, 2014 and 2013, this category is comprised of $100.3 million and $20.1 million, respectively, of corporate bonds, $4.0 million and $3.6 million, respectively, of collateralized mortgage obligations and $4.7 million and $1.9 million, respectively, of other asset-backed securities.
	(g) This category is comprised of closely-held limited partnerships valued at NAV on a quarterly basis.
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule of Allocation of Plan Assets [Table Text Block]
							Fair Value Measurements Using
		December 31					Quoted Prices in Active Markets for Identical Assets						Significant Other Observable Inputs						Significant Unobservable Inputs
		2014					(Level 1)						(Level 2)						(Level 3)
	Description
			(millions)
	Other Post-Retirement Benefit Plans
	Equity securities		$	3.2				$	3.2					$	—					$	—
	Fixed income securities
	Fixed income fund (a)		73					0.2						72.8						—
	U.S. Treasury		2.7					2.7						—						—
	U.S. Agency, state and local obligations		4.9					—						4.9						—
	U.S. corporate bonds (b)		13					—						13						—
	Foreign corporate bonds		1.5					—						1.5						—
	Cash equivalents		10.4					10.4						—						—
	Other		1.9					—						1.9						—
	Total		$	110.6				$	16.5					$	94.1					$	—
							Fair Value Measurements Using
		December 31					Quoted Prices in Active Markets for Identical Assets						Significant Other Observable Inputs						Significant Unobservable Inputs
		2013					(Level 1)						(Level 2)						(Level 3)
	Description
			(millions)
	Other Post-Retirement Benefit Plans
	Equity securities		$	2.2				$	2.2					$	—					$	—
	Fixed income securities
	Fixed income fund (a)		74.6					0.2						74.4						—
	U.S. Treasury		1.5					1.5						—						—
	U.S. Agency, state and local obligations		4.4					—						4.4						—
	U.S. corporate bonds (b)		8.6					—						8.6						—
	Foreign corporate bonds		1					—						1						—
	Cash equivalents		8.6					8.6						—						—
	Other		0.3					—						0.3						—
	Total		$	101.2				$	12.5					$	88.7					$	—
	(a) At December 31, 2014 and 2013, this category is comprised of $72.8 million and $74.4 million, respectively, of an institutional common/collective trust fund valued at daily NAV per share and $0.2 million of traded mutual funds valued at daily listed prices.
	(b) At December 31, 2014 and 2013, this category is comprised of $10.3 million and $7.1 million, respectively, of corporate bonds, $0.8 million and $0.3 million, respectively, of collateralized mortgage obligations and $1.9 million and $1.2 million, respectively, of other asset-backed securities.

Equity_Compensation_Tables

Equity Compensation (Tables)	12 Months Ended
	Dec. 31, 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.
			2014		2013				2012
	Great Plains Energy		(millions)
	Equity compensation expense		$	9.9	$	5.6			$	3.3
	Income tax benefit		3.6		1.9				1.4
	KCP&L
	Equity compensation expense		$	6.9	$	4			$	2.3
	Income tax benefit		2.4		1.3				1
Performance share activity
		Performance			Grant Date
		Shares			Fair Value*
	Beginning balance January 1, 2014		430,009			$	23.52
	Granted		214,946			28.78
	Earned		(107,741	)		26.14
	Forfeited		(2,927	)		25.73
	Performance adjustment		(271	)
	Ending balance December 31, 2014		534,016			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		81,290			25.7
	Vested		(101,174	)		18.96
	Forfeited		(1,263	)		24.16
	Ending balance December 31, 2014		267,390			22.31
	* weighted-average
Director Deferred Share Units
			Share Units			Grant Date Fair Value*
	Beginning balance January 1, 2014			90,120			$	20.94
	Issued			20,621			26.53
	Ending balance December 31, 2014			110,741			21.98
	* weighted-average

LongTerm_Debt_Tables

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 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.
				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
	0.05% 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				(3.8		)			(4.1		)
	Total KCP&L excluding current maturities				2,298.50					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				4.3					4.9
	Total Great Plains Energy excluding current maturities				$	3,488.00				$	3,515.70
	(a)	Weighted-average interest rates at December 31, 2014
	(b)	Rate after amortizing gains/losses recognized in OCI on settlements of interest rate hedging instruments
	(c)	Variable rate
Amortization Of Debt Expense [Table Text Block]	Great Plains Energy's and KCP&L's amortization of debt expense is detailed in the following table.
			2014				2013			2012
			(millions)
	KCP&L		$	3			$	3.2		$	2.9
	Other Great Plains Energy		1.8				2.5			2.6
	Total Great Plains Energy		$	4.8			$	5.7		$	5.5
Schedule of Maturities of Long-term Debt [Table Text Block]	Great Plains Energy's and KCP&L's long-term debt maturities for the next five years are detailed in the following table.
			2015				2016			2017			2018		2019
			(millions)
	Great Plains Energy		$	15.1			$	1.1		$	382.1		$	351.1	$	401.1
	KCP&L		14				—			281			350		400

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Schedule of Rent Expense [Table Text Block]
		2014		2013			2012
		(millions)
	Great Plains Energy	$	16	$	18.5		$	21.8
	KCP&L	14		16			17.7
Unrecorded Unconditional Purchase Obligations And Lease Commitments [Table Text Block]	Great Plains Energy's and KCP&L's contractual commitments at December 31, 2014, excluding pensions and long-term debt, are detailed in the following tables.
	Great Plains Energy
		2015			2016				2017		2018		2019		After 2019			Total
	Lease commitments	(millions)
	Operating lease	$	14.2		$	10			$	9.7	$	9.7	$	9		$	129.5		$	182.1
	Capital lease	0.4			0.4				0.4		0.4		0.4			4			6
	Purchase commitments
	Fuel	374.6			184.9				163		112.2		138.2			70.9			1,043.80
	Power	47.3			47.3				47.3		47.3		47.3			556.8			793.3
	Capacity	3			1.2				—		—		—			—			4.2
	La Cygne environmental project	16.6			—				—		—		—			—			16.6
	Non-regulated natural gas transportation	3.5			3.5				1		—		—			—			8
	Other	44.8			31.1				10		12.8		12			44.2			154.9
	Total contractual commitments	$	504.4		$	278.4			$	231.4	$	182.4	$	206.9		$	805.4		$	2,208.90
	KCP&L
		2015			2016				2017		2018		2019		After 2019			Total
	Lease commitments	(millions)
	Operating lease	$	12.8		$	9.9			$	9.7	$	9.7	$	9		$	129.5		$	180.6
	Capital lease	0.2			0.2				0.2		0.2		0.2			2			3
	Purchase commitments
	Fuel	318.8			138.2				130.8		81.5		114.4			70.9			854.6
	Power	34.8			34.8				34.8		34.8		34.8			394.6			568.6
	Capacity	3			1.2				—		—		—			—			4.2
	La Cygne environmental project	16.6			—				—		—		—			—			16.6
	Other	41.1			29.7				8.6		11.4		10.6			36.2			137.6
	Total contractual commitments	$	427.3		$	214			$	184.1	$	137.6	$	169		$	633.2		$	1,765.20

Related_Party_Transactions_and1

Related Party Transactions and Relationships (Tables)	12 Months Ended
	Dec. 31, 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.
		December 31
		2014		2013
		(millions)
	Net receivable from GMO	$	38.2	$	32.7
	Net receivable from Great Plains Energy	18		17.5

Derivative_Instruments_Tables

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 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.
		December 31
		2014								2013
		Notional				Fair				Notional				Fair
		Contract				Value				Contract				Value
		Amount								Amount
	Great Plains Energy	(millions)
	Futures contracts
	Non-hedging derivatives	$	14.9			$	(2.4	)		$	19.3			$	(0.6	)
	Forward contracts
	Non-hedging derivatives	29.7				4.1				47.7				5.2
	Transmission congestion rights
	Non-hedging derivatives	28.3				2.6				22.9				1.7
	Option contracts
	Non-hedging derivatives	1.7				0.1				4.8				1.2
	KCP&L
	Futures contracts
	Non-hedging derivatives	$	—			$	—			$	7.7			$	(0.2	)
	Transmission congestion rights
	Non-hedging derivatives	23.6				3.1				18				1.1
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
	December 31, 2014	Classification		Fair Value						Fair Value
	Derivatives Not Designated as Hedging Instruments				(millions)
	Commodity contracts	Other			$	8.6					$	4.2
	December 31, 2013
	Derivatives Not Designated as Hedging Instruments
	Commodity contracts	Other			$	8.5					$	1
	KCP&L
		Balance Sheet		Asset Derivatives						Liability Derivatives
	December 31, 2014	Classification		Fair Value						Fair Value
	Derivatives Not Designated as Hedging Instruments				(millions)
	Commodity contracts	Other			$	4					$	0.9
	December 31, 2013
	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			Net Amount
	31-Dec-14	(millions)
	Derivative assets		$	8.6					$	(1.2	)				$	7.4		$	—		$	—		$	7.4
	Derivative liabilities		4.2						(3.5		)				0.7			—			—			0.7
	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			Net Amount
	31-Dec-14	(millions)
	Derivative assets		$	4					$	(0.9	)				$	3.1		$	—		$	—		$	3.1
	Derivative liabilities		0.9						(0.9		)				—			—			—			—
	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
	Derivatives Not Designated as Hedging Instruments		2014				2013				2012
	Location of Gain (Loss)		(millions)
	Electric revenues		$	(14.2	)		$	—			$	—
	Fuel		1.5				(1.1		)		(6.6		)
	Purchased power		(4.9		)		—				—
	Regulatory asset		(2.7		)		—				(3.7		)
	Regulatory liability		—				0.2				—
	Total		$	(20.3	)		$	(0.9	)		$	(10.3	)
	KCP&L
	Derivatives Not Designated as Hedging Instruments		2014				2013				2012
	Location of Gain (Loss)		(millions)
	Electric revenues		$	(14.2	)		$	—			$	—
	Fuel		1.1				0.8				—
	Regulatory asset		(0.2		)		—				—
	Total		$	(13.3	)		$	0.8			$	—

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 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.
	Description	December 31							Level 1		Level 2				Level 3
		2014
	KCP&L		(millions)
	Assets
	Nuclear decommissioning trust (a)
	Equity securities		$	137.1					$	137.1		$	—			$	—
	Debt securities
	U.S. Treasury		22.9						22.9			—				—
	U.S. Agency		3.5						—			3.5				—
	State and local obligations		4.1						—			4.1				—
	Corporate bonds		28.1						—			28.1				—
	Foreign governments		0.5						—			0.5				—
	Cash equivalents		2.3						2.3			—				—
	Other		0.5						—			0.5				—
	Total nuclear decommissioning trust		199						162.3			36.7				—
	Self-insured health plan trust (b)
	Equity securities		1.3						1.3			—				—
	Debt securities		7.6						—			7.6				—
	Cash and cash equivalents		6.2						6.2			—				—
	Total self-insured health plan trust		15.1						7.5			7.6				—
	Derivative instruments (c)		4						—			—				4
	Total		$	218.1					$	169.8		$	44.3			$	4
	Liabilities
	Derivative instruments (c)		0.9						—			—				0.9
	Total		$	0.9					$	—		$	—			$	0.9
	Other Great Plains Energy
	Assets
	Derivative instruments (c)		$	4.6					$	—		$	3.4			$	1.2
	SERP rabbi trusts (d)
	Equity securities		0.1						0.1			—				—
	Fixed income funds		17.8						—			17.8				—
	Total SERP rabbi trusts		17.9						0.1			17.8				—
	Total		22.5						0.1			21.2				1.2
	Liabilities
	Derivative instruments (c)		3.3						2.4			0.1				0.8
	Total		$	3.3					$	2.4		$	0.1			$	0.8
	Great Plains Energy
	Assets
	Nuclear decommissioning trust (a)		$	199					$	162.3		$	36.7			$	—
	Self-insured health plan trust (b)		15.1						7.5			7.6				—
	Derivative instruments (c)		8.6						—			3.4				5.2
	SERP rabbi trusts (d)		17.9						0.1			17.8				—
	Total		240.6						169.9			65.5				5.2
	Liabilities
	Derivative instruments (c)		4.2						2.4			0.1				1.7
	Total		$	4.2					$	2.4		$	0.1			$	1.7
	Description	December 31						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)		1.2						0.1			—				1.1
Total		$	199.9					$	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)		$	7.3					$	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		26						0.3			23.5				2.2
Liabilities
Derivative instruments (c)		0.7						0.6			0.1				—
Total		$	0.7					$	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)		8.5						0.3			4.9				3.3
SERP rabbi trusts (d)		18.7						0.1			18.6				—
Total		225.9						157.9			64.7				3.3
Liabilities
Derivative instruments (c)		1						0.9			0.1				—
Total		$	1					$	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 for equity securities and NAV per share for fixed income funds. The fixed income fund invests primarily in intermediate and long-term debt securities, can be redeemed immediately and is not subject to any restrictions on redemptions.
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 January 1	$	3.3			$	2.3
	Total realized/unrealized gains (losses):
	included in electric revenue	(14.2		)		—
	included in purchased power expense	(4.9		)		—
	included in non-operating income	14.6				9.5
	included in regulatory asset	(0.1		)		—
	Purchases	16				1.7
	Settlements	(11.2		)		(10.2		)
	Net asset at December 31	$	3.5			$	3.3
	Total unrealized losses relating to assets still on the consolidated balance sheet at December 31:
	included in electric revenue	$	(0.2	)		$	—
	included in non-operating income	(0.3		)		(0.3		)
	included in regulatory asset	(0.1		)		—
	KCP&L
	Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
		Derivative Instruments
		2014				2013
		(millions)
	Net asset at January 1	$	1.1			$	—
	Total realized/unrealized gains (losses):
	included in electric revenue	(14.2		)		—
	included in regulatory asset	(0.2		)		—
	Purchases	13.7				1.1
	Settlements	2.7				—
	Net asset at December 31	$	3.1			$	1.1
	Total unrealized losses relating to assets still on the consolidated balance sheet at December 31:
	included in electric revenue	$	(0.2	)		$	—
	included in regulatory asset	(0.2		)		—

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 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)
		(millions)
	2014
	Beginning balance January 1		$	(23.8	)				$	(1.5	)	$	(25.3	)
	Other comprehensive loss before reclassifications		—						(1.8		)	(1.8		)
	Amounts reclassified from accumulated other comprehensive loss		8						0.4			8.4
	Net current period other comprehensive income (loss)		8						(1.4		)	6.6
	Ending balance December 31		$	(15.8	)				$	(2.9	)	$	(18.7	)
	2013
	Beginning balance January 1		$	(35.4	)				$	(3.0	)	$	(38.4	)
	Other comprehensive income before reclassifications		—						1.2			1.2
	Amounts reclassified from accumulated other comprehensive loss		11.6						0.3			11.9
	Net current period other comprehensive income		11.6						1.5			13.1
	Ending balance December 31		$	(23.8	)				$	(1.5	)	$	(25.3	)
	(a) Net of tax
	KCP&L
		Gains and Losses on Cash Flow Hedges(a)
		(millions)
	2014
	Beginning balance January 1		$	(20.2	)
	Amounts reclassified from accumulated other comprehensive loss		5.3
	Net current period other comprehensive income		5.3
	Ending balance December 31		$	(14.9	)
	2013
	Beginning balance January 1		$	(25.8	)
	Amounts reclassified from accumulated other comprehensive loss		5.6
	Net current period other comprehensive income		5.6
	Ending balance December 31		$	(20.2	)
	(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
		2014				2013
		(millions)
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts	$	(13.1	)		$	(18.6	)		Interest charges
	Commodity contracts	—				(0.3		)		Fuel
		(13.1		)		(18.9		)		Income before income tax expense and loss from equity investments
		5.1				7.3				Income tax benefit
		$	(8.0	)		$	(11.6	)		Net income
	Amortization of defined benefit pension items
	Net losses included in net periodic benefit costs	$	(0.6	)		$	(0.5	)		Utility operating and maintenance expenses
		(0.6		)		(0.5		)		Income before income tax expense and loss from equity investments
		0.2				0.2				Income tax benefit
		$	(0.4	)		$	(0.3	)		Net income
	Total reclassifications, net of tax	$	(8.4	)		$	(11.9	)		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
		2014				2013
		(millions)
	Gains and (losses) on cash flow hedges (effective portion)
	Interest rate contracts	$	(8.7	)		$	(8.8	)		Interest charges
	Commodity contracts	—				(0.3		)		Fuel
		(8.7		)		(9.1		)		Income before income tax expense
		3.4				3.5				Income tax benefit
	Total reclassifications, net of tax	$	(5.3	)		$	(5.6	)		Net income

Taxes_Tables

Taxes (Tables)	12 Months Ended
	Dec. 31, 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.
	Great Plains Energy	2014				2013				2012
	Current income taxes	(millions)
	Federal	$	0.4			$	0.3			$	(3.2	)
	State	(0.1		)		(3.0		)		(6.3		)
	Total	0.3				(2.7		)		(9.5		)
	Deferred income taxes
	Federal	104.2				109.1				96.3
	State	21.6				24.9				24.9
	Total	125.8				134				121.2
	Noncurrent income taxes
	Federal	(2.4		)		—				(0.2		)
	State	(0.5		)		(0.3		)		(0.3		)
	Foreign	(6.1		)		(0.4		)		(4.2		)
	Total	(9.0		)		(0.7		)		(4.7		)
	Investment tax credit
	Deferral	—				0.3				—
	Amortization	(1.4		)		(1.7		)		(2.4		)
	Total	(1.4		)		(1.4		)		(2.4		)
	Income tax expense	$	115.7			$	129.2			$	104.6
	KCP&L	2014				2013				2012
	Current income taxes	(millions)
	Federal	$	(9.4	)		$	(0.5	)		$	13.1
	State	(2.3		)		(0.5		)		2
	Total	(11.7		)		(1.0		)		15.1
	Deferred income taxes
	Federal	72.6				75.8				48.8
	State	15.8				16.3				11.4
	Total	88.4				92.1				60.2
	Noncurrent income taxes
	Federal	—				(9.0		)		1.7
	State	—				(1.5		)		0.1
	Total	—				(10.5		)		1.8
	Investment tax credit
	Deferral	—				0.3				—
	Amortization	(1.0		)		(1.1		)		(1.8		)
	Total	(1.0		)		(0.8		)		(1.8		)
	Income tax expense	$	75.7			$	79.8			$	75.3
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]
	Great Plains Energy	2014			2013			2012
	Federal statutory income tax rate	35	%		35	%		35	%
	Differences between book and tax depreciation not normalized	(0.7	)		(0.3	)		1.2
	Amortization of investment tax credits	(0.4	)		(0.4	)		(0.8	)
	Federal income tax credits	(3.8	)		(3.5	)		(3.1	)
	State income taxes	3.8			3.8			4
	Changes in uncertain tax positions, net	(1.7	)		(0.2	)		(1.5	)
	Other	0.1			(0.4	)		(0.5	)
	Effective income tax rate	32.3	%		34	%		34.3	%
	KCP&L	2014			2013			2012
	Federal statutory income tax rate	35	%		35	%		35	%
	Differences between book and tax depreciation not normalized	(0.9	)		(0.8	)		1.3
	Amortization of investment tax credits	(0.4	)		(0.4	)		(0.8	)
	Federal income tax credits	(5.6	)		(5.3	)		(4.3	)
	State income taxes	3.7			3.7			4.1
	Other	—			(0.1	)		(0.6	)
	Effective income tax rate	31.8	%		32.1	%		34.7	%
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]
			Great Plains Energy								KCP&L
	December 31		2014				2013				2014				2013
	Current deferred income tax asset (liability)		(millions)
	Net operating loss carryforward		$	62.2			$	76.6			$	—			$	—
	Other		17.1				5.7				5				(1.7		)
	Net current deferred income tax asset (liability) before valuation allowance		79.3				82.3				5				(1.7		)
	Valuation allowance		(1.2		)		(2.0		)		—				—
	Net current deferred income tax asset (liability)		78.1				80.3				5				(1.7		)
	Noncurrent deferred income taxes
	Plant related		(1,648.2		)		(1,433.8		)		(1,167.3		)		(1,022.9		)
	Income taxes on future regulatory recoveries		(133.4		)		(136.4		)		(107.1		)		(111.0		)
	Derivative instruments		26.5				32.3				18.9				23.4
	Pension and post-retirement benefits		(14.0		)		(28.2		)		12.5				(1.7		)
	SO2 emission allowance sales		27.1				28.8				27.3				28.8
	Tax credit carryforwards		242.7				229.3				153.2				139.6
	Customer demand programs		(26.2		)		(27.7		)		(19.0		)		(19.4		)
	Solar rebates		(33.2		)		(17.5		)		(11.3		)		(5.1		)
	Net operating loss carryforward		524.7				446.7				98.5				71.6
	Other		(40.3		)		(39.6		)		(22.6		)		(25.4		)
	Net noncurrent deferred income tax liability before valuation allowance		(1,074.3		)		(946.1		)		(1,016.9		)		(922.1		)
	Valuation allowance		(15.4		)		(18.7		)		—				—
	Net noncurrent deferred income tax liability		(1,089.7		)		(964.8		)		(1,016.9		)		(922.1		)
	Net deferred income tax liability		$	(1,011.6	)		$	(884.5	)		$	(1,011.9	)		$	(923.8	)
			Great Plains Energy								KCP&L
	December 31		2014				2013				2014				2013
			(millions)
	Gross deferred income tax assets		$	1,227.00			$	1,148.20			$	624.8			$	583
	Gross deferred income tax liabilities		(2,238.6		)		(2,032.7		)		(1,636.7		)		(1,506.8		)
	Net deferred income tax liability		$	(1,011.6	)		$	(884.5	)		$	(1,011.9	)		$	(923.8	)
Summary of Income Tax Contingencies [Table Text Block]	The following table reflects activity for Great Plains Energy and KCP&L related to the liability for unrecognized tax benefits.
		Great Plains Energy												KCP&L
		2014				2013				2012				2014				2013			2012
		(millions)
	Beginning balance January 1	$	9.8			$	21.4			$	24			$	—			$	10.5		$	8.7
	Additions for current year tax positions	—				—				3.7				—				—			3.6
	Reductions for current year tax positions	(0.3		)		(0.3		)		—				—				—			—
	Reductions for prior year tax positions	(6.9		)		(10.5		)		(1.8		)		—				(10.5		)	(1.6		)
	Statute expirations	—				(0.3		)		(4.7		)		—				—			(0.2		)
	Foreign currency translation adjustments	—				(0.5		)		0.2				—				—			—
	Ending balance December 31	$	2.6			$	9.8			$	21.4			$	—			$	—		$	10.5

Segments_and_Related_Informati1

Segments and Related Information (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Segment Financial Information [Table Text Block]
	2014	Electric				Other				Eliminations				Great Plains
		Utility												Energy
			(millions)
	Operating revenues		$	2,568.20			$	—			$	—			$	2,568.20
	Depreciation and amortization		(306.0		)		—				—				(306.0		)
	Interest (charges) income		(183.0		)		(41.2		)		35.7				(188.5		)
	Income tax (expense) benefit		(125.6		)		9.9				—				(115.7		)
	Net income (loss)		243.5				(0.7		)		—				242.8
	2013	Electric				Other				Eliminations				Great Plains
		Utility												Energy
			(millions)
	Operating revenues		$	2,446.30			$	—			$	—			$	2,446.30
	Depreciation and amortization		(289.7		)		—				—				(289.7		)
	Interest (charges) income		(190.5		)		(55.5		)		47.6				(198.4		)
	Income tax (expense) benefit		(135.4		)		6.2				—				(129.2		)
	Net income (loss)		257.1				(6.9		)		—				250.2
	2012	Electric				Other				Eliminations				Great Plains
		Utility												Energy
			(millions)
	Operating revenues		$	2,309.90			$	—			$	—			$	2,309.90
	Depreciation and amortization		(272.3		)		—				—				(272.3		)
	Interest (charges) income		(197.3		)		(67.3		)		43.8				(220.8		)
	Income tax (expense) benefit		(122.0		)		17.4				—				(104.6		)
	Net income (loss)		216.6				(16.7		)		—				199.9
		Electric				Other				Eliminations				Great Plains
		Utility												Energy
	2014		(millions)
	Assets		$	10,746.10			$	33.1			$	(303.5	)		$	10,475.70
	Capital expenditures		773.7				—				—				773.7
	2013
	Assets		$	10,019.60			$	105.6			$	(329.8	)		$	9,795.40
	Capital expenditures		669				—				—				669
	2012
	Assets		$	9,910.60			$	122.4			$	(385.7	)		$	9,647.30
	Capital expenditures		610.2				—				—				610.2

Jointly_Owned_Electric_Utility1

Jointly Owned Electric Utility Plants (Tables)	12 Months Ended
	Dec. 31, 2014
Jointly Owned Electric Utility Plants [Abstract]
Schedule of Jointly Owned Utility Plants [Table Text Block]	Great Plains Energy's and KCP&L's share of jointly-owned electric utility plants at December 31, 2014, are detailed in the following tables.
	Great Plains Energy
		Wolf Creek Unit			La Cygne Units			Iatan No. 1 Unit			Iatan No. 2 Unit			Iatan Common			Jeffrey Energy Center
		(millions, except MW amounts)
	Great Plains Energy's share		47%			50%			88%			73%			79%			8%
	Utility plant in service		$	1,745.60		$	562.6		$	645.8		$	1,318.30		$	441.2		$	172.7
	Accumulated depreciation		832.4			320.4			261.8			342			99			77.3
	Nuclear fuel, net		79.2			—			—			—			—			—
	Construction work in progress		74.6			533.9			19.3			16.6			18.6			19.9
	2015 accredited capacity-MWs		549			696			627			641			NA			172
	KCP&L
		Wolf Creek Unit			La Cygne Units			Iatan No. 1 Unit			Iatan No. 2 Unit			Iatan Common
		(millions, except MW amounts)
	KCP&L's share		47%			50%			70%			55%			61%
	Utility plant in service		$	1,745.60		$	562.6		$	515.4		$	1,006.80		$	357.8
	Accumulated depreciation		832.4			320.4			211.4			313.9			89.2
	Nuclear fuel, net		79.2			—			—			—			—
	Construction work in progress		74.6			533.9			5.4			7.8			2.4
	2015 accredited capacity-MWs		549			696			499			482			NA

Quarterly_Operating_Results_Un1

Quarterly Operating Results (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information [Table Text Block]
		Quarter
	Great Plains Energy	1st		2nd		3rd		4th
	2014	(millions, except per share amounts)
	Operating revenue	$	585.1	$	648.4	$	782.5	$	552.2
	Operating income	77.9		124.2		263.2		69.2
	Net income	23.8		52.1		147.4		19.5
	Basic earnings per common share	0.15		0.34		0.96		0.12
	Diluted earnings per common share	0.15		0.34		0.95		0.12
	2013
	Operating revenue	$	542.2	$	600.3	$	765	$	538.8
	Operating income	86.1		143.6		271.7		67.8
	Net income	26		63.6		143.1		17.5
	Basic and diluted earnings per common share	0.17		0.41		0.93		0.11
		Quarter
	KCP&L	1st		2nd		3rd		4th
	2014	(millions)
	Operating revenue	$	391	$	439.5	$	533.4	$	366.9
	Operating income	47.5		78.2		177.2		47.2
	Net income	17.2		34.8		94.5		15.9
	2013
	Operating revenue	$	366.7	$	410.8	$	522	$	371.9
	Operating income	52.3		93.4		176.8		40
	Net income	16.2		44.2		96.4		12.2

Summary_of_Significant_Account3

Summary of Significant Accounting Policies Equity Method Investment (Details) (Transource Energy, LLC [Member])	12 Months Ended
	Dec. 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%

Summary_of_Significant_Account4

Summary of Significant Accounting Policies Summary of Significant Accounting Policies Utility Plant (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	3.00%
Depreciation	$277.90		$265.40		$251.40
Depreciation and amortization	306		289.7		272.3
Utility Plant, at original cost
Public Utilities, Property, Plant and Equipment, Generation or Processing	7,169.60		6,874.60
Public Utilities, Property, Plant and Equipment, Transmission	821.9		794
Public Utilities, Property, Plant and Equipment, Distribution	3,311.60		3,149.40
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment	825.6		757.3
Public Utilities, Property, Plant and Equipment, Plant in Service	12,128.70	[1]	11,575.30	[1]
Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life	20 years
Public Utilities, Property, Plant and Equipment, Transmission, Useful Life	15 years
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	8 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	5 years
Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life	60 years
Public Utilities, Property, Plant and Equipment, Transmission, Useful Life	70 years
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	66 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	50 years
Land and other assets not depreciated [Member]
Utility Plant, at original cost
Public Utilities, Property, Plant and Equipment, Plant in Service	127.9		107.8
Kansas City Power and Light Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation	189.7		179.2		168
Depreciation and amortization	213.9		198.3		185.6
Public Utilities, Allowance for Funds Used During Construction, Rate	5.70%		6.10%		2.00%
Utility Plant, at original cost
Public Utilities, Property, Plant and Equipment, Generation or Processing	5,554.30		5,288.30
Public Utilities, Property, Plant and Equipment, Transmission	448.9		433.7
Public Utilities, Property, Plant and Equipment, Distribution	2,089		1,970.20
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment	645.1		582.7
Public Utilities, Property, Plant and Equipment, Plant in Service	8,737.30	[2]	8,274.90	[2]
Kansas City Power and Light Company [Member] | Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life	20 years
Public Utilities, Property, Plant and Equipment, Transmission, Useful Life	15 years
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	8 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	5 years
Kansas City Power and Light Company [Member] | Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life	60 years
Public Utilities, Property, Plant and Equipment, Transmission, Useful Life	70 years
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	55 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	50 years
Kansas City Power and Light Company [Member] | Land and other assets not depreciated [Member]
Utility Plant, at original cost
Public Utilities, Property, Plant and Equipment, Plant in Service	$72.40		$54.10
KCPL Greater Missouri Operations [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Allowance for Funds Used During Construction, Rate	6.10%		2.10%		2.40%
[1]	Includes $127.9 million and $107.8 million at December 31, 2014 and 2013, respectively, of land and other assets that are not depreciated.
[2]	Includes $72.4 million and $54.1 million at December 31, 2014 and 2013, respectively, of land and other assets that are not depreciated.

Summary_of_Significant_Account5

Summary of Significant Accounting Policies Summary of Significant Accounting Policies Revenue Recognition (Details) (Kansas City Power and Light Company [Member], USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Kansas City Power and Light Company [Member]
Excise and Sales Taxes	$60.40	$58.90	$55.80

Summary_of_Significant_Account6

Summary of Significant Accounting Policies Earnings Per Share (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Net income (loss)									$242.80	$250.20	$199.90
Income [Abstract]
Less: preferred stock dividend requirements									1.6	1.6	1.6
Earnings (loss) available for common shareholders									$241.20	$248.60	$198.30
Common Shares Outstanding [Abstract]
Average number of common shares outstanding (in shares)									153.9	153.5	145.5
Add: effect of dilutive securities (in shares)									0.2	0.2	1.7
Diluted average number of common shares outstanding (in shares)									154.1	153.7	147.2
Earnings Per Share [Abstract]
Earnings Per Share, Basic	$0.12	$0.96	$0.34	$0.15					$1.57	$1.62	$1.36
Earnings Per Share, Diluted	$0.12	$0.95	$0.34	$0.15					$1.57	$1.62	$1.35
Earnings Per Share, Basic and Diluted					$0.11	$0.93	$0.41	$0.17

Summary_of_Significant_Account7

Summary of Significant Accounting Policies Antidilutive Securities (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Performance Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	482,987	548,242	0
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	3,287	2,228	3,781

Summary_of_Significant_Account8

Summary of Significant Accounting Policies Subsequent Events (Details) (Dividend Declared [Member], USD $)	1 Months Ended
	Feb. 28, 2015	Feb. 10, 2015
Common Stock [Member]
Dividends Declared [Abstract]
Dividends Payable, Amount Per Share		$0.25
Subsequent Event, Description	Great Plains Energy's Board of Directors (Board) declared a quarterly dividend
Preferred Stock [Member]
Dividends Declared [Abstract]
Subsequent Event, Description	The Board also declared regular dividends on Great Plains Energy's preferred stock

Supplemental_Cash_Flow_Informa2

Supplemental Cash Flow Information (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows affected by changes in:
Receivables	$3	($7.10)	$76.80
Accounts receivable pledged as collateral	4	-1	-79
Fuel inventories	-13.7	18.7	-6.1
Materials and supplies	-0.4	-1	-11
Accounts payable	15.2	26.4	57.3
Accrued taxes	8.3	2.2	-7.8
Accrued interest	-4.1	3.9	-35.2
Deferred refueling outage costs	17	-17.6	15.6
Pension and post-retirement benefit obligations	25.5	31.3	14.4
Allowance for equity funds used during construction	-18	-14.1	-1.3
Fuel recovery mechanism	-28.5	-1.3	22.5
Solar rebates paid	-43.2	-32.5	-15.9
Uncertain tax positions	-9	-0.8	-4.7
Other operating activities	-3.3	17	-13.9
Total other operating activities	-47.2	24.1	11.7
Cash paid during the period:
Interest Paid, Net	174.8	170.8	247.9
Income Taxes Paid	0	0	3.3
Non-cash investing activities:
Liabilities accrued for capital expenditures	57.4	48.1	57.5
Kansas City Power and Light Company [Member]
Cash flows affected by changes in:
Receivables	-18.1	-12.6	8.8
Accounts receivable pledged as collateral	0	0	-15
Fuel inventories	-8.5	13.3	-4.6
Materials and supplies	-1.1	1.1	-9
Accounts payable	20.4	7.3	48.3
Accrued taxes	-42.5	-3.7	-2
Accrued interest	-0.1	1.4	-2.3
Deferred refueling outage costs	17	-17.6	15.6
Pension and post-retirement benefit obligations	26.9	35.7	18
Allowance for equity funds used during construction	-16	-14.1	-1.3
Fuel recovery mechanism	-2.2	-1.8	5.1
Solar rebates paid	-17.3	-8.2	-5.8
Uncertain tax positions	0	-10.5	1.8
Other operating activities	-23.2	0.5	-29.7
Total other operating activities	-64.7	-9.2	27.9
Cash paid during the period:
Interest Paid, Net	112.1	111.7	118
Income Taxes Paid	30.2	4.6	18
Non-cash investing activities:
Liabilities accrued for capital expenditures	$48.80	$40.50	$48.40

Receivables_Details

Receivables (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Accounts Receivable Sold [Line Items]
Receivables (sold) purchased	$0		$0
Gain (Loss) on Sale of Accounts Receivable	0.1	[1]	-0.2	[1]
Servicing fees received (paid)	0		0
Fees paid to outside investor	-1.7		-1.9
Cash from customers (transferred) received	0		0
Cash received from (paid for) receivables purchased	0		0
Interest on intercompany note received (paid)	0		0
Kansas City Power and Light Company [Member]
Accounts Receivable Sold [Line Items]
Receivables (sold) purchased	0		0
Gain (Loss) on Sale of Accounts Receivable	0	[1]	-0.1	[1]
Servicing fees received (paid)	0		0
Fees paid to outside investor	-1.1		-1.2
Cash from customers (transferred) received	0		0
Cash received from (paid for) receivables purchased	0		0
Interest on intercompany note received (paid)	0		0
Kansas City Power And Light Company Unconsolidated [Member]
Accounts Receivable Sold [Line Items]
Receivables (sold) purchased	-1,595.80		-1,517.20
Gain (Loss) on Sale of Accounts Receivable	-20.2	[1]	-19.2	[1]
Servicing fees received (paid)	2.6		2.6
Fees paid to outside investor	0		0
Cash from customers (transferred) received	-1,608.30		-1,516.20
Cash received from (paid for) receivables purchased	1,588.10		1,497.20
Interest on intercompany note received (paid)	0.3		0.3
KCPL Receivables Company [Member]
Accounts Receivable Sold [Line Items]
Receivables (sold) purchased	1,595.80		1,517.20
Gain (Loss) on Sale of Accounts Receivable	20.2	[1]	19.1	[1]
Servicing fees received (paid)	-2.6		-2.6
Fees paid to outside investor	-1.1		-1.2
Cash from customers (transferred) received	1,608.30		1,516.20
Cash received from (paid for) receivables purchased	-1,588.10		-1,497.20
Interest on intercompany note received (paid)	-0.3		-0.3
KCPL Greater Missouri Operations [Member]
Accounts Receivable Sold [Line Items]
Receivables (sold) purchased	-816.3		-834.7
Gain (Loss) on Sale of Accounts Receivable	-10.3	[1]	-10.6	[1]
Servicing fees received (paid)	1.2		1.4
Fees paid to outside investor	0		0
Cash from customers (transferred) received	-823.5		-830.9
Cash received from (paid for) receivables purchased	813.1		820.5
Interest on intercompany note received (paid)	0.1		0.1
GMO Receivables Company Member
Accounts Receivable Sold [Line Items]
Receivables (sold) purchased	816.3		834.7
Gain (Loss) on Sale of Accounts Receivable	10.4	[1]	10.5	[1]
Servicing fees received (paid)	-1.2		-1.4
Fees paid to outside investor	-0.6		-0.7
Cash from customers (transferred) received	823.5		830.9
Cash received from (paid for) receivables purchased	-813.1		-820.5
Interest on intercompany note received (paid)	($0.10)		($0.10)
[1]	Any net gain (loss) is the result of the timing difference inherent in collecting receivables and over the life of the agreement will net to zero.

Receivables_Accounts_Notes_and

Receivables Accounts, Notes, and Financing (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other Receivables, Gross, Current	$86.70	$88.60
Receivables, net	160.3	162.2
Kansas City Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other Receivables, Gross, Current	79.8	77.8
Receivables, net	128.9	129.2
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	-2.8	-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	-1.2	-1.1
Trade Accounts Receivable [Member] | Billed Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	1.1	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	0.6	1.3
Trade Accounts Receivable [Member] | Unbilled Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	75.3	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	$49.70	$51.20

Receivables_Narrative_Details

Receivables Narrative (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 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 mid-June 2015 through September 2015	80
Maximum amount of outstanding principal under receivables agreement from mid-November 2014 to mid-June 2015	$65

Nuclear_Plant_Details

Nuclear Plant (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investments in decommissioning trust fund [Line Items]
Cost Basis	$145.40	$138.10
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	54.4	47.1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	-0.8	-1.3
Fair Value, Nuclear decommissioning trust fund	199	183.9	154.7
Weighted average maturity of debt securities (in years)	7 years 0 months
Realized gains on investments in decommissioning trust fund	1.4	2.4	1.7
Realized losses on investments in decommissioning trust fund	-1	-0.7	-0.7
Equity Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	87.2	83.7
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	50.6	44.6
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax	-0.7	-0.6
Fair Value, Nuclear decommissioning trust fund	137.1	127.7
Debt Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	55.4	51
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	3.8	2.5
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	-0.1	-0.7
Fair Value, Nuclear decommissioning trust fund	59.1	52.8
Other Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	2.8	3.4
Fair Value, Nuclear decommissioning trust fund	2.8	3.4
Kansas City Power and Light Company [Member]
Investments in decommissioning trust fund [Line Items]
Fair Value, Nuclear decommissioning trust fund	$199	$183.90	$154.70

Nuclear_Plant_Decommissioning_

Nuclear Plant Decommissioning Trust (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Nuclear decommissioning trust fund [Roll Forward]
Nuclear decommissioning trust fund, beginning balance	$183,900,000	$154,700,000
Contributions to nuclear decommissioning trust fund	3,300,000	3,300,000
Earned income, net of fees	3,600,000	2,700,000
Net realized gains (losses) on nuclear decommissioning trust fund	400,000	1,700,000
Net unrealized gains (losses) on nuclear decommissioning trust fund	7,800,000	21,500,000
Nuclear decommissioning trust fund, ending balance	199,000,000	183,900,000
Wolf Creek [Member]
Nuclear Insurance [Abstract]
Industry aggregate limit on nuclear insurance for property claims including accidental damages	3,200,000,000
Industry aggregate limit on non-nuclear acts of terrorism	1,800,000,000
Amount of insurance against public liability claims resulting from nuclear incidents to full limit of public liability	13,600,000,000
Maximum available commercial insurance	400,000,000
Remaining balance provided through industry wide retrospective assesment program mandated by law	13,200,000,000
Maximum amount able to be assessed to owners	127,300,000
SFP Program-annual amount payable per incident	19,000,000
Amount of decontamination liability, premature decommissioning liability and property damage insurance	2,800,000,000
Premature decommissioning coverage applies only if property damage exceeds this amount and trust funds have been exhausted	500,000,000
Estimated maximum amount of retrospective assessments under the current policies	39,300,000
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	47.00%
Wolf Creek [Member] | Missouri Public Service Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current cost of decommissioning (in 2014 dollars)	765,100,000
Future cost of decommissioning (in 2045 through 2053 dollars)	2,253,100,000
Annual Escalation Factor	3.22%
Annual return on trust assets through 2025	5.68%
Annual return on trusts assets in 2053	2.22%
Wolf Creek [Member] | Kansas Corporation Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current cost of decommissioning (in 2014 dollars)	765,100,000
Future cost of decommissioning (in 2045 through 2053 dollars)	2,201,500,000
Annual Escalation Factor	3.15%
Annual return on trust assets through 2025	6.15%
Annual return on trusts assets in 2053	0.72%
Kansas City Power and Light Company [Member]
Nuclear decommissioning trust fund [Roll Forward]
Nuclear decommissioning trust fund, beginning balance	183,900,000	154,700,000
Contributions to nuclear decommissioning trust fund	3,300,000	3,300,000
Earned income, net of fees	3,600,000	2,700,000
Net realized gains (losses) on nuclear decommissioning trust fund	400,000	1,700,000
Net unrealized gains (losses) on nuclear decommissioning trust fund	7,800,000	21,500,000
Nuclear decommissioning trust fund, ending balance	199,000,000	183,900,000
Kansas City Power and Light Company [Member] | Wolf Creek [Member]
Nuclear Insurance [Abstract]
Maximum amount able to be assessed to owners	59,800,000
SFP Program-annual amount payable per incident	8,900,000
Amount of decontamination liability, premature decommissioning liability and property damage insurance	1,300,000,000
Estimated maximum amount of retrospective assessments under the current policies	18,500,000
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	47.00%
Kansas City Power and Light Company [Member] | Wolf Creek [Member] | Missouri Public Service Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current cost of decommissioning (in 2014 dollars)	359,600,000
Future cost of decommissioning (in 2045 through 2053 dollars)	1,059,000,000
Kansas City Power and Light Company [Member] | Wolf Creek [Member] | Kansas Corporation Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current cost of decommissioning (in 2014 dollars)	359,600,000
Future cost of decommissioning (in 2045 through 2053 dollars)	$1,034,700,000

Regulatory_Matters_Details

Regulatory Matters (Details) (Kansas City Power and Light Company [Member], USD $)	1 Months Ended			12 Months Ended
In Millions, unless otherwise specified	Oct. 31, 2014	Jul. 31, 2014	Dec. 31, 2013	Dec. 31, 2014
Missouri Public Service Commission [Member]
Regulatory Proceedings [Line Items]
Annual revenue increase, requested	$120.90
Return on equity, requested (in hundredths)	10.30%
Rate-making equity ratio, requested (in hundredths)	50.36%
Kansas Corporation Commission [Member]
Regulatory Proceedings [Line Items]
Annual revenue increase, requested			12.1
Revised annual revenue increase, requested				11.5
Annual revenue increase authorized		$11.50

Regulatory_Matters_Asset_Detai

Regulatory Matters Asset (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$1,034.60		$849.70
Taxes recoverable through future rates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	133.4		136.4
Loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	10.9		8.6
Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	2.8		1
Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	55.3		50.8
Pension and post-retirement costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	525.9		401.2
Deferred customer programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	69.6		72
Rate case expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	1.5		4.2
Fuel recovery mechanisms [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	54		23.6
Acquisition transition costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	13.6		23.9
Derivative instruments [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	2.8		0
Iatan No. 1 and Common facilities depreciation and carrying costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	20.2		21
Iatan No. 2 construction accounting costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	43.4		45.3
Kansas property tax surcharge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	6.1		4
Solar Rebates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	86		45.3
Voluntary Separation Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	2.5		3.4
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	6.6		9
Kansas City Power and Light Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	745.7		614.1
Kansas City Power and Light Company [Member] | Taxes recoverable through future rates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	107.1		111
Kansas City Power and Light Company [Member] | Loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	8.1	[1]	7.1
Regulatory amortization period	over the life of the related new debt issuances or the remaining lives of the old debt issuances if no new debt was issued.
Kansas City Power and Light Company [Member] | Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	2.8		1
Kansas City Power and Light Company [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	38.1		34.8
Kansas City Power and Light Company [Member] | Pension and post-retirement costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	430.5	[2]	310
Amount not included in rate base	408.1
Regulatory amortization period	various
Kansas City Power and Light Company [Member] | Deferred customer programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	50.8	[3]	50.2
Amount not included in rate base	22
Regulatory amortization period	various
Kansas City Power and Light Company [Member] | Rate case expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	1.4	[4]	3.6
Regulatory amortization period	various
Kansas City Power and Light Company [Member] | Fuel recovery mechanisms [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	13	[4]	10.8
Regulatory amortization period	various
Kansas City Power and Light Company [Member] | Acquisition transition costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	7	[5]	12.9
Regulatory amortization period	through 2016
Kansas City Power and Light Company [Member] | Derivative instruments [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0.2	[6]	0
Kansas City Power and Light Company [Member] | Iatan No. 1 and Common facilities depreciation and carrying costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	14.7	[7]	15.3
Regulatory amortization period	through 2038
Kansas City Power and Light Company [Member] | Iatan No. 2 construction accounting costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	28.1	[8]	29.3
Regulatory amortization period	through 2058
Kansas City Power and Light Company [Member] | Kansas property tax surcharge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	6.1	[4]	4
Regulatory amortization period	various
Kansas City Power and Light Company [Member] | Solar Rebates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	29.1	[4]	13
Regulatory amortization period	various
Kansas City Power and Light Company [Member] | Voluntary Separation Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	2.5	[9]	3.4
Regulatory amortization period	through 2017
Kansas City Power and Light Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	6.2	[4]	7.7
Regulatory amortization period	various
KCPL Greater Missouri Operations [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	288.9		235.6
KCPL Greater Missouri Operations [Member] | Taxes recoverable through future rates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	26.3		25.4
KCPL Greater Missouri Operations [Member] | Loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	2.8	[1]	1.5
Regulatory amortization period	over the life of the related new debt issuances or the remaining lives of the old debt issuances if no new debt was issued.
KCPL Greater Missouri Operations [Member] | Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0		0
KCPL Greater Missouri Operations [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	17.2		16
KCPL Greater Missouri Operations [Member] | Pension and post-retirement costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	95.4	[2]	91.2
Amount not included in rate base	55.7
Regulatory amortization period	various
KCPL Greater Missouri Operations [Member] | Deferred customer programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	18.8	[10]	21.8
Amount not included in rate base	2.2
Regulatory amortization period	various
KCPL Greater Missouri Operations [Member] | Rate case expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0.1		0.6
KCPL Greater Missouri Operations [Member] | Fuel recovery mechanisms [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	41	[4]	12.8
Regulatory amortization period	various
KCPL Greater Missouri Operations [Member] | Acquisition transition costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	6.6	[5]	11
Regulatory amortization period	through 2016
KCPL Greater Missouri Operations [Member] | Derivative instruments [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	2.6	[6]	0
KCPL Greater Missouri Operations [Member] | Iatan No. 1 and Common facilities depreciation and carrying costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	5.5	[7]	5.7
Regulatory amortization period	through 2038
KCPL Greater Missouri Operations [Member] | Iatan No. 2 construction accounting costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	15.3	[8]	16
Regulatory amortization period	through 2058
KCPL Greater Missouri Operations [Member] | Kansas property tax surcharge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0		0
KCPL Greater Missouri Operations [Member] | Solar Rebates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	56.9	[4]	32.3
Regulatory amortization period	various
KCPL Greater Missouri Operations [Member] | Voluntary Separation Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0		0
KCPL Greater Missouri Operations [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$0.40	[4]	$1.30
Regulatory amortization period	various
[1]	Amortized over the life of the related new debt issuances or the remaining lives of the old debt issuances if no new debt was issued.
[2]	Represents unrecognized gains and losses, prior service and transition costs that will be recognized in future net periodic pension and post-retirement costs, pension settlements amortized over various periods and financial and regulatory accounting method differences that will be eliminated over the life of the pension plans. Of these amounts, $408.1 million and $55.7 million for KCP&L and GMO, respectively, are not included in rate base and are amortized over various periods.
[3]	$22.0 million not included in rate base and amortized over various periods.
[4]	Not included in rate base and amortized over various periods.
[5]	Not included in rate base and amortized through 2016.
[6]	Represents fair value of derivative instruments for commodity contracts. Settlements of the contracts are recognized in the income statement and included in fuel recovery mechanisms.
[7]	Included in rate base and amortized through 2038.
[8]	Included in rate base and amortized through 2058.
[9]	Not included in rate base and amortized through 2017.
[10]	$2.2 million not included in rate base and amortized over various periods.

Regulatory_Matters_Liabilities

Regulatory Matters Liabilities (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Regulatory Liabilities [Line Items]
Regulatory liabilities	$282.70		$264
Emission allowances [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	70.1		74
Asset retirement obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	93.9		86.2
Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	69.7		68.1
Other Regulatory Assets (Liabilities) [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	49		35.7
Kansas City Power and Light Company [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	172		168.3
Kansas City Power and Light Company [Member] | Emission allowances [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	70.1		74
Kansas City Power and Light Company [Member] | Asset retirement obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	93.9		86.2
Kansas City Power and Light Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0		0
Kansas City Power and Light Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	8		8.1
KCPL Greater Missouri Operations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	110.7		95.7
KCPL Greater Missouri Operations [Member] | Emission allowances [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0		0
KCPL Greater Missouri Operations [Member] | Asset retirement obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0		0
KCPL Greater Missouri Operations [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	69.7	[1]	68.1
KCPL Greater Missouri Operations [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$41		$27.60
[1]	Estimated cumulative net provision for future removal costs.

Regulatory_Matters_Regulatory_

Regulatory Matters Regulatory Matters Subsequent Events (Details) (Kansas City Power and Light Company [Member], Kansas Corporation Commission [Member], USD $)	1 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Jan. 31, 2015
Subsequent Event [Line Items]
Annual revenue increase, requested	$12.10
Subsequent Event [Member]
Subsequent Event [Line Items]
Annual revenue increase, requested		$67.30
Return on equity, requested (in hundredths)		10.30%
Rate-making equity ratio, requested (in hundredths)		50.48%

Goodwill_and_Intangible_Assets2

Goodwill and Intangible Assets Goodwill (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Goodwill [Line Items]
Goodwill	$169	$169

Intangibles_Assets_Details

Intangibles Assets (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	$21.60	$17.60
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	24.2
Finite-Lived Intangible Assets, Amortization Expense, Year Two	19
Finite-Lived Intangible Assets, Amortization Expense, Year Three	15
Finite-Lived Intangible Assets, Amortization Expense, Year Four	12.1
Finite-Lived Intangible Assets, Amortization Expense, Year Five	9.2
Kansas City Power and Light Company [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	19.2	14.3
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	21.8
Finite-Lived Intangible Assets, Amortization Expense, Year Two	16.1
Finite-Lived Intangible Assets, Amortization Expense, Year Three	13.9
Finite-Lived Intangible Assets, Amortization Expense, Year Four	11.7
Finite-Lived Intangible Assets, Amortization Expense, Year Five	8.8
Computer Software, Intangible Asset [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	300.2	255.4
Finite-Lived Intangible Assets, Accumulated Amortization	-190.9	-169.9
Computer Software, Intangible Asset [Member] | Kansas City Power and Light Company [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	277.9	231.2
Finite-Lived Intangible Assets, Accumulated Amortization	-175.5	-156.5
Asset Improvements [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	27.4	26.5
Finite-Lived Intangible Assets, Accumulated Amortization	-5.5	-4.9
Asset Improvements [Member] | Kansas City Power and Light Company [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	12.2	11.2
Finite-Lived Intangible Assets, Accumulated Amortization	($1.30)	($1.10)

Asset_Retirement_Obligations_D

Asset Retirement Obligations (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Asset Retirement Obligations, Liability Not Recognized	certain wiring used in Great Plains Energy's and KCP&L's generating stations include asbestos insulation, which would require special handling if disturbed. Due to the inability to reasonably estimate the quantities or the amount of disturbance that will be necessary during dismantlement at the end of the life of a plant, the fair value of this ARO cannot be reasonably estimated at this time. Management will continue to monitor the obligation and will recognize a liability in the period in which sufficient information becomes available to reasonably estimate its fair value.
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	$158.80	$149.30
Accretion	10.3	9.5
Asset Retirement Obligation, Ending Balance	195.9	158.8
Wolf Creek Unit [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Revision in timing and/or estimates	23.9	0
Other Utility Plants [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Revision in timing and/or estimates	2.9	0
Kansas City Power and Light Company [Member]
Asset Retirement Obligations, Description	KCP&L has AROs related to decommissioning Wolf Creek, site remediation of its Spearville Wind Energy Facilities, asbestos abatement and removal of storage tanks, ash ponds and landfills.
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	141.7	133.2
Accretion	9.2	8.5
Asset Retirement Obligation, Ending Balance	177.7	141.7
Kansas City Power and Light Company [Member] | Wolf Creek Unit [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Revision in timing and/or estimates	23.9	0
Kansas City Power and Light Company [Member] | Other Utility Plants [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Revision in timing and/or estimates	$2.90	$0
KCPL Greater Missouri Operations [Member]
Asset Retirement Obligations, Description	GMO has AROs related to asbestos abatement and removal of storage tanks, ash ponds and landfills.

Pension_Plans_and_Other_Employ2

Pension Plans and Other Employee Benefits (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Amounts recognized in the consolidated balance sheets [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities	($2,800,000)		($3,200,000)
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	-508,600,000		-360,500,000
Pension plans with the accumulated benefit obligation in excess of plans assets [Abstract]
Unfunded accumulated benefit obligation for GMO SERP	24,200,000
Segregated assets for GMO SERP	17,500,000
Employee Savings Plans [Abstract]
Defined contribution savings plan, cost of plan	9,700,000		9,600,000		9,200,000
Voluntary Separation Program [Abstract]
Voluntary separation program	0		0		-4,300,000
Kansas City Power and Light Company [Member]
Amounts recognized in the consolidated balance sheets [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities	-1,500,000		-1,900,000
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	-485,400,000		-339,900,000
Employee Savings Plans [Abstract]
Defined contribution savings plan, cost of plan	7,100,000		7,000,000		6,700,000
Voluntary Separation Program [Abstract]
Voluntary separation program	0		0		-4,300,000
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation	1,007,400,000		1,130,500,000
Defined Benefit Plan, Service Cost	36,700,000		41,200,000		35,400,000
Defined Benefit Plan, Interest Cost	50,100,000		47,200,000		48,900,000
Defined Benefit Plan, Contributions by Plan Participants	0		0
Defined Benefit Plan, Plan Amendments	0		300,000
Actuarial (gain) loss	181,100,000		-118,400,000
Defined Benefit Plan, Benefits Paid	-49,000,000		-52,900,000
Defined Benefit Plan, Settlements, Benefit Obligation	-39,500,000		-40,500,000
Defined Benefit Plan, Benefit Obligation	1,186,800,000		1,007,400,000		1,130,500,000
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of the year	703,000,000		666,400,000
Actual return on plan assets	47,200,000		70,900,000
Defined benefit plan, contributions by employer and participants	66,200,000		57,400,000
Defined benefit plan benefits paid portion paid from plan assets	-46,900,000		-51,200,000
Defined Benefit Plan, Settlements, Plan Assets	-39,500,000		-40,500,000
Fair value of plan assets at end of the year	730,000,000		703,000,000		666,400,000
Funded status at end of year	-456,800,000		-304,400,000
Amounts recognized in the consolidated balance sheets [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities	-1,900,000		-2,300,000
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	-454,900,000		-302,100,000
Defined Benefit Plan Amounts Recognized in Balance Sheet before Regulatory Treatment	-456,800,000		-304,400,000
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or regulatory asset/liability	500,500,000		368,300,000
Defined Benefit Plan, Amounts Recognized in Balance Sheet	43,700,000		63,900,000
Amounts in accumulated other comprehensive income or regulatory asset/liability not yet recognized as a component of net periodic benefit cost [Abstract]
Defined Benefit Plan Accumulated Other Comprehensive Income Or Regulatory Asset/Liability Net Gains/Losses Before Tax	273,500,000		147,700,000
Defined Benefit Plan Accumulated Other Comprehensive Income Or Regulatory Asset/Liability Net Prior Service Cost Credit Before Tax	4,700,000		5,600,000
Defined Benefit Plan Accumulated Other Comprehensive Income Or Regulatory Asset/Liability Net Transition Obligation Before Tax	0		0
Defined Benefit Plan Accumulated Other Comprehensive Income Other Before Tax	222,300,000		215,000,000
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or regulatory asset/liability	500,500,000		368,300,000
Components of net periodic benefit costs [Abstract]
Defined Benefit Plan, Service Cost	36,700,000		41,200,000		35,400,000
Defined Benefit Plan, Interest Cost	50,100,000		47,200,000		48,900,000
Defined Benefit Plan, Expected Return on Plan Assets	-50,200,000		-47,100,000		-42,900,000
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	900,000		2,000,000		4,500,000
Defined Benefit Plan, Amortization of (Gains) Losses	50,000,000		54,300,000		44,500,000
Defined Benefit Plan, Amortization of Transition Obligations (Assets)	0		0		0
Settlement charges	8,500,000		4,900,000		800,000
Net periodic benefit costs before regulatory adjustment	96,000,000		102,500,000		91,200,000
Defined benefit plan, regulatory adjustment	-11,300,000		-16,800,000		-15,500,000
Defined Benefit Plan, Net Periodic Benefit Cost	84,700,000		85,700,000		75,700,000
Other Changes In Plan Assets And Benefit Obligations Recognized In Other Comprehensive Income Regulatory Assets/Liabilities [Abstract]
Net (gain) loss arising during period	175,800,000		-147,000,000		97,900,000
Amortization of net gains (losses) included in net periodic benefit costs	-50,000,000		-54,300,000		-44,500,000
Prior service cost	0		300,000		1,100,000
Amortization of prior service cost	-900,000		-2,000,000		-4,500,000
Amortization of transition obligation	0		0		0
Other regulatory activity	7,300,000		11,800,000		17,700,000
Total Recognized In Other Comprehensive Income Or Regulatory Asset/Liability	132,200,000		-191,200,000		67,700,000
Total Recognized In Net Periodic Benefit Costs And Other Comprehensive Income Or Regulatory Asset/Liability	216,900,000		-105,500,000		143,400,000
Estimated prior service cost that will be amortized in the next fiscal year	800,000
Net (gain) loss for the defined benefit plans that will be amortized in the next fiscal year	51,400,000
Length Of Time For Amortization Of Net Actuarial Gains And Losses For Financial Reporting Purposes	rolling five-year average
Length Of Time For Amortization Of Net Actuarial Gains And Losses For Regulatory Reporting Purposes	ten years
Accumulated benefit obligation (ABO) for all defined benefit plans	1,036,800,000		889,200,000
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Benefit Obligation	1,186,800,000		1,007,400,000
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets	730,000,000		703,000,000
Pension plans with the accumulated benefit obligation in excess of plans assets [Abstract]
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Accumulated Benefit Obligation	1,036,800,000		889,200,000
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets	730,000,000		703,000,000
Weighted average assumptions used to determine the benefit obligation [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.22%		5.03%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	3.62%		3.69%
Defined Benefit Plan, Assumptions Used in Calculations, Narrative Description	The expected long-term rate of return on plan assets represents Great Plains Energy's estimate of the long-term return on plan assets and is based on historical and projected rates of return for current and planned asset classes in the plans' investment portfolios. Assumed projected rates of return for each asset class were selected after analyzing historical experience and future expectations of the returns of various asset classes. Based on the target asset allocation for each asset class, the overall expected rate of return for the portfolios was developed and adjusted for the effect of projected benefits paid from plan assets and future plan contributions.
Weighted average assumptions used to determine net costs [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	5.03%		4.17%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	7.24%		7.24%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.69%		3.69%
Contribute to plans in next year	78,900,000
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	76,500,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	74,900,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	76,700,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	78,200,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	80,200,000
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	420,600,000
Defined Benefit Plan, Target Allocation Percentage	The portfolios are invested, and periodically rebalanced, to achieve targeted allocations of approximately 33% U.S. large cap and small cap equity securities, 20% international equity securities, 35% fixed income securities, 7% real estate, 1% commodities and 4% hedge funds.
Defined Benefit Plan, Investment Strategies, Investment Fund Category	The investment strategy supports the objective of the fund, which is to earn the highest possible return on plan assets within a reasonable and prudent level of risk.
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation	160,500,000		186,500,000
Defined Benefit Plan, Service Cost	3,700,000		4,400,000		3,300,000
Defined Benefit Plan, Interest Cost	7,900,000		7,700,000		7,800,000
Defined Benefit Plan, Contributions by Plan Participants	6,800,000		6,200,000
Defined Benefit Plan, Plan Amendments	0		-6,000,000
Actuarial (gain) loss	-300,000		-26,100,000
Defined Benefit Plan, Benefits Paid	-13,400,000		-12,200,000
Defined Benefit Plan, Settlements, Benefit Obligation	0		0
Defined Benefit Plan, Benefit Obligation	165,200,000		160,500,000		186,500,000
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of the year	101,200,000		90,300,000
Actual return on plan assets	4,100,000		-2,000,000
Defined benefit plan, contributions by employer and participants	18,600,000		25,000,000
Defined benefit plan benefits paid portion paid from plan assets	-13,300,000		-12,100,000
Defined Benefit Plan, Settlements, Plan Assets	0		0
Fair value of plan assets at end of the year	110,600,000		101,200,000		90,300,000
Funded status at end of year	-54,600,000		-59,300,000
Amounts recognized in the consolidated balance sheets [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities	-900,000		-900,000
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	-53,700,000		-58,400,000
Defined Benefit Plan Amounts Recognized in Balance Sheet before Regulatory Treatment	-54,600,000		-59,300,000
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or regulatory asset/liability	26,100,000		35,300,000
Defined Benefit Plan, Amounts Recognized in Balance Sheet	-28,500,000		-24,000,000
Amounts in accumulated other comprehensive income or regulatory asset/liability not yet recognized as a component of net periodic benefit cost [Abstract]
Defined Benefit Plan Accumulated Other Comprehensive Income Or Regulatory Asset/Liability Net Gains/Losses Before Tax	17,500,000		19,200,000
Defined Benefit Plan Accumulated Other Comprehensive Income Or Regulatory Asset/Liability Net Prior Service Cost Credit Before Tax	13,500,000		16,600,000
Defined Benefit Plan Accumulated Other Comprehensive Income Or Regulatory Asset/Liability Net Transition Obligation Before Tax	200,000		400,000
Defined Benefit Plan Accumulated Other Comprehensive Income Other Before Tax	-5,100,000		-900,000
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or regulatory asset/liability	26,100,000		35,300,000
Components of net periodic benefit costs [Abstract]
Defined Benefit Plan, Service Cost	3,700,000		4,400,000		3,300,000
Defined Benefit Plan, Interest Cost	7,900,000		7,700,000		7,800,000
Defined Benefit Plan, Expected Return on Plan Assets	-2,600,000		-2,000,000		-1,800,000
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	3,100,000		7,200,000		7,100,000
Defined Benefit Plan, Amortization of (Gains) Losses	-100,000		1,700,000		-200,000
Defined Benefit Plan, Amortization of Transition Obligations (Assets)	200,000		200,000		1,100,000
Settlement charges	0		0		0
Net periodic benefit costs before regulatory adjustment	12,200,000		19,200,000		17,300,000
Defined benefit plan, regulatory adjustment	4,300,000		-2,400,000		1,500,000
Defined Benefit Plan, Net Periodic Benefit Cost	16,500,000		16,800,000		18,800,000
Other Changes In Plan Assets And Benefit Obligations Recognized In Other Comprehensive Income Regulatory Assets/Liabilities [Abstract]
Net (gain) loss arising during period	-1,800,000		-22,100,000		27,100,000
Amortization of net gains (losses) included in net periodic benefit costs	100,000		-1,700,000		200,000
Prior service cost	0		-6,000,000		0
Amortization of prior service cost	-3,100,000		-7,200,000		-7,100,000
Amortization of transition obligation	-200,000		-200,000		-1,100,000
Other regulatory activity	-4,200,000		2,100,000		-1,200,000
Total Recognized In Other Comprehensive Income Or Regulatory Asset/Liability	-9,200,000		-35,100,000		17,900,000
Total Recognized In Net Periodic Benefit Costs And Other Comprehensive Income Or Regulatory Asset/Liability	7,300,000		-18,300,000		36,700,000
Estimated prior service cost that will be amortized in the next fiscal year	3,100,000
Net (gain) loss for the defined benefit plans that will be amortized in the next fiscal year	200,000
Transition costs for the defined benefit plans that will be amortized in the next fiscal year	200,000
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Benefit Obligation	165,200,000		160,500,000
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets	110,600,000		101,200,000
Weighted average assumptions used to determine the benefit obligation [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.14%		4.92%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	3.50%		3.50%
Weighted average assumptions used to determine net costs [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.92%		4.13%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	2.70%	[1]	2.62%	[1]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.50%		3.50%
Contribute to plans in next year	10,200,000
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	7,500,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	8,100,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	8,600,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	9,000,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	9,400,000
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	49,700,000
Defined Benefit Plan, Investment Strategies, Investment Fund Category	The investment strategy supports the objective of the funds, which is to preserve capital, maintain sufficient liquidity and earn a consistent rate of return.
Health care cost trend (in hundredths)	7.00%		7.00%
Health care cost rate declining through	2025
Ultimate cost trend rate (in hundredths)	4.50%
Effect on total service and interest component, increase	900,000
Effect on total service and interest component, decrease	-1,100,000
Effect on post-retirement benefit obligation, increase	7,400,000
Effect on post-retirement benefit obligation, decrease	($6,100,000)
[1]	after tax

Pension_Plans_and_Other_Employ3

Pension Plans and Other Employee Benefits Pension Plans Fair Value (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	$730,000,000		$703,000,000		$666,400,000
Pension Plans, Defined Benefit [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	38,900,000	[1]	49,100,000	[1]
Pension Plans, Defined Benefit [Member] | Real Estate [Member] | Institutional Common Collective Trust Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	12,700,000		32,600,000
Pension Plans, Defined Benefit [Member] | Real Estate [Member] | Real Estate Investment Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	7,700,000		0
Pension Plans, Defined Benefit [Member] | Real Estate [Member] | Limited Partnerships [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	18,500,000		16,500,000
Pension Plans, Defined Benefit [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	24,100,000	[2]	23,100,000	[2]
Pension Plans, Defined Benefit [Member] | US Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	235,200,000	[3]	193,700,000	[3]
Pension Plans, Defined Benefit [Member] | US Equity Securities [Member] | Traded Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	78,100,000		80,500,000
Pension Plans, Defined Benefit [Member] | US Equity Securities [Member] | Institutional Common Collective Trust Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	31,600,000		113,200,000
Pension Plans, Defined Benefit [Member] | US Equity Securities [Member] | Common Stock and Exchange Traded Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	125,500,000
Pension Plans, Defined Benefit [Member] | International Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	147,300,000	[4]	167,100,000	[4]
Pension Plans, Defined Benefit [Member] | International Equity Securities [Member] | Traded Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	38,600,000		39,900,000
Pension Plans, Defined Benefit [Member] | International Equity Securities [Member] | Institutional Common Collective Trust Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	38,600,000		127,200,000
Pension Plans, Defined Benefit [Member] | International Equity Securities [Member] | American Depository Receipts Global Depository Receipts and Ordinary Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	70,100,000
Pension Plans, Defined Benefit [Member] | Commodity Contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	5,900,000	[5]	34,800,000	[5]
Pension Plans, Defined Benefit [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	66,100,000	[6]	181,300,000	[6]
Pension Plans, Defined Benefit [Member] | Fixed Income Funds [Member] | Traded Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	22,300,000		27,100,000
Pension Plans, Defined Benefit [Member] | Fixed Income Funds [Member] | Institutional Common Collective Trust Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	43,800,000		154,200,000
Pension Plans, Defined Benefit [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	44,200,000		2,600,000
Pension Plans, Defined Benefit [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	21,000,000		17,100,000
Pension Plans, Defined Benefit [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	109,000,000	[7]	25,600,000
Pension Plans, Defined Benefit [Member] | US corporate bonds [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	100,300,000		20,100,000
Pension Plans, Defined Benefit [Member] | US corporate bonds [Member] | Collateralized Mortgage Obligation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	4,000,000		3,600,000
Pension Plans, Defined Benefit [Member] | US corporate bonds [Member] | Asset-backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	4,700,000		1,900,000
Pension Plans, Defined Benefit [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	13,600,000		2,300,000
Pension Plans, Defined Benefit [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	16,700,000		3,000,000
Pension Plans, Defined Benefit [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	8,000,000		3,300,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	402,900,000		153,100,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	7,700,000	[1]	0	[1]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	[2]	0	[2]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | US Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	203,600,000	[3]	80,500,000	[3]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | International Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	108,400,000	[4]	39,900,000	[4]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Commodity Contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	[5]	0	[5]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	22,300,000	[6]	27,100,000	[6]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	44,200,000		2,600,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	[7]	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	16,700,000		3,000,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	278,100,000		483,100,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	6,300,000	[1]	5,400,000	[1]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	[2]	0	[2]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | US Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	31,600,000	[3]	113,200,000	[3]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | International Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	38,900,000	[4]	127,200,000	[4]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Commodity Contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	5,900,000	[5]	34,800,000	[5]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	43,800,000	[6]	154,200,000	[6]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	21,000,000		17,100,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	109,000,000	[7]	25,600,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	13,600,000		2,300,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	8,000,000		3,300,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	49,000,000		66,800,000
Actual return on plan assets [Abstract]
Balance at beginning of period	66,800,000		60,000,000
Relating to assets still held	4,100,000		6,100,000
Relating to assets sold	1,200,000
Purchase, sales and settlements	-23,100,000		700,000
Balance at end of period	49,000,000		66,800,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	24,900,000	[1]	43,700,000	[1]
Actual return on plan assets [Abstract]
Balance at beginning of period	43,700,000		38,400,000
Relating to assets still held	3,100,000		4,600,000
Relating to assets sold	1,200,000
Purchase, sales and settlements	-23,100,000		700,000
Balance at end of period	24,900,000		43,700,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	24,100,000	[2]	23,100,000	[2]
Actual return on plan assets [Abstract]
Balance at beginning of period	23,100,000		21,600,000
Relating to assets still held	1,000,000		1,500,000
Relating to assets sold	0
Purchase, sales and settlements	0		0
Balance at end of period	24,100,000		23,100,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | US Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	[3]	0	[3]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | International Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	[4]	0	[4]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Commodity Contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	[5]	0	[5]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	[6]	0	[6]
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	[7]	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	110,600,000		101,200,000		90,300,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	3,200,000		2,200,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	73,000,000	[8]	74,600,000	[8]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Funds [Member] | Traded Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	200,000		200,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Funds [Member] | Institutional Common Collective Trust Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	72,800,000		74,400,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	2,700,000		1,500,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	4,900,000		4,400,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	13,000,000	[9]	8,600,000	[9]
Other Postretirement Benefit Plans, Defined Benefit [Member] | US corporate bonds [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	10,300,000		7,100,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | US corporate bonds [Member] | Collateralized Mortgage Obligation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	800,000		300,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | US corporate bonds [Member] | Asset-backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	1,900,000		1,200,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	1,500,000		1,000,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	10,400,000		8,600,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	1,900,000		300,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	16,500,000		12,500,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	3,200,000		2,200,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	200,000	[8]	200,000	[8]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	2,700,000		1,500,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	[9]	0	[9]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	10,400,000		8,600,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	94,100,000		88,700,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	72,800,000	[8]	74,400,000	[8]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	4,900,000		4,400,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	13,000,000	[9]	8,600,000	[9]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	1,500,000		1,000,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	1,900,000		300,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	[8]	0	[8]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	[9]	0	[9]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	$0		$0
[1]	At December 31, 2014 and 2013, this category is comprised of $7.7 million and none, respectively, of traded real estate investment trusts, $12.7 million and $32.6 million, respectively, of institutional common/collective trust funds and $18.5 million and $16.5 million, respectively, of a limited partnership valued at NAV on a quarterly basis.
[2]	This category is comprised of closely-held limited partnerships valued at NAV on a quarterly basis.
[3]	At December 31, 2014 and 2013, this category is comprised of $78.1 million and $80.5 million, respectively, of traded mutual funds valued at daily listed prices and $31.6 million and $113.2 million, respectively, of institutional common/collective trust funds valued at Net Asset Value (NAV) per share. At December 31, 2014, this category also included $125.5 million of traded common stocks and exchange traded funds.
[4]	At December 31, 2014 and 2013, this category is comprised of $38.6 million and $39.9 million, respectively, of traded mutual funds valued at daily listed prices and $38.6 million and $127.2 million, respectively, of institutional common/collective trust funds valued at daily NAV per share. At December 31, 2014, this category also included $70.1 million of traded American depository receipts, global depository receipts and ordinary shares.
[5]	This category is comprised of institutional common/collective trust funds valued at daily NAV per share.
[6]	At December 31, 2014 and 2013, this category is comprised of $22.3 million and $27.1 million, respectively, of traded mutual funds valued at daily listed prices and $43.8 million and $154.2 million, respectively, of institutional common/collective trust funds valued at daily NAV per share.
[7]	At December 31, 2014 and 2013, this category is comprised of $100.3 million and $20.1 million, respectively, of corporate bonds, $4.0 million and $3.6 million, respectively, of collateralized mortgage obligations and $4.7 million and $1.9 million, respectively, of other asset-backed securities.
[8]	At December 31, 2014 and 2013, this category is comprised of $72.8 million and $74.4 million, respectively, of an institutional common/collective trust fund valued at daily NAV per share and $0.2 million of traded mutual funds valued at daily listed prices.
[9]	At December 31, 2014 and 2013, this category is comprised of $10.3 million and $7.1 million, respectively, of corporate bonds, $0.8 million and $0.3 million, respectively, of collateralized mortgage obligations and $1.9 million and $1.2 million, respectively, of other asset-backed securities.

Equity_Compensation_Details

Equity Compensation (Details) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares of common shares authorized (in shares)	8,000,000
Equity compensation expense	$9.90		$5.60		$3.30
Income tax benefit	3.6		1.9		1.4
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)	214,946
Earned (in shares)	-107,741
Performance adjustment (in shares)	-271
Forfeited (in shares)	-2,927
Ending balance (in shares)	534,016		430,009
Weighted average beginning balance (in dollars per share)	$23.52	[1]
Weighted average granted (in dollars per share)	$28.78	[1]	$24.17		$19.37
Weighted average earned (in dollars per share)	$26.14	[1]
Weighted average forfeited (in dollars per share)	$25.73	[1]
Weighted average ending balance (in dollars per share)	$25.11	[1]	$23.52	[1]
Total unrecognized compensation expense	8.8
Remaining weighted-average contractual term (in years)	1 year 2 months
Fair value of performance shares earned and paid	2.8		2.4		0
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares)	288,537
Granted (in shares)	81,290
Vested (in shares)	-101,174
Forfeited (in shares)	-1,263
Ending balance (in shares)	267,390		288,537
Weighted average beginning balance (in dollars per share)	$20.18	[1]
Weighted average granted (in dollars per share)	$25.70	[1]	$22.47		$19.75
Weighted average vested (in dollars per share)	$18.96	[1]
Weighted average forfeited (in dollars per share)	$24.16	[1]
Weighted average ending balance (in dollars per share)	$22.31	[1]	$20.18	[1]
Total unrecognized compensation expense	2.3
Total fair value of shares vested	1.9		1.2		3.3
Remaining weighted-average contractual term (in years)	1 year 1 month
Kansas City Power and Light Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	6.9		4		2.3
Income tax benefit	$2.40		$1.30		$1
[1]	weighted-average

Equity_Compensation_Equity_Com

Equity Compensation Equity Compensation Deferred Directors (Details) (Director [Member], Director Deferred Share Units [Member], USD $)	12 Months Ended
	Dec. 31, 2014
Director [Member] | Director Deferred Share Units [Member]
Director deferred share units [Roll Forward]
Director deferred share units, beginning balance (in shares)	90,120
Director deferred share units, issued (in shares)	20,621
Director deferred share units, ending balance (in shares)	110,741
Weighted-average grant date fair value, director deferred share units, beginning balance (in dollars per share)	$20.94	[1]
Weighted-average grant date fair value, director deferred share units, issued (in dollars per share)	$26.53	[1]
Weighted-average grant date fair value, director deferred share units, ending balance (in dollars per share)	$21.98	[1]
[1]	weighted-average

Shortterm_Borrowings_and_Short1

Short-term Borrowings and Short-term Bank Lines of Credit (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Short-term Debt [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$139,500,000
Amount of outstanding cash borrowings	4,000,000	9,000,000
Commercial paper outstanding	358,300,000	108,200,000
Parent Company [Member]
Short-term Debt [Line Items]
Amount of outstanding cash borrowings	4,000,000	9,000,000
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	31-Oct-19
Maximum borrowing capacity with transfer of unused commitments	400,000,000
Line of Credit Facility, Covenant Terms	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.
Line of Credit Facility, Covenant Compliance	in compliance
Amount of outstanding cash borrowings	4,000,000	9,000,000
Weighted-average interest rate from outstanding borrowings	1.69%	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	358,300,000	93,200,000
Weighted-average interest rate from outstanding borrowings	0.48%	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	31-Oct-19
Maximum transfer of unused commitments	200,000,000
Line of Credit Facility, Covenant Terms	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.
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		15,000,000
Weighted-average interest rate from outstanding borrowings		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	31-Oct-19
Maximum transfer of unused commitments	200,000,000
Line of Credit Facility, Covenant Terms	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.
Line of Credit Facility, Covenant Compliance	in compliance
Amount of outstanding cash borrowings	0	0
Amount of letters of credit outstanding	$3,200,000	$16,400,000

LongTerm_Debt_Details

Long-Term Debt (Details) (USD $)	12 Months Ended					1 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Jan. 31, 2014
Debt Instrument [Line Items]
Current maturities	($15.10)		($1.10)
Long-term debt excluding current maturities	3,488		3,515.70
Amortization of Financing Costs	4.8		5.7		5.5
Repayments of Long-term Debt	13.4		265.3		513.8
Long-term Debt, Fiscal Year Maturity [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	15.1
Long-term Debt, Maturities, Repayments of Principal in Year Two	1.1
Long-term Debt, Maturities, Repayments of Principal in Year Three	382.1
Long-term Debt, Maturities, Repayments of Principal in Year Four	351.1
Long-term Debt, Maturities, Repayments of Principal in Year Five	401.1
Kansas City Power and Light Company [Member]
Debt Instrument [Line Items]
Current maturities	-14		0
Unamortized discount	-3.8		-4.1
Long-term debt excluding current maturities	2,298.50		2,312.20
Amortization of Financing Costs	3		3.2		2.9
Repayments of Long-term Debt	0		2.6		12.7
Long-term Debt, Fiscal Year Maturity [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	14
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-term Debt, Maturities, Repayments of Principal in Year Three	281
Long-term Debt, Maturities, Repayments of Principal in Year Four	350
Long-term Debt, Maturities, Repayments of Principal in Year Five	400
Kansas City Power and Light Company [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Principal outstanding	596.4		596.4
Kansas City Power and Light Company [Member] | Secured Debt [Member] | General Mortgage bonds EIRR due 2015-2035 [Member]
Debt Instrument [Line Items]
Principal outstanding	146.4	[1]	146.4	[1]
Debt Instrument Maturity Date Range Start	31-Dec-15
Debt Instrument Maturity Date Range End	31-Dec-35
Long-term Debt, Weighted Average Interest Rate	2.95%
Kansas City Power and Light Company [Member] | Secured Debt [Member] | General Mortgage bonds Series 2009A due 2019 [Member]
Debt Instrument [Line Items]
Principal outstanding	400	[2]	400	[2]
Debt Instrument, Maturity Date	31-Dec-19
Interest rates (in hundredths)	7.15%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	8.59%
Kansas City Power and Light Company [Member] | Secured Debt [Member] | General Mortgage bonds EIRR series 2005 due 2035 [Member]
Debt Instrument [Line Items]
Principal outstanding	50		50
Debt Instrument, Maturity Date	31-Dec-35
Interest rates (in hundredths)	4.65%
Kansas City Power and Light Company [Member] | Secured Debt [Member] | Secured EIRR Bonds Series 2005 [Member]
KCPL Municipal Bond Insurance Policies [Abstract]
Principal outstanding covered by insurance policies	35.9
Insurance Agreement Covenant Description	The insurance agreements contain a covenant that the indebtedness to total capitalization ratio of KCP&L and its consolidated subsidiaries will not be greater than 0.68 to 1.00.
Insurance Agreement Covenant Compliance	in compliance
Insurance Agreement Covenant Indebtedness To Total Capitalization Ratio Maximum	75.00%
Proportion Of Secured Debt To Total Indebtedness Based On Bond Ratings Maximum In Hundredths	50.00%
Aggregate Amount Of Outstanding General Mortgage Bonds As Percentage Of Total Capitalization Maximum In Hundredths	10.00%
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior notes due 2017 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding	250	[2]	250	[2]
Debt Instrument, Maturity Date	31-Dec-17
Interest rates (in hundredths)	5.85%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	5.72%
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior notes due 2018 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding	350	[2]	350	[2]
Debt Instrument, Maturity Date	31-Dec-18
Interest rates (in hundredths)	6.38%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	7.49%
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior Notes due 2023 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding	300		300
Debt Instrument, Maturity Date	31-Dec-23
Interest rates (in hundredths)	3.15%
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior notes due 2035 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding	250	[2]	250	[2]
Debt Instrument, Maturity Date	31-Dec-35
Interest rates (in hundredths)	6.05%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	5.78%
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior Notes Due 2041 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding	400		400
Debt Instrument, Maturity Date	31-Dec-41
Interest rates (in hundredths)	5.30%
Kansas City Power and Light Company [Member] | Unsecured Debt [Member] | EIRR Bonds Series 2007A and 2007B due 2035 [Member]
Debt Instrument [Line Items]
Principal outstanding	146.5	[3]	146.5	[3]
Debt Instrument, Maturity Date	31-Dec-35
Variable rate (in hundredths)	0.05%
Kansas City Power and Light Company [Member] | Unsecured Debt [Member] | EIRR bonds 2.875 percent Series 2008 [Member]
Debt Instrument [Line Items]
Principal outstanding	23.4		23.4
Debt Instrument, Maturity Date	31-Dec-38
Interest rates (in hundredths)	2.88%
Kansas City Power and Light Company [Member] | Unsecured Debt [Member] | Unsecured EIRR Bonds Series 2005 [Member]
KCPL Municipal Bond Insurance Policies [Abstract]
Principal outstanding covered by insurance policies	50
Insurance Agreement Covenant Description	The insurance agreements contain a covenant that the indebtedness to total capitalization ratio of KCP&L and its consolidated subsidiaries will not be greater than 0.68 to 1.00.
Insurance Agreement Covenant Compliance	in compliance
Insurance Agreement Covenant Indebtedness To Total Capitalization Ratio Maximum	75.00%
Proportion Of Secured Debt To Total Indebtedness Based On Bond Ratings Maximum In Hundredths	50.00%
Aggregate Amount Of Outstanding General Mortgage Bonds As Percentage Of Total Capitalization Maximum In Hundredths	10.00%
KCPL Greater Missouri Operations [Member] | Secured Debt [Member] | First Mortgage Bonds due through 2021 [Member]
Debt Instrument [Line Items]
Principal outstanding	7.9		9
Debt Instrument Maturity Date Range Start	31-Dec-15
Debt Instrument Maturity Date Range End	31-Dec-21
Interest rates (in hundredths)	9.44%
KCPL Greater Missouri Operations [Member] | Senior Notes [Member] | Senior notes 8.27 percent series due 2021 [Member]
Debt Instrument [Line Items]
Principal outstanding	80.9		80.9
Debt Instrument, Maturity Date	31-Dec-21
Interest rates (in hundredths)	8.27%
KCPL Greater Missouri Operations [Member] | Senior Notes [Member] | Senior Notes Series A due 2025 [Member]
Debt Instrument [Line Items]
Principal outstanding	125		125
Debt Instrument, Maturity Date	31-Dec-25
Interest rates (in hundredths)	3.49%
GMO Senior Notes [Abstract]
Debt Instrument, Covenant Description	GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the agreement, not greater than 0.65 to 1.00 at all times. In addition, GMO's priority debt, as defined in the agreement, cannot exceed 15% of consolidated tangible net worth, as defined in the agreement
Debt Instrument, Covenant Compliance	in compliance
KCPL Greater Missouri Operations [Member] | Senior Notes [Member] | Senior Notes Series B due 2033 [Member]
Debt Instrument [Line Items]
Principal outstanding	75		75
Debt Instrument, Maturity Date	31-Dec-33
Interest rates (in hundredths)	4.06%
GMO Senior Notes [Abstract]
Debt Instrument, Covenant Description	GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the agreement, not greater than 0.65 to 1.00 at all times. In addition, GMO's priority debt, as defined in the agreement, cannot exceed 15% of consolidated tangible net worth, as defined in the agreement.
Debt Instrument, Covenant Compliance	in compliance
KCPL Greater Missouri Operations [Member] | Senior Notes [Member] | Senior Notes Series C due 2043 [Member]
Debt Instrument [Line Items]
Principal outstanding	150		150
Debt Instrument, Maturity Date	31-Dec-43
Interest rates (in hundredths)	4.74%
GMO Senior Notes [Abstract]
Debt Instrument, Covenant Description	GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the agreement, not greater than 0.65 to 1.00 at all times. In addition, GMO's priority debt, as defined in the agreement, cannot exceed 15% of consolidated tangible net worth, as defined in the agreement.
Debt Instrument, Covenant Compliance	in compliance
KCPL Greater Missouri Operations [Member] | Medium-term Notes [Member] | Medium term notes 7.33 percent series due 2023 [Member]
Debt Instrument [Line Items]
Principal outstanding	3		3
Debt Instrument, Maturity Date	31-Dec-23
Interest rates (in hundredths)	7.33%
KCPL Greater Missouri Operations [Member] | Medium-term Notes [Member] | Medium term notes 7.17 percent series due 2023 [Member]
Debt Instrument [Line Items]
Principal outstanding	7		7
Debt Instrument, Maturity Date	31-Dec-23
Interest rates (in hundredths)	7.17%
KCPL Greater Missouri Operations [Member] | Unsecured Debt [Member] | Pollution control bonds Wamego Series 1996 due 2026 [Member]
Debt Instrument [Line Items]
Principal outstanding	0		7.3
Repayments of Long-term Debt						7.3
KCPL Greater Missouri Operations [Member] | Unsecured Debt [Member] | Pollution control bonds state environmental 1993 due 2028 [Member]
Debt Instrument [Line Items]
Principal outstanding	0		5
Repayments of Long-term Debt						5
Parent Company [Member]
Debt Instrument [Line Items]
Long-term debt excluding current maturities	741.8		742.4
Repayments of Long-term Debt	0		250		0
Parent Company [Member] | Senior Notes [Member] | Senior notes due 2017 [Member]
Debt Instrument [Line Items]
Principal outstanding	100	[2]	100	[2]
Debt Instrument, Maturity Date	31-Dec-17
Interest rates (in hundredths)	6.88%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	7.33%
Parent Company [Member] | Senior Notes [Member] | Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Principal outstanding	350		350
Debt Instrument, Maturity Date	31-Dec-21
Interest rates (in hundredths)	4.85%
Parent Company [Member] | Senior Notes [Member] | Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Principal outstanding	287.5		287.5
Debt Instrument, Maturity Date	31-Dec-22
Interest rates (in hundredths)	5.29%
Other Consolidated Entities [Member]
Debt Instrument [Line Items]
Current maturities	-1.1		-1.1
Unarmortized discount and premium, net	4.3		4.9
Amortization of Financing Costs	$1.80		$2.50		$2.60
[1]	Weighted-average interest rates at December 31, 2014
[2]	Rate after amortizing gains/losses recognized in OCI on settlements of interest rate hedging instruments
[3]	Variable rate

Assets_Held_for_Sale_Assets_He1

Assets Held for Sale Assets Held for Sale (Details) (USD $)	1 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Jan. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets held for sale		$0	$36.20
Proceeds from sale of assets	37.7	37.7	0	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	$0

Common_Shareholders_Equity_Det

Common Shareholders' Equity (Details) (USD $)	12 Months Ended
In Billions, except Share data in Millions, unless otherwise specified	Dec. 31, 2014
Common Shareholders' Equity [Line Items]
Shares authorized under the Dividend Reinvestment and Direct Stock Purchase Plan (in shares)	6
Number of shares available for grant under the Dividend Reinvestment and Direct Stock Purchase Plan (in shares)	1.2
Shares registered under the defined contribution savings plan (in shares)	14.3
Number of shares available under the defined contribution savings plan (in shares)	1.3
Restrictions on the payment of common stock dividends	Great Plains Energy's articles of incorporation restrict the payment of common stock dividends in the event common equity is 25% or less of total capitalization. In addition, if preferred stock dividends are not declared and paid when scheduled, Great Plains Energy could not declare or pay common stock dividends or purchase any common shares. If the unpaid preferred stock dividends equal four or more full quarterly dividends, the preferred shareholders, voting as a single class, could elect the smallest number of directors necessary to constitute a majority of the full Board. Certain conditions in the MPSC and KCC orders authorizing the holding company structure require Great Plains Energy and KCP&L to maintain consolidated common equity of at least 30% and 35%, respectively, of total capitalization (including only the amount of short-term debt in excess of the amount of construction work in progress). Under the Federal Power Act, KCP&L and GMO generally can pay dividends only out of retained earnings. The revolving credit agreements of Great Plains Energy, KCP&L and GMO and the note purchase agreement for GMO's Series A, B and C Senior Notes contain a covenant requiring the respective company to maintain a consolidated indebtedness to consolidated total capitalization ratio of not more than 0.65 to 1.00.
Restricted net assets of subsidiaries	$2.80

Preferred_Stock_Details

Preferred Stock (Details) (USD $)	Dec. 31, 2014
In Millions, except Share data, unless otherwise specified
No Par Preference Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	11,000,000
Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	390,000
Preferred Stock, Shares Outstanding	390,000
Preferred Stock, Par or Stated Value Per Share	100
Preferred Stock, Value, Outstanding	39
Cumulative No Par Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	1,600,000
Minimum [Member] | Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Optional Redemption Percentage of Par Value	101.00%
Maximum [Member] | Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Optional Redemption Percentage of Par Value	103.70%

Commitments_and_Contingencies_1

Commitments and Contingencies Commitments and Contingencies Contractual Commitments (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Lease Expense [Abstract]
Lease expense	$16	$18.50	$21.80
Operating Leases [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	14.2
Operating Leases, Future Minimum Payments, Due in Two Years	10
Operating Leases, Future Minimum Payments, Due in Three Years	9.7
Operating Leases, Future Minimum Payments, Due in Four Years	9.7
Operating Leases, Future Minimum Payments, Due in Five Years	9
Operating Leases, Future Minimum Payments, Due Thereafter	129.5
Operating Leases, Future Minimum Payments Due, Total	182.1
Capital Leases [Abstract]
Capital Leases, Future Minimum Payments Due, Next Twelve Months	0.4
Capital Leases, Future Minimum Payments Due in Two Years	0.4
Capital Leases, Future Minimum Payments Due in Three Years	0.4
Capital Leases, Future Minimum Payments Due in Four Years	0.4
Capital Leases, Future Minimum Payments Due in Five Years	0.4
Capital Leases, Future Minimum Payments Due Thereafter	4
Capital Leases, Future Minimum Payments Due, Total	6
Total Commitments [Abstract]
Total Commitments, Due in Next Twelve Months	504.4
Total Commitments, Due within Two Years	278.4
Total Commitments, Due within Three Years	231.4
Total Commitments, Due within Four Years	182.4
Total Commitments, Due within Five Years	206.9
Total Commitments, Due Thereafter	805.4
Total Commitments Due	2,208.90
Public Utilities, Inventory, Fuel [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	374.6
Unrecorded Unconditional Purchase Obligation, Due within Two Years	184.9
Unrecorded Unconditional Purchase Obligation, Due within Three Years	163
Unrecorded Unconditional Purchase Obligation, Due within Four Years	112.2
Unrecorded Unconditional Purchase Obligation, Due within Five Years	138.2
Unrecorded Unconditional Purchase Obligation, Due after Five Years	70.9
Unrecorded Unconditional Purchase Obligation, Total	1,043.80
Purchased Power [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	47.3
Unrecorded Unconditional Purchase Obligation, Due within Two Years	47.3
Unrecorded Unconditional Purchase Obligation, Due within Three Years	47.3
Unrecorded Unconditional Purchase Obligation, Due within Four Years	47.3
Unrecorded Unconditional Purchase Obligation, Due within Five Years	47.3
Unrecorded Unconditional Purchase Obligation, Due after Five Years	556.8
Unrecorded Unconditional Purchase Obligation, Total	793.3
Capacity [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	3
Unrecorded Unconditional Purchase Obligation, Due within Two Years	1.2
Unrecorded Unconditional Purchase Obligation, Due within Three Years	0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation, Total	4.2
Non-regulated natural gas transportation [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	3.5
Unrecorded Unconditional Purchase Obligation, Due within Two Years	3.5
Unrecorded Unconditional Purchase Obligation, Due within Three Years	1
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation, Total	8
La Cygne Environmental Project [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	16.6
Unrecorded Unconditional Purchase Obligation, Due within Two Years	0
Unrecorded Unconditional Purchase Obligation, Due within Three Years	0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation, Total	16.6
Other purchase commitments [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	44.8
Unrecorded Unconditional Purchase Obligation, Due within Two Years	31.1
Unrecorded Unconditional Purchase Obligation, Due within Three Years	10
Unrecorded Unconditional Purchase Obligation, Due within Four Years	12.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years	12
Unrecorded Unconditional Purchase Obligation, Due after Five Years	44.2
Unrecorded Unconditional Purchase Obligation, Total	154.9
Kansas City Power and Light Company [Member]
Lease Expense [Abstract]
Lease expense	14	16	17.7
Operating Leases [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	12.8
Operating Leases, Future Minimum Payments, Due in Two Years	9.9
Operating Leases, Future Minimum Payments, Due in Three Years	9.7
Operating Leases, Future Minimum Payments, Due in Four Years	9.7
Operating Leases, Future Minimum Payments, Due in Five Years	9
Operating Leases, Future Minimum Payments, Due Thereafter	129.5
Operating Leases, Future Minimum Payments Due, Total	180.6
Capital Leases [Abstract]
Capital Leases, Future Minimum Payments Due, Next Twelve Months	0.2
Capital Leases, Future Minimum Payments Due in Two Years	0.2
Capital Leases, Future Minimum Payments Due in Three Years	0.2
Capital Leases, Future Minimum Payments Due in Four Years	0.2
Capital Leases, Future Minimum Payments Due in Five Years	0.2
Capital Leases, Future Minimum Payments Due Thereafter	2
Capital Leases, Future Minimum Payments Due, Total	3
Total Commitments [Abstract]
Total Commitments, Due in Next Twelve Months	427.3
Total Commitments, Due within Two Years	214
Total Commitments, Due within Three Years	184.1
Total Commitments, Due within Four Years	137.6
Total Commitments, Due within Five Years	169
Total Commitments, Due Thereafter	633.2
Total Commitments Due	1,765.20
Reimbursement by Other Owners per Year (2015)	1.9
Reimbursements by Other Owners per Year (2016 to 2025)	0.4
Reimbursements by Other Owners Total	6.1
Kansas City Power and Light Company [Member] | Supply Commitment [Member]
Total Commitments [Abstract]
Capacity Sales Agreements per Year (2015 to 2016)	5.5
Capacity Sales Agreements per Year (2017 to 2018)	1.3
Capacity Sales Agreements per Year (2019)	0.9
Kansas City Power and Light Company [Member] | Public Utilities, Inventory, Fuel [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	318.8
Unrecorded Unconditional Purchase Obligation, Due within Two Years	138.2
Unrecorded Unconditional Purchase Obligation, Due within Three Years	130.8
Unrecorded Unconditional Purchase Obligation, Due within Four Years	81.5
Unrecorded Unconditional Purchase Obligation, Due within Five Years	114.4
Unrecorded Unconditional Purchase Obligation, Due after Five Years	70.9
Unrecorded Unconditional Purchase Obligation, Total	854.6
Kansas City Power and Light Company [Member] | Purchased Power [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	34.8
Unrecorded Unconditional Purchase Obligation, Due within Two Years	34.8
Unrecorded Unconditional Purchase Obligation, Due within Three Years	34.8
Unrecorded Unconditional Purchase Obligation, Due within Four Years	34.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years	34.8
Unrecorded Unconditional Purchase Obligation, Due after Five Years	394.6
Unrecorded Unconditional Purchase Obligation, Total	568.6
Kansas City Power and Light Company [Member] | Capacity [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	3
Unrecorded Unconditional Purchase Obligation, Due within Two Years	1.2
Unrecorded Unconditional Purchase Obligation, Due within Three Years	0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation, Total	4.2
Kansas City Power and Light Company [Member] | La Cygne Environmental Project [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	16.6
Unrecorded Unconditional Purchase Obligation, Due within Two Years	0
Unrecorded Unconditional Purchase Obligation, Due within Three Years	0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation, Total	16.6
Kansas City Power and Light Company [Member] | Other purchase commitments [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	41.1
Unrecorded Unconditional Purchase Obligation, Due within Two Years	29.7
Unrecorded Unconditional Purchase Obligation, Due within Three Years	8.6
Unrecorded Unconditional Purchase Obligation, Due within Four Years	11.4
Unrecorded Unconditional Purchase Obligation, Due within Five Years	10.6
Unrecorded Unconditional Purchase Obligation, Due after Five Years	36.2
Unrecorded Unconditional Purchase Obligation, Total	$137.60

Commitments_and_Contingencies_2

Commitments and Contingencies Environmental Matters (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
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
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)	22,000,000
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	225
LaCygne Station [Member]
Best Available Retrofit Technology Rule [Abstract]
Predetermination request for environmental equipment required at LaCygne Station to comply with BART	1,230
Entity's ownership percentage in facility (in hundredths)	50.00%
Kansas City Power and Light Company [Member]
Estimates Of Environmental Financial Impact And Related Issues [Line Items]
Current estimate of capital expenditures final regulations	700
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)	17,000,000
Minimum required renewable energy generation capacity percentage in Kansas	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	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]
Estimates Of Environmental Financial Impact And Related Issues [Line Items]
Cash capital expenditures incurred for La Cygne environmental project	500
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	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	1.4
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) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014
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
Unfavorable Regulatory Action [Member]
Loss Contingencies [Line Items]
Loss Contingency, Inestimable Loss	Due to the uncertainties remaining in the case, the potential refund or range of potential refunds owed by MPS Merchant are not reasonably estimable

Guarantees_Details

Guarantees (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$139.50
Guarantor Obligations, Origin and Purpose	In the ordinary course of business, Great Plains Energy and certain of its subsidiaries enter into various agreements providing financial or performance assurance to third parties on behalf of certain subsidiaries. Such agreements include, for example, guarantees and letters of credit. These agreements are entered into primarily to support or enhance the creditworthiness otherwise attributed to a subsidiary on a stand-alone basis, thereby facilitating the extension of sufficient credit to accomplish the subsidiary's intended business purposes.
Direct Guarantee [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	40.7
Guarantor Obligations, Term	expire in 2015 and 2016
Guarantor Obligations, Origin and Purpose	direct guarantees to GMO counterparties
Guarantee of Indebtedness of Others [Member] | Long-term Debt [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	98.8
Guarantor Obligations, Term	maturity dates ranging from 2015 to 2023
Guarantor Obligations, Origin and Purpose	guarantee of GMO long-term debt
Guarantee of Indebtedness of Others [Member] | Commercial Paper [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$0
Guarantor Obligations, Origin and Purpose	guaranteed GMO's commercial paper program

Related_Party_Transactions_and2

Related Party Transactions and Relationships (Details) (Kansas City Power and Light Company [Member], USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
KCPL Greater Missouri Operations [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$38.20	$32.70
KCPL employees manage GMO's business and operate its facilities at cost	173.9	223.6	207.9
KCPL net wholesale sales to GMO	12.7	25.6	29.4
KCPL Greater Missouri Operations [Member] | Money Pool [Member]
Related Party Transaction [Line Items]
Payable to Related Party	12.6	0.2
Great Plains Energy [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$18	$17.50

Derivative_Instruments_Details

Derivative Instruments (Details) (USD $)	Dec. 31, 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	$14.90	$19.30
Fair Value	-2.4	-0.6
Forward Contracts [Member] | Not Designated as Hedging Instrument [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	29.7	47.7
Fair Value	4.1	5.2
Option contracts [Member] | Not Designated as Hedging Instrument [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	1.7	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	28.3	22.9
Fair Value	2.6	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	0	7.7
Fair Value	0	-0.2
Kansas City Power and Light Company [Member] | Transmission Congestion Rights [Member] | Not Designated as Hedging Instrument [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	23.6	18
Fair Value	$3.10	$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 year one	32.00%
Percentage of expected on peak natural gas and natural gas equivalent purchased power price exposure hedged year two	15.00%
Percentage of expected on peak natural gas and natural gas equivalent purchased power price exposure hedged year three	9.00%

Derivative_Instruments_Cash_Fl

Derivative Instruments Cash Flow Hedge (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014
Derivative [Line Items]
Cash Flow Hedge Loss to be Reclassified within Twelve Months	$9.20
Kansas City Power and Light Company [Member]
Derivative [Line Items]
Cash Flow Hedge Loss to be Reclassified within Twelve Months	$8.80

Derivative_Instruments_Offsett

Derivative Instruments Offsetting Assets (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	$8.60	$8.50
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	-1.2	-0.7
Derivative Asset	7.4	7.8
Derivative, Collateral, Obligation to Return Securities	0	0
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	7.4	7.8
Kansas City Power and Light Company [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	4	1.2
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	-0.9	-0.1
Derivative Asset	3.1	1.1
Derivative, Collateral, Obligation to Return Securities	0	0
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	$3.10	$1.10

Derivative_Instruments_Offsett1

Derivative Instruments Offsetting Liabilities (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	$4.20	$1
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	-3.5	-0.9
Derivative Liability	0.7	0.1
Derivative, Collateral, Right to Reclaim Securities	0	0
Derivative, Collateral, Right to Reclaim Cash	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	0.7	0.1
Cash collateral posted with third parties as part of netting agreements	2.3	0.2
Kansas City Power and Light Company [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	0.9	0.3
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	-0.9	-0.3
Derivative Liability	0	0
Derivative, Collateral, Right to Reclaim Securities	0	0
Derivative, Collateral, Right to Reclaim Cash	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	$0	$0

Derivative_Instruments_Fair_Va

Derivative Instruments Fair Value (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$8.60	$8.50
Derivative Liability, Fair Value, Gross Liability	4.2	1
Kansas City Power and Light Company [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	4	1.2
Derivative Liability, Fair Value, Gross Liability	0.9	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	8.6	8.5
Derivative Liability, Fair Value, Gross Liability	4.2	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	4	1.2
Derivative Liability, Fair Value, Gross Liability	$0.90	$0.30

Derivative_Instruments_Gain_an

Derivative Instruments Gain and Losses (Details) (Not Designated as Hedging Instrument [Member], Commodity Contract [Member], USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
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	($20.30)	($0.90)	($10.30)
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	-2.7	0	-3.7
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	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	-13.3	0.8	0
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	-0.2	0	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	-4.9	0	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	1.5	-1.1	-6.6
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	1.1	0.8	0
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	-14.2	0	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	($14.20)	$0	$0

Fair_Value_Measurements_Level_

Fair Value Measurements Level 3 (Details) (Derivative Financial Instruments, Assets [Member], Fair Value, Inputs, Level 3 [Member], Fair Value, Measurements, Recurring [Member], USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net asset (liability) beginning of period	$3.30	$2.30
Purchases	16	1.7
Settlements	-11.2	-10.2
Net asset (liability) end of period	3.5	3.3
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	-4.9	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	14.6	9.5
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	-0.3	-0.3
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	-14.2	0
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	-0.2	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	-0.1	0
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	-0.1	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	1.1	0
Purchases	13.7	1.1
Settlements	2.7	0
Net asset (liability) end of period	3.1	1.1
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	-14.2	0
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	-0.2	0
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	-0.2	0
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	($0.20)	$0

Fair_Value_Measurements_Fair_V

Fair Value Measurements Fair Value Long-Term Debt (Details) (USD $)	Dec. 31, 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	3.8	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 $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Assets [Abstract]
Derivative instruments, assets	$8.60		$8.50
Liabilities [Abstract]
Derivative instruments, liabilities	4.2		1
Kansas City Power and Light Company [Member]
Assets [Abstract]
Derivative instruments, assets	4		1.2
Liabilities [Abstract]
Derivative instruments, liabilities	0.9		0.3
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Derivative instruments, assets	8.6	[1]	8.5	[1]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	199	[2]	183.9	[2]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	15.1	[3]	14.8	[3]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	17.9	[4]	18.7	[4]
Total assets	240.6		225.9
Liabilities [Abstract]
Derivative instruments, liabilities	4.2	[1]	1	[1]
Total liabilities	4.2		1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative instruments, assets	0	[1]	0.3	[1]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	162.3	[2]	152.7	[2]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	7.5	[3]	4.8	[3]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0.1	[4]	0.1	[4]
Total assets	169.9		157.9
Liabilities [Abstract]
Derivative instruments, liabilities	2.4	[1]	0.9	[1]
Total liabilities	2.4		0.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Derivative instruments, assets	3.4	[1]	4.9	[1]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	36.7	[2]	31.2	[2]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	7.6	[3]	10	[3]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	17.8	[4]	18.6	[4]
Total assets	65.5		64.7
Liabilities [Abstract]
Derivative instruments, liabilities	0.1	[1]	0.1	[1]
Total liabilities	0.1		0.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets	5.2	[1]	3.3	[1]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	[2]	0	[2]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	[3]	0	[3]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0	[4]	0	[4]
Total assets	5.2		3.3
Liabilities [Abstract]
Derivative instruments, liabilities	1.7	[1]	0	[1]
Total liabilities	1.7		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member]
Assets [Abstract]
Derivative instruments, assets	4	[1]	1.2	[1]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	199		183.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	15.1		14.8
SERP rabbi trust [Abstract]
Total assets	218.1		199.9
Liabilities [Abstract]
Derivative instruments, liabilities	0.9	[1]	0.3	[1]
Total liabilities	0.9		0.3
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	137.1		127.7
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	1.3		0.9
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	7.6		9.3
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	22.9		21.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	3.5		2.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	4.1		3.9
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	28.1		24.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [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] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	2.3		3.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Other Assets [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.5		-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] | Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	6.2		3.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative instruments, assets	0	[1]	0.1	[1]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	162.3		152.7
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	7.5		4.8
SERP rabbi trust [Abstract]
Total assets	169.8		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	137.1		127.7
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	1.3		0.9
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0		0.5
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	22.9		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	2.3		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	6.2		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	36.7		31.2
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	7.6		10
SERP rabbi trust [Abstract]
Total assets	44.3		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	7.6		8.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	3.5		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	4.1		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	28.1		24.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.5		0.5
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Other Assets [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.5		-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	4	[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	4		1.1
Liabilities [Abstract]
Derivative instruments, liabilities	0.9	[1]	0	[1]
Total liabilities	0.9		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]
Assets [Abstract]
Derivative instruments, assets	4.6	[1]	7.3	[1]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	17.9		18.7
Total assets	22.5		26
Liabilities [Abstract]
Derivative instruments, liabilities	3.3	[1]	0.7	[1]
Total liabilities	3.3		0.7
Fair Value, Measurements, Recurring [Member] | Other Great Plains [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] | Fixed Income Funds [Member]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	17.8		18.6
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative instruments, assets	0	[1]	0.2	[1]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0.1		0.1
Total assets	0.1		0.3
Liabilities [Abstract]
Derivative instruments, liabilities	2.4	[1]	0.6	[1]
Total liabilities	2.4		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	3.4	[1]	4.9	[1]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	17.8		18.6
Total assets	21.2		23.5
Liabilities [Abstract]
Derivative instruments, liabilities	0.1	[1]	0.1	[1]
Total liabilities	0.1		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	17.8		18.6
Fair Value, Measurements, Recurring [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets	1.2	[1]	2.2	[1]
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0		0
Total assets	1.2		2.2
Liabilities [Abstract]
Derivative instruments, liabilities	0.8	[1]	0	[1]
Total liabilities	0.8		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 for equity securities and NAV per share for fixed income funds. The fixed income fund invests primarily in intermediate and long-term debt securities, can be redeemed immediately and is not subject to any restrictions on redemptions.

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Income (Loss) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	($25.30)	[1]	($38.40)	[1]
Other comprehensive income before reclassifications	-1.8	[1]	1.2	[1]
Amounts reclassified from accumulated other comprehensive loss	8.4	[1]	11.9	[1]
Net current period other comprehensive income	6.6	[1]	13.1	[1]	11.4
Ending balance	-18.7	[1]	-25.3	[1]	-38.4	[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]
Other comprehensive income before reclassifications	0	[1]	0	[1]
Amounts reclassified from accumulated other comprehensive loss	8	[1]	11.6	[1]
Net current period other comprehensive income	8	[1]	11.6	[1]
Ending balance	-15.8	[1]	-23.8	[1]
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	-1.5	[1]	-3	[1]
Other comprehensive income before reclassifications	-1.8	[1]	1.2	[1]
Amounts reclassified from accumulated other comprehensive loss	0.4	[1]	0.3	[1]
Net current period other comprehensive income	-1.4	[1]	1.5	[1]
Ending balance	-2.9	[1]	-1.5	[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	5.3		5.6		5.6
Ending balance	-14.9		-20.2
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	5.3	[1]	5.6	[1]
Net current period other comprehensive income	5.3	[1]	5.6	[1]
Ending balance	($14.90)	[1]	($20.20)	[1]
[1]	Net of tax

Accumulated_Other_Comprehensiv3

Accumulated Other Comprehensive Income (Loss) Reclassification (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges									($188.50)	($198.40)	($220.80)
Fuel									-489.2	-539.5	-539.5
Utility operating and maintenance expenses									-701.9	-671.4	-647.3
Income before income tax (expense) benefit and income (loss) from equity investments									358.5	379.6	304.9
Income tax (expense) benefit									-115.7	-129.2	-104.6
Net income (loss)	19.5	147.4	52.1	23.8	17.5	143.1	63.6	26
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)									-8.4	-11.9
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									-13.1	-18.9
Income tax (expense) benefit									5.1	7.3
Net income (loss)									-8	-11.6
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									-13.1	-18.6
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	-0.3
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									-0.6	-0.5
Income before income tax (expense) benefit and income (loss) from equity investments									-0.6	-0.5
Income tax (expense) benefit									0.2	0.2
Net income (loss)									-0.4	-0.3
Kansas City Power and Light Company [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges									-124.1	-125.3	-127.6
Fuel									-364.9	-383	-384.8
Utility operating and maintenance expenses									-489.1	-475.9	-460.1
Income before income tax (expense) benefit and income (loss) from equity investments									238.1	248.8	216.9
Income tax (expense) benefit									-75.7	-79.8	-75.3
Net income (loss)	15.9	94.5	34.8	17.2	12.2	96.4	44.2	16.2
Kansas City Power and Light Company [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income tax (expense) benefit and income (loss) from equity investments									-8.7	-9.1
Income tax (expense) benefit									3.4	3.5
Net income (loss)									-5.3	-5.6
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									-8.7	-8.8
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] | Commodity Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Fuel									$0	($0.30)

Income_Tax_Expense_Details

Income Tax Expense (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current income taxes
Federal	$0.40	$0.30	($3.20)
State	-0.1	-3	-6.3
Current Income Tax Expense (Benefit), Total	0.3	-2.7	-9.5
Deferred income taxes
Federal	104.2	109.1	96.3
State	21.6	24.9	24.9
Deferred Income Tax Expense (Benefit), Total	125.8	134	121.2
Noncurrent income taxes
Federal	-2.4	0	-0.2
State	-0.5	-0.3	-0.3
Foreign	-6.1	-0.4	-4.2
Noncurrent Income Tax Expense (Benefit), Total	-9	-0.7	-4.7
Investment tax credit
Deferral	0	0.3	0
Investment tax credit amortization	-1.4	-1.7	-2.4
Investment Tax Credit, Total	-1.4	-1.4	-2.4
Total income tax expense	115.7	129.2	104.6
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax (in hundredths)	35.00%	35.00%	35.00%
Differences between book and tax depreciation not normalized (in hundredths)	-0.70%	-0.30%	1.20%
Amortization of investments tax credits (in hundredths)	-0.40%	-0.40%	-0.80%
Federal income tax credits (in hundredths)	-3.80%	-3.50%	-3.10%
State income taxes (in hundredths)	3.80%	3.80%	4.00%
Changes in uncertain tax positions, net (in hundredths)	-1.70%	-0.20%	-1.50%
Effective Income Tax Rate Reconciliation, Other Adjustments	0.10%	-0.40%	-0.50%
Effective Income Tax Rate Reconciliation, Percent	32.30%	34.00%	34.30%
Kansas City Power and Light Company [Member]
Current income taxes
Federal	-9.4	-0.5	13.1
State	-2.3	-0.5	2
Current Income Tax Expense (Benefit), Total	-11.7	-1	15.1
Deferred income taxes
Federal	72.6	75.8	48.8
State	15.8	16.3	11.4
Deferred Income Tax Expense (Benefit), Total	88.4	92.1	60.2
Noncurrent income taxes
Federal	0	-9	1.7
State	0	-1.5	0.1
Noncurrent Income Tax Expense (Benefit), Total	0	-10.5	1.8
Investment tax credit
Deferral	0	0.3	0
Investment tax credit amortization	-1	-1.1	-1.8
Investment Tax Credit, Total	-1	-0.8	-1.8
Total income tax expense	75.7	79.8	75.3
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax (in hundredths)	35.00%	35.00%	35.00%
Differences between book and tax depreciation not normalized (in hundredths)	-0.90%	-0.80%	1.30%
Amortization of investments tax credits (in hundredths)	-0.40%	-0.40%	-0.80%
Federal income tax credits (in hundredths)	-5.60%	-5.30%	-4.30%
State income taxes (in hundredths)	3.70%	3.70%	4.10%
Effective Income Tax Rate Reconciliation, Other Adjustments	0.00%	-0.10%	-0.60%
Effective Income Tax Rate Reconciliation, Percent	31.80%	32.10%	34.70%
Parent Company [Member]
Deferred income taxes
Deferred Income Tax Expense (Benefit), Total	-1.4	-10.5	-4.8
Investment tax credit
Total income tax expense	($4.40)	($4.20)	($11.60)

Taxes_Deferred_Income_Taxes_De

Taxes Deferred Income Taxes (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Deferred Tax Assets (Liabilities), Net of Valuation Allowance, Current Classification [Abstract]
Net operating loss carryforward, current	$62.20	$76.60
Deferred tax assets (liabilities), other current	17.1	5.7
Deferred tax assets (liabilities), before valuation allowance, current	79.3	82.3
Valuation allowance, current	-1.2	-2
Deferred Tax Assets (Liabilities), Net, Current	78.1	80.3
Deferred Tax Assets (Liabilities), Net of Valuation Allowance, Noncurrent Classification [Abstract]
Plant related	-1,648.20	-1,433.80
Income taxes on future regulatory recoveries	-133.4	-136.4
Derivative instruments	26.5	32.3
Pension and post-retirement benefits	-14	-28.2
SO2 emission allowance sales	27.1	28.8
Tax credit carryforwards	242.7	229.3
Customer demand programs	-26.2	-27.7
Solar rebates	-33.2	-17.5
Net operating loss carryforward, noncurrent	524.7	446.7
Deferred Tax Liabilities, Other	-40.3	-39.6
Deferred tax assets (liabilities), before valuation allowance, noncurrent	-1,074.30	-946.1
Valuation allowance, noncurrent	-15.4	-18.7
Deferred Tax Assets (Liabilities), Net, Noncurrent	-1,089.70	-964.8
Deferred Tax Assets (Liabilities), Net	-1,011.60	-884.5
Deferred Tax Assets (Liabilities), Gross [Abstract]
Deferred Tax Assets, Gross	1,227	1,148.20
Deferred Tax Liabilities, Gross	-2,238.60	-2,032.70
Deferred Tax Assets, Net	-1,011.60	-884.5
Kansas City Power and Light Company [Member]
Deferred Tax Assets (Liabilities), Net of Valuation Allowance, Current Classification [Abstract]
Net operating loss carryforward, current	0	0
Deferred tax assets (liabilities), other current	5	-1.7
Deferred tax assets (liabilities), before valuation allowance, current	5	-1.7
Valuation allowance, current	0	0
Deferred Tax Assets (Liabilities), Net, Current	5	-1.7
Deferred Tax Assets (Liabilities), Net of Valuation Allowance, Noncurrent Classification [Abstract]
Plant related	-1,167.30	-1,022.90
Income taxes on future regulatory recoveries	-107.1	-111
Derivative instruments	18.9	23.4
Pension and post-retirement benefits	12.5	-1.7
SO2 emission allowance sales	27.3	28.8
Tax credit carryforwards	153.2	139.6
Customer demand programs	-19	-19.4
Solar rebates	-11.3	-5.1
Net operating loss carryforward, noncurrent	98.5	71.6
Deferred Tax Liabilities, Other	-22.6	-25.4
Deferred tax assets (liabilities), before valuation allowance, noncurrent	-1,016.90	-922.1
Valuation allowance, noncurrent	0	0
Deferred Tax Assets (Liabilities), Net, Noncurrent	-1,016.90	-922.1
Deferred Tax Assets (Liabilities), Net	-1,011.90	-923.8
Deferred Tax Assets (Liabilities), Gross [Abstract]
Deferred Tax Assets, Gross	624.8	583
Deferred Tax Liabilities, Gross	-1,636.70	-1,506.80
Deferred Tax Assets, Net	($1,011.90)	($923.80)

Taxes_Net_Operating_Loss_Carry

Taxes Net Operating Loss Carryforwards (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	521	$459.90
Amount of Net Operating Losses related to business acquisition	313.2	304.6
Net operating losses year of origination [Abstract]
Net operating loss carryforwards originating in 2003	30.1
Net operating loss carryfowards originating in 2004	152.4
Net operating loss carryfowards originating in 2005	74.1
Net operating loss carryfowards originating in 2006	53.3
Net operating loss carryfowards originating in 2007	1.3
Net operating loss carryfowards originating in 2008	2.4
Net operating loss carryfowards originating in 2009	36.6
Net operating loss carryfowards originating in 2010	5
Net operating loss carryfowards originating in 2011	109.5
Net operating loss carryforwards originating in 2012	2.6
Net operating loss carryforwards originating in 2013	3.2
Net operating loss carryforwards originating in 2014	50.5
Internal Revenue Service (IRS) [Member] | Minimum [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	31-Dec-23
Internal Revenue Service (IRS) [Member] | Maximum [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	31-Dec-34
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	65.9	63.4
Amount of Net Operating Losses related to business acquisition	40.7	44.4
Operating Loss Carryforwards, Valuation Allowance	16.2

Taxes_Tax_Credit_Carryforwards

Taxes Tax Credit Carryforwards (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Tax Credit Carryforward [Line Items]
Valuation Allowance, Deferred Tax Asset, Explanation of Change	tax benefit was recorded in continuing operations primarily related to state NOL carryforwards offset by an increase in deferred tax expense since a portion of state NOLs expired at December 31, 2014 and 2013, respectively.	tax benefit was recorded in continuing operations primarily related to state NOL carryforwards offset by an increase in deferred tax expense since a portion of state NOLs expired at December 31, 2014 and 2013, respectively.
General Business Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	155.1	141.1
Amount of tax credit acquired in business combination	0.5
Tax Credit Carryforward, Description	relate primarily to Advanced Coal Investment Tax Credits and Wind Production tax credits	relate primarily to Advanced Coal Investment Tax Credits and Wind Production tax credits
Tax Credit Carryforward, Valuation Allowance	0.4
General Business Tax Credit Carryforward [Member] | Minimum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	31-Dec-28
General Business Tax Credit Carryforward [Member] | Maximum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	31-Dec-34
Federal Alternative Minimum Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	87.6	87.9
Amount of tax credit acquired in business combination	87.6	87.6
Tax Credit Carryforward, Description	These credits do not expire and can be used to reduce taxes paid in the future.	These credits do not expire and can be used to reduce taxes paid in the future.
State and Local Jurisdiction [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	0	0.3
Tax Credit Carryforward, Description		related primarily to the Company's Missouri affordable housing investment portfolio
Kansas City Power and Light Company [Member] | General Business Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	153.2	139.6
Tax Credit Carryforward, Description	relate primarily to Advanced Coal Investment Tax Credits and Wind Production tax credits	relate primarily to Advanced Coal Investment Tax Credits and Wind Production tax credits
Kansas City Power and Light Company [Member] | General Business Tax Credit Carryforward [Member] | Minimum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	31-Dec-28
Kansas City Power and Light Company [Member] | General Business Tax Credit Carryforward [Member] | Maximum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	31-Dec-34

Taxes_Valuation_Allowance_Deta

Taxes Valuation Allowance (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Valuation Allowance [Line Items]
Valuation Allowance, Deferred Tax Asset, Change in Amount	$4.10	$3.10
Valuation Allowance, Deferred Tax Asset, Explanation of Change	tax benefit was recorded in continuing operations primarily related to state NOL carryforwards offset by an increase in deferred tax expense since a portion of state NOLs expired at December 31, 2014 and 2013, respectively.	tax benefit was recorded in continuing operations primarily related to state NOL carryforwards offset by an increase in deferred tax expense since a portion of state NOLs expired at December 31, 2014 and 2013, respectively.

Taxes_Uncertain_Tax_Positions_

Taxes Uncertain Tax Positions (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Uncertain Tax Positions [Line Items]
Amount expected to impact the effective tax rate if recognized	$0.30	$6.50	$7.30
Unrecognized Tax Benefits, Period Decrease	7.2	11.6
Unrecognized tax benefit decrease related to former GMO non-regulated operations	6.1
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0	0.6	0.7
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	0	3.2	3.5
Interest expense related to unrecognized tax benefits	-3.2	-0.1	-2.3
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	9.8	21.4	24
Additions for current year tax positions	0	0	3.7
Reductions for current year tax positions	-0.3	-0.3	0
Reductions for prior year tax positions	-6.9	-10.5	-1.8
Statute expirations	0	-0.3	-4.7
Foreign currency translation adjustments	0	-0.5	0.2
Balance at end of period	2.6	9.8	21.4
Kansas City Power and Light Company [Member]
Uncertain Tax Positions [Line Items]
Amount expected to impact the effective tax rate if recognized			0
Unrecognized Tax Benefits, Period Decrease		10.5
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	0	10.5	8.7
Additions for current year tax positions	0	0	3.6
Reductions for current year tax positions	0	0	0
Reductions for prior year tax positions	0	-10.5	-1.6
Statute expirations	0	0	-0.2
Foreign currency translation adjustments	0	0	0
Balance at end of period	$0	$0	$10.50

Segments_and_Related_Informati2

Segments and Related Information (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating revenues	$552.20	$782.50	$648.40	$585.10	$538.80	$765	$600.30	$542.20	$2,568.20	$2,446.30	$2,309.90
Depreciation and amortization									-306	-289.7	-272.3
Interest charges									-188.5	-198.4	-220.8
Income tax (expense) benefit									-115.7	-129.2	-104.6
Net income (loss)									242.8	250.2	199.9
Assets, Total	10,475.70				9,795.40				10,475.70	9,795.40	9,647.30
Capital expenditures									773.7	669	610.2
Operating Segments [Member] | Electric Utility Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues									2,568.20	2,446.30	2,309.90
Depreciation and amortization									-306	-289.7	-272.3
Interest charges									-183	-190.5	-197.3
Income tax (expense) benefit									-125.6	-135.4	-122
Net income (loss)									243.5	257.1	216.6
Assets, Total	10,746.10				10,019.60				10,746.10	10,019.60	9,910.60
Capital expenditures									773.7	669	610.2
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues									0	0	0
Depreciation and amortization									0	0	0
Interest charges									-41.2	-55.5	-67.3
Income tax (expense) benefit									9.9	6.2	17.4
Net income (loss)									-0.7	-6.9	-16.7
Assets, Total	33.1				105.6				33.1	105.6	122.4
Capital expenditures									0	0	0
Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues									0	0	0
Depreciation and amortization									0	0	0
Interest charges									35.7	47.6	43.8
Income tax (expense) benefit									0	0	0
Net income (loss)									0	0	0
Assets, Total	-303.5				-329.8				-303.5	-329.8	-385.7
Capital expenditures									$0	$0	$0

Jointly_Owned_Electric_Utility2

Jointly Owned Electric Utility Plants (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Jointly Owned Utility Plant Interests [Line Items]
Nuclear fuel, net	$79.20	$62.80
Jeffrey Energy Center [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	8.00%
Utility plant in service	172.7
Accumulated depreciation	77.3
Nuclear fuel, net	0
Construction work in progress	19.9
Accredited capacity (in MW's)	172
Iatan Common [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	79.00%
Utility plant in service	441.2
Accumulated depreciation	99
Nuclear fuel, net	0
Construction work in progress	18.6
Iatan No. 2 [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	73.00%
Utility plant in service	1,318.30
Accumulated depreciation	342
Nuclear fuel, net	0
Construction work in progress	16.6
Accredited capacity (in MW's)	641
Iatan No. 1 [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	88.00%
Utility plant in service	645.8
Accumulated depreciation	261.8
Nuclear fuel, net	0
Construction work in progress	19.3
Accredited capacity (in MW's)	627
LaCygne Station [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	50.00%
Utility plant in service	562.6
Accumulated depreciation	320.4
Nuclear fuel, net	0
Construction work in progress	533.9
Accredited capacity (in MW's)	696
Wolf Creek [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	47.00%
Utility plant in service	1,745.60
Accumulated depreciation	832.4
Nuclear fuel, net	79.2
Construction work in progress	74.6
Accredited capacity (in MW's)	549
Kansas City Power and Light Company [Member]
Jointly Owned Utility Plant Interests [Line Items]
Nuclear fuel, net	79.2	62.8
Kansas City Power and Light Company [Member] | Iatan Common [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	61.00%
Utility plant in service	357.8
Accumulated depreciation	89.2
Nuclear fuel, net	0
Construction work in progress	2.4
Kansas City Power and Light Company [Member] | Iatan No. 2 [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	55.00%
Utility plant in service	1,006.80
Accumulated depreciation	313.9
Nuclear fuel, net	0
Construction work in progress	7.8
Accredited capacity (in MW's)	482
Kansas City Power and Light Company [Member] | Iatan No. 1 [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	70.00%
Utility plant in service	515.4
Accumulated depreciation	211.4
Nuclear fuel, net	0
Construction work in progress	5.4
Accredited capacity (in MW's)	499
Kansas City Power and Light Company [Member] | LaCygne Station [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	50.00%
Utility plant in service	562.6
Accumulated depreciation	320.4
Nuclear fuel, net	0
Construction work in progress	533.9
Accredited capacity (in MW's)	696
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%
Utility plant in service	1,745.60
Accumulated depreciation	832.4
Nuclear fuel, net	79.2
Construction work in progress	$74.60
Accredited capacity (in MW's)	549

Quarterly_Operating_Results_Un2

Quarterly Operating Results (Unaudited) (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating revenues	$552.20	$782.50	$648.40	$585.10	$538.80	$765	$600.30	$542.20	$2,568.20	$2,446.30	$2,309.90
Operating income (loss)	69.2	263.2	124.2	77.9	67.8	271.7	143.6	86.1	534.5	569.2	538.9
Net income (loss)	19.5	147.4	52.1	23.8	17.5	143.1	63.6	26
Earnings Per Share, Basic	$0.12	$0.96	$0.34	$0.15					$1.57	$1.62	$1.36
Earnings Per Share, Diluted	$0.12	$0.95	$0.34	$0.15					$1.57	$1.62	$1.35
Earnings Per Share, Basic and Diluted					$0.11	$0.93	$0.41	$0.17
Kansas City Power and Light Company [Member]
Operating revenues	366.9	533.4	439.5	391	371.9	522	410.8	366.7	1,730.80	1,671.40	1,579.90
Operating income (loss)	47.2	177.2	78.2	47.5	40	176.8	93.4	52.3	350.1	362.5	348.7
Net income (loss)	$15.90	$94.50	$34.80	$17.20	$12.20	$96.40	$44.20	$16.20

Schedule_I_Financial_Statement1

Schedule I Financial Statements of Parent Company Statements of Income & OCI (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Operating Expenses
General and administrative									$4		$3		$7.50
General taxes									204.6		194.4		179.3
Operating Income (Loss)	69.2	263.2	124.2	77.9	67.8	271.7	143.6	86.1	534.5		569.2		538.9
Equity in earnings (loss) from Subsidiaries									0		-0.2		-0.4
Interest charges									-188.5		-198.4		-220.8
Income before income tax (expense) benefit and income (loss) from equity investments									358.5		379.6		304.9
Income tax (expense) benefit									-115.7		-129.2		-104.6
Net income (loss)	19.5	147.4	52.1	23.8	17.5	143.1	63.6	26
Preferred stock dividend requirements									1.6		1.6		1.6
Earnings (loss) available for common shareholders									241.2		248.6		198.3
Weighted Average Number of Shares Outstanding, Basic									153.9		153.5		145.5
Weighted Average Number of Shares Outstanding, Diluted									154.1		153.7		147.2
Earnings Per Share, Basic	$0.12	$0.96	$0.34	$0.15					$1.57		$1.62		$1.36
Earnings Per Share, Diluted	$0.12	$0.95	$0.34	$0.15					$1.57		$1.62		$1.35
Common Stock, Dividends, Per Share, Declared									$0.94		$0.88		$0.86
Comprehensive Income
Net income (loss)	19.5	147.4	52.1	23.8	17.5	143.1	63.6	26
Other comprehensive income
Gain (loss) on derivative hedging instruments									0		0		-0.1
Reclassification to expenses, net of tax									8		11.6		12.6
Derivative hedging activity, net of tax									8		11.6		12.5
Total other comprehensive income (loss)									6.6	[1]	13.1	[1]	11.4
Comprehensive income (loss)									249.4		263.3		211.3
Parent Company [Member]
Operating Expenses
General and administrative									1.1		1		3.3
General taxes									0.4		0.6		0.7
Operating Expenses									1.5		1.6		4
Operating Income (Loss)									-1.5		-1.6		-4
Equity in earnings (loss) from Subsidiaries									251.1		256.5		219.2
Non-operating income									33.1		45.8		42.7
Interest charges									-44.3		-54.7		-69.6
Income before income tax (expense) benefit and income (loss) from equity investments									238.4		246		188.3
Income tax (expense) benefit									4.4		4.2		11.6
Net income (loss)									242.8		250.2		199.9
Preferred stock dividend requirements									1.6		1.6		1.6
Earnings (loss) available for common shareholders									241.2		248.6		198.3
Weighted Average Number of Shares Outstanding, Basic									153.9		153.5		145.5
Weighted Average Number of Shares Outstanding, Diluted									154.1		153.7		147.2
Earnings Per Share, Basic									$1.57		$1.62		$1.36
Earnings Per Share, Diluted									$1.57		$1.62		$1.35
Comprehensive Income
Net income (loss)									242.8		250.2		199.9
Other comprehensive income
Reclassification to expenses									4.4		9.9		11.5
Income tax (expense) benefit on reclassification to expenses									-1.7		-3.9		-4.6
Reclassification to expenses, net of tax									2.7		6		6.9
Derivative hedging activity, net of tax									2.7		6		6.9
Other comprehensive income from subsidiaries, net of tax									3.9		7.1		4.5
Total other comprehensive income (loss)									6.6		13.1		11.4
Comprehensive income (loss)									$249.40		$263.30		$211.30
[1]	Net of tax

Schedule_I_Financial_Statement2

Schedule I Financial Statements of Parent Company Balance Sheet (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Current Assets
Taxes receivable	$3.10		$10.50
Assets, Current, Total	718.9		767
Investments and Other Assets
Deferred income taxes	-1,089.70		-964.8
Other Assets, Noncurrent	74.6		79.4
Assets, Total	10,475.70		9,795.40		9,647.30
Current Liabilities
Notes payable	4		9
Current maturities of long-term debt	15.1		1.1
Accrued taxes	30.4		29.7
Accrued interest	41.3		45.4
Other Liabilities, Current	24.7		23.5
Liabilities, Current, Total	1,070.80		769.8
Deferred Credits and Other Liabilities
Liabilities, Noncurrent, Total	2,291.80		1,996.50
Capitalization
Common Stock, Value, Issued	2,639.30		2,631.10
Retained earnings	967.8		871.4
Treasury Stock, Value	-2.3		-2.8
Accumulated Other Comprehensive Income (Loss), Net of Tax	-18.7	[1]	-25.3	[1]	-38.4	[1]
Common Shareholders' Equity, Total	3,586.10		3,474.40		3,340
Preferred Stock, Value, Issued	39		39
Long-term debt	3,488		3,515.70
Total Capitalization	7,113.10		7,029.10
Commitments and Contingencies
Liabilities and Equity, Total	10,475.70		9,795.40
Parent Company [Member]
Current Assets
Accounts receivable from subsidiaries	4		0.2
Notes receivable from subsidiaries, current	0.6		0.6
Money pool receivable	3.3		9.4
Taxes receivable	0		0.2
Other current assets	1		1.2
Assets, Current, Total	8.9		11.6
Investments and Other Assets
Investment in KCP&L	2,275		2,179.30
Investment in other subsidiaries	1,465.90		1,447
Notes receivable from subsidiaries, noncurrent	634.9		634.9
Deferred income taxes	32.8		31.4
Other Assets, Noncurrent	5.8		6.7
Total investments and other assets	4,414.40		4,299.30
Assets, Total	4,423.30		4,310.90
Current Liabilities
Notes payable	4		9
Accounts payable to subsidiaries	30.4		33.6
Accrued taxes	4.3		0.2
Accrued interest	4.1		4.2
Other Liabilities, Current	2.2		1.5
Liabilities, Current, Total	45		48.5
Deferred Credits and Other Liabilities
Liabilities, Noncurrent, Total	11.4		6.6
Capitalization
Common Stock, Value, Issued	2,639.30		2,631.10
Retained earnings	967.8		871.4
Treasury Stock, Value	-2.3		-2.8
Accumulated Other Comprehensive Income (Loss), Net of Tax	-18.7		-25.3
Common Shareholders' Equity, Total	3,586.10		3,474.40
Preferred Stock, Value, Issued	39		39
Long-term debt	741.8		742.4
Total Capitalization	4,366.90		4,255.80
Commitments and Contingencies
Liabilities and Equity, Total	4,423.30		4,310.90
Preferred Stock 3 Point 80 [Member]
Capitalization
Preferred Stock, Value, Issued	10		10
Preferred Stock 3 Point 80 [Member] | Parent Company [Member]
Capitalization
Preferred Stock, Value, Issued	10		10
Preferred Stock 4 Point 50 [Member]
Capitalization
Preferred Stock, Value, Issued	10		10
Preferred Stock 4 Point 50 [Member] | Parent Company [Member]
Capitalization
Preferred Stock, Value, Issued	10		10
Preferred Stock 4 Point 20 [Member]
Capitalization
Preferred Stock, Value, Issued	7		7
Preferred Stock 4 Point 20 [Member] | Parent Company [Member]
Capitalization
Preferred Stock, Value, Issued	7		7
Preferred Stock 4 Point 35 [Member]
Capitalization
Preferred Stock, Value, Issued	12		12
Preferred Stock 4 Point 35 [Member] | Parent Company [Member]
Capitalization
Preferred Stock, Value, Issued	$12		$12
[1]	Net of tax

Schedule_I_Financial_Statement3

Schedule I Financial Statements of Parent Company Balance Sheet Parenthetical (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Common Stock, Shares Authorized	250,000,000	250,000,000
Common Stock, Shares, Issued	154,254,037	153,995,621
Treasury Stock, Shares	91,281	129,290
Parent Company [Member]
Common Stock, Shares Authorized	250,000,000	250,000,000
Common Stock, Shares, Issued	154,254,037	153,995,621
Treasury Stock, Shares	91,281	129,290
Preferred Stock 3 Point 80 [Member]
Preferred Stock, Par or Stated Value Per Share	$100	$100
Preferred Stock, Dividend Rate, Percentage	3.80%	3.80%
Preferred Stock, Shares Issued	100,000	100,000
Preferred Stock 3 Point 80 [Member] | Parent Company [Member]
Preferred Stock, Par or Stated Value Per Share	$100	$100
Preferred Stock, Dividend Rate, Percentage	3.80%	3.80%
Preferred Stock, Shares Issued	100,000	100,000
Preferred Stock 4 Point 50 [Member]
Preferred Stock, Par or Stated Value Per Share	$100	$100
Preferred Stock, Dividend Rate, Percentage	4.50%	4.50%
Preferred Stock, Shares Issued	100,000	100,000
Preferred Stock 4 Point 50 [Member] | Parent Company [Member]
Preferred Stock, Par or Stated Value Per Share	$100	$100
Preferred Stock, Dividend Rate, Percentage	4.50%	4.50%
Preferred Stock, Shares Issued	100,000	100,000
Preferred Stock 4 Point 20 [Member]
Preferred Stock, Par or Stated Value Per Share	$100	$100
Preferred Stock, Dividend Rate, Percentage	4.20%	4.20%
Preferred Stock, Shares Issued	70,000	70,000
Preferred Stock 4 Point 20 [Member] | Parent Company [Member]
Preferred Stock, Par or Stated Value Per Share	$100	$100
Preferred Stock, Dividend Rate, Percentage	4.20%	4.20%
Preferred Stock, Shares Issued	70,000	70,000
Preferred Stock 4 Point 35 [Member]
Preferred Stock, Par or Stated Value Per Share	$100	$100
Preferred Stock, Dividend Rate, Percentage	4.35%	4.35%
Preferred Stock, Shares Issued	120,000	120,000
Preferred Stock 4 Point 35 [Member] | Parent Company [Member]
Preferred Stock, Par or Stated Value Per Share	$100	$100
Preferred Stock, Dividend Rate, Percentage	4.35%	4.35%
Preferred Stock, Shares Issued	120,000	120,000

Schedule_I_Financial_Statement4

Schedule I Financial Statements of Parent Company Statement of Cash Flows (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Adjustments to reconcile income to net cash from operating activities:
Deferred income taxes, net	$125.80	$134	$121.20
Equity in earnings from subsidiaries	0	0.2	0.4
Cash flows affected by changes in:
Accrued taxes	8.3	2.2	-7.8
Accrued interest	-4.1	3.9	-35.2
Uncertain tax positions	-9	-0.8	-4.7
Other operating activities	-3.3	17	-13.9
Net cash from operating activities	698.2	776.8	663.8
Cash Flows from Investing Activities
Other investing activities	-27.5	-21.7	-19.6
Net cash from investing activities	-779.8	-705.8	-638.4
Cash Flows from Financing Activities
Issuance of common stock	4.8	4.9	293
Issuance of long-term debt	0	762.5	0
Issuance fees	-0.9	-9	-2.9
Repayment of long-term debt	-13.4	-265.3	-513.8
Net change in short-term borrowings	245.1	-424.9	253.1
Dividends paid	-145.6	-137.3	-125.5
Other financing activities	-2	-1.6	-5.2
Net cash from financing activities	84	-69.7	-22.3
Net Change in Cash and Cash Equivalents	2.4	1.3	3.1
Cash and Cash Equivalents at Beginning of Year	10.6	9.3	6.2
Cash and Cash Equivalents at End of Year	13	10.6	9.3
Parent Company [Member]
Cash Flows from Operating Activities
Net income (loss)	242.8	250.2	199.9
Adjustments to reconcile income to net cash from operating activities:
Amortization	4.8	10.6	12.6
Deferred income taxes, net	-1.4	-10.5	-4.8
Equity in earnings from subsidiaries	-251.1	-256.5	-219.2
Cash flows affected by changes in:
Accounts receivable from subsidiaries	-3.8	-0.1	-0.1
Taxes receivable	0.2	-0.2	0.9
Accounts payable to subsidiaries	-3.2	-0.5	2.3
Other accounts payable	0	0.1	0
Accrued taxes	4.3	-0.1	-4.4
Accrued interest	-0.1	-2.6	6.1
Cash dividends from subsidiaries	144	140	144
Uncertain tax positions	-2.9	7.3	1
Other operating activities	11.8	6.8	1.7
Net cash from operating activities	145.4	144.5	140
Cash Flows from Investing Activities
Intercompany lending	0	248.7	-287.4
Net money pool lending	6.1	-5.4	-3.1
Investment in subsidiary	-3.6	-0.5	0
Net cash from investing activities	2.5	242.8	-290.5
Cash Flows from Financing Activities
Issuance of common stock	4.8	4.9	293
Issuance fees	-0.1	-0.4	-2.7
Repayment of long-term debt	0	-250	0
Net change in short-term borrowings	-5	-3	-10
Dividends paid	-145.6	-137.3	-125.5
Other financing activities	-2	-1.5	-4.3
Net cash from financing activities	-147.9	-387.3	150.5
Net Change in Cash and Cash Equivalents	0	0	0
Cash and Cash Equivalents at Beginning of Year	0	0	0
Cash and Cash Equivalents at End of Year	$0	$0	$0

Schedule_II_Valuation_and_Qual1

Schedule II Valuation and Qualifying Accounts (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$2.50		$6.90		$6.80
Additions charged to costs and expenses	11.4		12.3		12
Additions charged to other accounts	8.5	[1]	7.6	[1]	7.8	[1]
Deductions	19.6	[2]	24.3	[2]	19.7	[2]
Balance at end of period	2.8		2.5		6.9
Allowance for Doubtful Accounts [Member] | Kansas City Power and Light Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	1.1		1.5		1.4
Additions charged to costs and expenses	7.6		8		7.9
Additions charged to other accounts	5.5	[1]	5	[1]	5.2	[1]
Deductions	13	[2]	13.4	[2]	13	[2]
Balance at end of period	1.2		1.1		1.5
Legal Reserve [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	4.6		4.6		6.7
Additions charged to costs and expenses	2.7		2.7		-0.2
Additions charged to other accounts	0		0		0
Deductions	2.6	[3]	2.7	[3]	1.9	[3]
Balance at end of period	4.7		4.6		4.6
Legal Reserve [Member] | Kansas City Power and Light Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	2.9		2.9		3.9
Additions charged to costs and expenses	2.3		0.9		0.5
Additions charged to other accounts	0		0		0
Deductions	2.3	[3]	0.9	[3]	1.5	[3]
Balance at end of period	2.9		2.9		2.9
Reserve for Environmental Costs [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	1.7		2.3		2.5
Additions charged to costs and expenses	0		0		0
Additions charged to other accounts	0		0		0
Deductions	0		0.6		0.2
Balance at end of period	1.7		1.7		2.3
Reserve for Environmental Costs [Member] | Kansas City Power and Light Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	0.3		0.3		0.3
Additions charged to costs and expenses	0		0		0
Additions charged to other accounts	0		0		0
Deductions	0		0		0
Balance at end of period	0.3		0.3		0.3
Valuation Allowance of Deferred Tax Assets [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	20.7		23.8		23.9
Additions charged to costs and expenses	0.5		0.1		0.3
Additions charged to other accounts	0		0		0
Deductions	4.6	[4]	3.2	[4]	0.4	[4]
Balance at end of period	$16.60		$20.70		$23.80
[1]	Recoveries.
[2]	Uncollectible accounts charged off.
[3]	Payment of claims.
[4]	Reversal of tax valuation allowance.