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Pension and Postretirement Health and Life Benefits (Schedule of Net Benefit Costs) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Pension Plan, Defined Benefit [Member]    
Service costs $ 0.9 $ 1.0
Interest costs 8.9 9.3
Expected return on plan assets (gains) (10.5) (12.2)
Net periodic benefit cost (credit) (0.7) (1.9)
Postretirement Health and Life Benefits Plans [Member]    
Service costs 0.0 0.1
Interest costs 2.1 2.2
Expected return on plan assets (gains) (0.1) (0.2)
Amortization of prior service costs (credits), net (0.1) (0.1)
Net periodic benefit cost (credit) $ 1.9 $ 2.0