XML 77 R57.htm IDEA: XBRL DOCUMENT v3.4.0.3
Derivative Instruments (Details) - USD ($)
$ in Millions
Mar. 31, 2016
Dec. 31, 2015
Futures contracts [Member] | Not Designated as Hedging Instrument [Member]    
Price Risk Derivatives [Abstract]    
Notional Contract Amount $ 30.9 $ 26.6
Fair Value (5.3) (5.7)
Forward Contracts [Member] | Not Designated as Hedging Instrument [Member]    
Price Risk Derivatives [Abstract]    
Notional Contract Amount 13.2 15.6
Fair Value 2.9 3.1
Transmission Congestion Rights [Member] | Not Designated as Hedging Instrument [Member]    
Price Risk Derivatives [Abstract]    
Notional Contract Amount 2.3 5.6
Fair Value (0.2) (0.5)
Kansas City Power and Light Company [Member] | Futures contracts [Member] | Not Designated as Hedging Instrument [Member]    
Price Risk Derivatives [Abstract]    
Notional Contract Amount 1.5 0.9
Fair Value (0.2) (0.1)
Kansas City Power and Light Company [Member] | Transmission Congestion Rights [Member] | Not Designated as Hedging Instrument [Member]    
Price Risk Derivatives [Abstract]    
Notional Contract Amount 1.7 4.1
Fair Value $ (0.1) $ (0.4)
KCPL Greater Missouri Operations [Member]    
Price Risk Derivatives [Abstract]    
Percentage of expected on peak natural gas and natural gas equivalent purchased power price exposure hedged remainder of fiscal year 61.00%  
Percentage of expected on peak natural gas and natural gas equivalent purchased power price exposure hedged year two 35.00%  
Percentage of expected on peak natural gas and natural gas equivalent purchased power price exposure hedged year three 11.00%