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Long-Term Debt Long-Term Debt Fair Value (Details) (USD $) In Billions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair value of financial instruments [Abstract]
Long-term Debt	$ 3.4	$ 3.0
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	1.9
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair value of financial instruments [Abstract]
Long-term debt fair value	3.7	3.5
Estimate of Fair Value, Fair Value Disclosure [Member] \| Kansas City Power and Light Company [Member]
Fair value of financial instruments [Abstract]
Long-term debt fair value	$ 2.5	$ 2.2

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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