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Components of Net Periodic Pension and Postretirement Health and Life Expense (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Pension [Member]
      
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]      
Service Cost $ 7.6 $ 6.2 $ 5.7
Interest Cost 27.4 26.2 26.2
Expected Return on Plan Assets (34.6) (33.7) (33.8)
Amortization of Loss 12.1 6.6 3.4
Amortization of Prior Service Costs 0.3 0.5 0.6
Net Expense 12.8 5.8 2.1
Postretirement Health and Life [Member]
      
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]      
Service Cost 3.8 4.8 4.1
Interest Cost 10.8 10.9 10.0
Expected Return on Plan Assets (9.7) (9.5) (8.3)
Amortization of Loss 8.5 4.8 2.5
Amortization of Prior Service Costs (1.7) (0.1) 0
Amortization of Transition Obligation 0.1 2.5 2.5
Net Expense $ 11.8 $ 13.4 $ 10.8