Schedule I Financial Statements of Parent Company (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Jan. 02, 2010	Dec. 31, 2009	Dec. 31, 2008
Operating Expenses
Selling, general and administrative									$ 5.9	$ 22.1	$ 14.4
Maintenance									0	0	0.2
General taxes									170.9	155.1	139.8
Total									1,838.2	1,783.2	1,644.9
Operating loss	60.3	262.7	115.6	41.2	31.6	243.8	134.9	62.0	479.8	472.3	320.1
Equity in earnings from subsidiaries									200.8	239.3	174.7
Non-operating income									5.9	43.9	49.5
Interest charges									(218.4)	(184.8)	(180.9)
Income from continuing operations before income tax									259.1	311.9	181.8
Income tax (expense) benefit									(84.8)	(99.0)	(29.5)
Income from continuing operations									174.2	211.9	151.9
Equity in earnings (loss) from discontinued subsidiary									0	0	(1.5)
Net income (loss) attributable to Great Plains Energy	2.1	126.5	43.4	2.4	(4.9)	132.0	64.3	20.3	174.4	211.7	150.1
Preferred stock dividend requirements									1.6	1.6	1.6
Earnings available for common shareholders									172.8	210.1	148.5
Average number of basic common shares outstanding									135.6	135.1	129.3
Average number of diluted common shares outstanding									138.7	136.9	129.8
Basic earnings (loss) per common share
Continuing operations									$ 1.27	$ 1.55	$ 1.16
Discontinued operations									$ 0.00	$ 0.00	$ (0.01)
Basic earnings per common share	$ 0.01	$ 0.93	$ 0.32	$ 0.02	$ (0.04)	$ 0.97	$ 0.47	$ 0.15	$ 1.27	$ 1.55	$ 1.15
Diluted earnings (loss) per common share
Continuing operations									$ 1.25	$ 1.53	$ 1.15
Discontinued operations									$ 0.00	$ 0.00	$ (0.01)
Diluted earnings per common share	$ 0.01	$ 0.91	$ 0.31	$ 0.01	$ (0.04)	$ 0.96	$ 0.47	$ 0.15	$ 1.25	$ 1.53	$ 1.14
Cash dividends per common share									$ 0.835	$ 0.83	$ 0.83
Current Assets
Cash and cash equivalents	6.2				10.8				6.2	10.8			61.1
Taxes receivable	0.3				2.1				0.3	2.1
Total	619.1				611.6				619.1	611.6
Investments and Other Assets
Other	76.1				84.3				76.1	84.3
Total	1,445.4				1,314.3				1,445.4	1,314.3
Total	9,118.0				8,818.2				9,118.0	8,818.2		8,482.8
Current Liabilities
Current maturities of long-term debt	801.4				485.7				801.4	485.7
Accounts payable	275.6				276.3				275.6	276.3
Accrued taxes	25.8				26.6				25.8	26.6
Accrued interest	76.9				75.4				76.9	75.4
Derivative instruments	0				20.8				0	20.8
Other	26.0				35.6				26.0	35.6
Total	1,634.9				1,339.3				1,634.9	1,339.3
Deferred Credits and Other Liabilities
Other	101.1				129.4				101.1	129.4
Total	1,740.9				1,610.1				1,740.9	1,610.1
Common shareholders' equity
Common stock-250,000,000 shares authorized without par value 136,113,954 and 135,636,538 shares issued, stated value	2,330.6				2,324.4				2,330.6	2,324.4
Retained earnings	684.7				626.5				684.7	626.5
Treasury stock-264,567 and 400,889 shares, at cost	(5.6)				(8.9)				(5.6)	(8.9)
Accumulated other comprehensive loss	(49.8)				(56.1)				(49.8)	(56.1)
Total	2,959.9				2,885.9				2,959.9	2,885.9		2,792.5
Cumulative preferred stock $100 par value
3.8% - 100,000 shares issued	10.0				10.0				10.0	10.0
4.50% - 100,000 shares issued	10.0				10.0				10.0	10.0
4.20% - 70,000 shares issued	7.0				7.0				7.0	7.0
4.35% - 120,000 shares issued	12.0				12.0				12.0	12.0
Total	39.0				39.0				39.0	39.0
Long-term debt	2,742.3				2,942.7				2,742.3	2,942.7
Total	5,742.2				5,868.8				5,742.2	5,868.8
Commitments and Contingencies
Total	9,118.0				8,818.2				9,118.0	8,818.2
Cash Flows from Operating Activities
Net income	1.9	126.6	43.4	2.3	(4.8)	132.0	64.4	20.3	174.2	211.9	150.4
Adjustments to reconcile income to net cash from operating activities:
Amortization									11.2	3.9	1.9
Deferred income taxes, net									111.2	123.8	(3.6)
Equity in earnings from subsidiaries									(200.8)	(239.3)	(174.7)
Equity in (earnings) loss from discontinued subsidiary									0	0	1.5
Cash flows affected by changes in:
Accounts receivable from subsidiaries									0	(2.6)	3.7
Taxes receivable									6.3	0	4.8
Accounts payable to subsidiaries									(0.3)	2.2	0.2
Other accounts payable									0	(0.1)	0.1
Accrued taxes									1.4	6.7	42.2
Accrued interest									1.5	2.9	2.9
Cash dividends from subsidiaries									148.0	138.6	94.0
Other									(27.1)	(28.3)	9.0
Net cash from operating activities									443.0	552.1	335.4
Cash Flows from Investing Activities
Equity contributions to subsidiaries									0	0	(455.0)
Intercompany lending									(347.4)	(248.8)	0
Net cash from investing activities									(485.7)	(657.7)	(897.6)
Cash Flows from Financing Activities
Issuance of common stock									5.9	6.2	219.9
Issuance of long-term debt									747.1	249.9	700.7
Issuance fees									10.7	12.1	22.8
Net change in short-term borrowings									16.0	(165.6)	(145.6)
Dividends paid									115.1	114.2	110.5
Other financing activities									(6.6)	(7.4)	(4.0)
Net cash from financing activities									38.1	50.5	567.0
Net Change in Cash and Cash Equivalents									(4.6)	(55.1)	4.8
Cash and Cash Equivalents at Beginning of Year				10.8				65.9		65.9			61.1
Cash and Cash Equivalents at End of Year	6.2				10.8				6.2	10.8			61.1
Parent Company [Member]
Operating Expenses
Selling, general and administrative									0.8	1.2	8.8
Maintenance									0	0	0.2
General taxes									0.9	0.9	1.1
Total									1.7	2.1	10.1
Operating loss									(1.7)	(2.1)	(10.1)
Equity in earnings from subsidiaries									200.8	239.3	174.7
Non-operating income									24.7	3.4	0
Interest charges									(66.5)	(44.7)	(28.2)
Income from continuing operations before income tax									157.3	195.9	136.4
Income tax (expense) benefit									17.1	15.8	15.2
Income from continuing operations									174.4	211.7	151.6
Equity in earnings (loss) from discontinued subsidiary									0	0	(1.5)
Net income (loss) attributable to Great Plains Energy									174.4	211.7	150.1
Preferred stock dividend requirements									1.6	1.6	1.6
Earnings available for common shareholders									172.8	210.1	148.5
Average number of basic common shares outstanding									135.6	135.1	129.3
Average number of diluted common shares outstanding									138.7	136.9	129.8
Basic earnings (loss) per common share
Continuing operations									$ 1.27	$ 1.55	$ 1.16
Discontinued operations									$ 0.00	$ 0.00	$ (0.01)
Basic earnings per common share									$ 1.27	$ 1.55	$ 1.15
Diluted earnings (loss) per common share
Continuing operations									$ 1.25	$ 1.53	$ 1.15
Discontinued operations									$ 0.00	$ 0.00	$ (0.01)
Diluted earnings per common share									$ 1.25	$ 1.53	$ 1.14
Cash dividends per common share									$ 0.835	$ 0.83	$ 0.83
Current Assets
Cash and cash equivalents	0				0.3				0	0.3			12.0
Notes receivable from subsidiaries	0.6				249.4				0.6	249.4
Money pool receivable	0.9				2.0				0.9	2.0
Taxes receivable	0.9				7.2				0.9	7.2
Other	0.6				0.7				0.6	0.7
Total	3.0				259.6				3.0	259.6
Investments and Other Assets
Investment in KCP and L	2,045.5				2,005.0				2,045.5	2,005.0
Investments in other subsidiaries	1,377.0				1,360.2				1,377.0	1,360.2
Notes receivable from subsidiaries	596.2				0				596.2	0
Deferred income taxes	33.7				7.2				33.7	7.2
Other	6.4				6.2				6.4	6.2
Total	4,058.8				3,378.6				4,058.8	3,378.6
Total	4,061.8				3,638.2				4,061.8	3,638.2
Current Liabilities
Notes payable	22.0				9.5				22.0	9.5
Current maturities of long-term debt	287.5				0				287.5	0
Accounts payable to subsidiaries	31.8				31.1				31.8	31.1
Accrued taxes	5.1				0				5.1	0
Accrued interest	7.6				6.4				7.6	6.4
Derivative instruments	0				20.8				0	20.8
Other	2.9				7.1				2.9	7.1
Total	356.9				74.9				356.9	74.9
Deferred Credits and Other Liabilities
Other	6.7				1.4				6.7	1.4
Total	6.7				1.4				6.7	1.4
Common shareholders' equity
Common stock-250,000,000 shares authorized without par value 136,113,954 and 135,636,538 shares issued, stated value	2,330.6				2,324.4				2,330.6	2,324.4
Retained earnings	684.7				626.5				684.7	626.5
Treasury stock-264,567 and 400,889 shares, at cost	(5.6)				(8.9)				(5.6)	(8.9)
Accumulated other comprehensive loss	(49.8)				(56.1)				(49.8)	(56.1)
Total	2,959.9				2,885.9				2,959.9	2,885.9
Cumulative preferred stock $100 par value
Total	39.0				39.0				39.0	39.0
Long-term debt	699.3				637.0				699.3	637.0
Total	3,698.2				3,561.9				3,698.2	3,561.9
Total	4,061.8				3,638.2				4,061.8	3,638.2
Cash Flows from Operating Activities
Net income									174.4	211.7	150.1
Adjustments to reconcile income to net cash from operating activities:
Amortization									11.2	3.9	1.9
Deferred income taxes, net									(18.6)	13.9	(6.1)
Equity in earnings from subsidiaries									(200.8)	(239.3)	(174.7)
Equity in (earnings) loss from discontinued subsidiary									0	0	1.5
Cash flows affected by changes in:
Accounts receivable from subsidiaries									0	2.6	(3.7)
Taxes receivable									(6.3)	0	(4.8)
Accounts payable to subsidiaries									(0.3)	2.2	0.2
Other accounts payable									0	(0.1)	0.1
Accrued taxes									5.2	0	0
Accrued interest									1.2	2.7	1.4
Cash dividends from subsidiaries									148.0	138.6	94.0
Settlement Of Forward Starting Swaps									(26.1)	(6.9)	0
Other									2.1	(0.9)	8.8
Net cash from operating activities									102.6	123.2	85.7
Cash Flows from Investing Activities
Equity contributions to subsidiaries									0	0	(455.0)
Intercompany lending									(347.4)	(248.8)	0
Net money pool lending									1.1	(1.1)	(0.9)
Net cash from investing activities									(346.3)	(249.9)	(455.9)
Cash Flows from Financing Activities
Issuance of common stock									5.9	6.2	219.9
Issuance of long-term debt									349.7	249.9	287.5
Issuance fees									(3.2)	(3.2)	(18.8)
Net change in short-term borrowings									12.5	(10.5)	(10.0)
Dividends paid									(115.1)	(114.2)	(110.5)
Other financing activities									(6.4)	(7.3)	(3.8)
Net cash from financing activities									243.4	120.9	364.3
Net Change in Cash and Cash Equivalents									(0.3)	(5.8)	(5.9)
Cash and Cash Equivalents at Beginning of Year								6.1		6.1			12.0
Cash and Cash Equivalents at End of Year	0				0.3				0	0.3			12.0
Parent Company [Member] | Cumulative Preferred Stock [Member] | Preferred Stock 3 Point 80 [Member]
Cumulative preferred stock $100 par value
Total	10.0				10.0				10.0	10.0
Parent Company [Member] | Cumulative Preferred Stock [Member] | Preferred Stock 4 Point 50 [Member]
Cumulative preferred stock $100 par value
Total	10.0				10.0				10.0	10.0
Parent Company [Member] | Cumulative Preferred Stock [Member] | Preferred Stock 4 Point 20 [Member]
Cumulative preferred stock $100 par value
Total	7.0				7.0				7.0	7.0
Parent Company [Member] | Cumulative Preferred Stock [Member] | Preferred Stock 4 Point 35 [Member]
Cumulative preferred stock $100 par value
Total	$ 12.0				$ 12.0				$ 12.0	$ 12.0