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Condensed Parent Company Financial Statements (Details 6) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2013
Dec. 31, 2012
Financial Instruments    
Long-term debt including current portion, carrying value $ 4,626.7 $ 4,772.9
Long-term debt including current portion, fair value 4,911.8 5,447.3
Carrying Amount [Member] | Wisconsin Energy Corporation [Member]
   
Financial Instruments    
Long-term debt including current portion, carrying value 700.0 700.0
Fair Value [Member] | Wisconsin Energy Corporation [Member]
   
Financial Instruments    
Long-term debt including current portion, fair value $ 749.4 $ 805.9