Nuclear Plant (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010	Jan. 02, 2010
Investments in decommissioning trust fund [Line Items]
Cost Basis	$ 123,100,000		$ 114,600,000
Gross Unrealized Gains	16,800,000		15,700,000
Gross Unrealized Losses	(4,600,000)		(1,100,000)
Fair Value, Nuclear decommissioning trust fund	135,300,000		129,200,000
Weighted average maturity of debt securities	7.0
Realized Gains on investments in decommissioning trust fund	1,000,000		7,300,000	2,800,000
Realized Losses on investments in decommissioning trust fund	(700,000)		(600,000)	(8,300,000)
Nuclear decommissioning trust fund [Abstract]
Nuclear decommissioning trust fund, ending balance	135,300,000		129,200,000
Wolf Creek Unit [Member]
Jointly Owned Utility Plant Interests [Line Items]
Current cost of decommissioning (in 2011 dollars)	630,000,000
Future cost of decommissioning (in 2045-2053 dollars)	2,455,000,000	[1]
Annual escalation factor	3.73%
Annual return on trust assets through 2025	6.89%	[2]
Annual return on trust assets beginning in 2053	1.81%
Nuclear decommissioning trust fund [Abstract]
Industry aggregate limit on nuclear insurance for property claims including accidental outage	3,200,000,000
Amount of insurance against public liability claims resulting from nuclear incidents to the full limit of public liability	12,600,000,000
Maximum available commercial insurance	400,000,000
Remaining balance provided through an industry-wide retrospective assessment program mandated by law	12,200,000,000
Maximum amount able to be assessed to owners	117,500,000
SFP Program-annual amount payable per incident	17,500,000
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	30,900,000
Equity Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	76,500,000		73,400,000
Gross Unrealized Gains	12,300,000		13,100,000
Gross Unrealized Losses	(4,500,000)		(1,000,000)
Fair Value, Nuclear decommissioning trust fund	84,300,000		85,500,000
Nuclear decommissioning trust fund [Abstract]
Nuclear decommissioning trust fund, ending balance	84,300,000		85,500,000
Debt Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	44,200,000		38,100,000
Gross Unrealized Gains	4,500,000		2,600,000
Gross Unrealized Losses	(100,000)		(100,000)
Fair Value, Nuclear decommissioning trust fund	48,600,000		40,600,000
Nuclear decommissioning trust fund [Abstract]
Nuclear decommissioning trust fund, ending balance	48,600,000		40,600,000
Other Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	2,400,000		3,100,000
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Fair Value, Nuclear decommissioning trust fund	2,400,000		3,100,000
Nuclear decommissioning trust fund [Abstract]
Nuclear decommissioning trust fund, ending balance	2,400,000		3,100,000
Kansas City Power and Light Company [Member]
Investments in decommissioning trust fund [Line Items]
Fair Value, Nuclear decommissioning trust fund	135,300,000		129,200,000
Nuclear decommissioning trust fund [Abstract]
Nuclear decommissioning trust fund, beginning balance			112,500,000
Contributions to nuclear decommission trust fund	3,400,000		3,700,000
Nuclear decommissioning trust fund earned income, net of fees	4,800,000		2,000,000
Net realized gains (losses) on nuclear decommissioning trust fund	300,000		6,700,000
Net unrealized gains (losses) on nuclear decommissioning trust fund	(2,400,000)		4,300,000
Nuclear decommissioning trust fund, ending balance	135,300,000		129,200,000
Kansas City Power and Light Company [Member] | Wolf Creek Unit [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	47.00%
Current cost of decommissioning (in 2011 dollars)	296,000,000
Future cost of decommissioning (in 2045-2053 dollars)	1,154,000,000	[1]
Nuclear decommissioning trust fund [Abstract]
Maximum amount able to be assessed to owners	55,200,000
SFP Program-annual amount payable per incident	8,200,000
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	$ 14,500,000

[1] Total future cost over an eight year decommissioning period.

[2] The 6.89% rate of return is through 2025. The rate then systematically decreases through 2053 to 1.81% based on the assumption that the fund's investment mix will become increasingly more conservative as the decommissioning period approaches.