XML 124 R49.htm IDEA: XBRL DOCUMENT v2.4.0.8
Nuclear Plant (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2014
Mar. 31, 2013
Dec. 31, 2013
Dec. 31, 2012
Investments in decommissioning trust fund [Line Items]        
Cost Basis $ 140.2   $ 138.1  
Gross Unrealized Gains 48.1   47.1  
Gross Unrealized Losses (0.9)   (1.3)  
Fair Value, Nuclear decommissioning trust fund 187.4   183.9 154.7
Weighted average maturity of debt securities (in years) 7      
Realized gains on investments in decommissioning trust fund 0.2 1.5    
Realized losses on investments in decommissioning trust fund (0.1) (0.4)    
Equity Securities [Member]
       
Investments in decommissioning trust fund [Line Items]        
Cost Basis 84.7   83.7  
Gross Unrealized Gains 45.2   44.6  
Gross Unrealized Losses (0.6)   (0.6)  
Fair Value, Nuclear decommissioning trust fund 129.3   127.7  
Debt Securities [Member]
       
Investments in decommissioning trust fund [Line Items]        
Cost Basis 51.4   51.0  
Gross Unrealized Gains 2.9   2.5  
Gross Unrealized Losses (0.3)   (0.7)  
Fair Value, Nuclear decommissioning trust fund 54.0   52.8  
Other Securities [Member]
       
Investments in decommissioning trust fund [Line Items]        
Cost Basis 4.1   3.4  
Gross Unrealized Gains 0   0  
Gross Unrealized Losses 0   0  
Fair Value, Nuclear decommissioning trust fund 4.1   3.4  
Kansas City Power and Light Company [Member]
       
Investments in decommissioning trust fund [Line Items]        
Fair Value, Nuclear decommissioning trust fund $ 187.4   $ 183.9 $ 154.7