SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $)	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Income [Abstract]
Income from continuing operations	$ 126,600,000	$ 132,000,000	$ 172,300,000	$ 216,700,000
Less: Net income attributable to noncontrolling interest	100,000	0	0	100,000
Less: preferred stock dividend requirements	400,000	400,000	1,200,000	1,200,000
Income from continuing operations available for common shareholders	126,100,000	131,600,000	171,100,000	215,400,000
Common Shares Outstanding [Abstract]
Average number of common shares outstanding	135,700,000	135,200,000	135,600,000	135,100,000
Add: effect of dilutive securities	2,600,000	1,700,000	2,900,000	1,700,000
Diluted average number of common shares outstanding	138,300,000	136,900,000	138,500,000	136,800,000
Basic EPS from continuing operations	$ 0.93	$ 0.97	$ 1.26	$ 1.59
Diluted EPS from continuing operations	$ 0.91	$ 0.96	$ 1.24	$ 1.57
Performance shares [Member]
Great Plains Energy anti-dilutive shares [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	102,032	107,958	102,032	116,388
Restricted Stock [Member]
Great Plains Energy anti-dilutive shares [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	22,818	103,114	45,648	278,452
Stock options [Member]
Great Plains Energy anti-dilutive shares [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	80,140	203,879	80,140	209,837
Great Plains Energy Incorporated [Member]
Dividends Declared [Line Iems]
Subsequent Event Date	Nov. 01, 2011		Nov. 01, 2011
Subsequent Event Description			Great Plains Energys Board of Directors declared a quarterly dividend and also declared regular dividends on Great Plains Energys preferred stock.
Subsequent Event Amount			0.2125
Kansas City Power and Light Company [Member]
Dividends Declared [Line Iems]
Subsequent Event Date	Nov. 01, 2011		Nov. 01, 2011
Subsequent Event Description			KCP&Ls Board of Directors declared a cash dividend payable to Great Plains Energy
Subsequent Event Amount			$ 25,000,000

Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) in the future that were not included in the computation of diluted EPS because to do so would increase EPS amounts or decrease loss per share amounts for the period presented.

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This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses and taxes from ongoing operations before extraordinary items, cumulative effects of changes in accounting principles, and noncontrolling interest.

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The amount of income (loss) from continuing operations per each share of common stock outstanding during the reporting period.

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The amount of income (loss) from continuing operations available to each share of common stock outstanding during the reporting period and each share that would have been outstanding assuming the issuance of common shares for all dilutive potential common shares outstanding during the reporting period.

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Aggregate awards of share options and nonvested shares to be issued to an employee under a share-based compensation arrangement are considered options for purposes of computing diluted earnings per share. Such share-based awards shall be considered to be outstanding as of the grant date for purposes of computing diluted earnings per share even though their exercise may be contingent upon vesting. Those share-based awards are included in the diluted Earnings Per Share (EPS) computation even if the employee may not receive (or be able to sell) the stock until some future date. Accordingly, all shares to be issued shall be included in computing diluted EPS if the effect is dilutive. The dilutive effect of share-based compensation arrangements shall be computed using the treasury stock method. If the equity share options or other equity instruments are outstanding for only part of a period, the shares issuable shall be weighted to reflect the portion of the period during which the equity instruments were outstanding.

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Amount of net income (loss) for the period allocated to noncontrolling shareholders, partners, or other equity holders in one or more of the entities consolidated into the reporting entity's financial statements other than joint ventures, limited partnerships, operating partnerships or interests held by preferred unit holders.

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The amount of dividends declared or paid in the period to preferred shareholders, or the amount for which the obligation to pay them dividends arose in the period.

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The average number of shares issued and outstanding that are used in calculating diluted EPS, determined based on the timing of issuance of shares in the period.

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Number of [basic] shares, after adjustment for contingently issuable shares and other shares not deemed outstanding, determined by relating the portion of time within a reporting period that common shares have been outstanding to the total time in that period.

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