Legal Proceedings (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Total Wolf Creek including KCPL [Member] | Positive Outcome of Litigation [Member] | Spent Nuclear Fuel and Radioactive Waste [Member]
Gain Contingencies [Line Items]
Amount of pending claims against the United States in the U.S. Court	$ 14.1
Amount awarded but subject to appeal	10.6
Additional amount awarded upon appeal	2.1
Kansas City Power and Light Company [Member] | Positive Outcome of Litigation [Member] | Spent Nuclear Fuel and Radioactive Waste [Member]
Gain Contingencies [Line Items]
Amount awarded but subject to appeal	5.0
Additional amount awarded upon appeal	1.0
Pending or Threatened Litigation [Member] | Kcpl Greater Missouri Operations Member | Price Reporting Litigation [Member]
Loss Contingencies [Line Items]
Approximate amount of refunds received as a net purchaser of power through settlements with sellers of power	8.0
Estimated additional refunds entitled to receive	12.0
Amount of claims addressed under refund proceedings	$ 5.1