Nuclear Plant Decommissioning Trust (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
Sep. 30, 2012	Dec. 31, 2011
Nuclear decommissioning trust fund [Roll Forward]
Nuclear decommissioning trust fund, beginning balance	$ 135.3	$ 129.2
Contributions to nuclear decommission trust fund	2.5	3.4
Nuclear decommissioning trust fund earned income, net of fees	2.0	4.8
Net realized gains (losses) on nuclear decommissioning trust fund	0.9	0.3
Net unrealized gains (losses) on nuclear decommissioning trust fund	11.4	(2.4)
Nuclear decommissioning trust fund, ending balance	152.1	135.3
Kansas City Power and Light Company [Member]
Nuclear decommissioning trust fund [Roll Forward]
Nuclear decommissioning trust fund, ending balance	$ 152.1	$ 135.3

This represents total contributions to the decommissioning trust fund during the current period.

No definition available.

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- Definition

This represents income earned, net of fees, on decommissioning trust fund investments during the current period.

+ References

No definition available.

+ Details

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- Definition

This represents the net realized gains (losses) on decommissioning trust fund investments during the current period.

+ References

No definition available.

+ Details

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- Definition

This represents the net unrealized gains (losses) on decommissioning trust fund investments during the current period.

+ References

No definition available.

+ Details

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- Details

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- Definition

Decommission fund to pay for the costs of decontaminating and decommissioning of facilities through collection of revenues derived from utility assessments and government appropriations. Decommission fund investment for the process whereby a power station, at the end of its economic life, is taken permanently out of service and its site made available for other purposes. In the case of a nuclear station this comprises three different states of clearance. Immediately after the final closure, radioactive material such as nuclear fuel and operational waste is removed and the buildings surrounding the reactor shield are dismantled and finally the reactor itself is dismantled.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.12)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 12

-Article 5

+ Details

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