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Pension and Postretirement Benefit Plans (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 9 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2012
Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]        
Contributions by employer $ 2.8 $ 2.2 $ 7.6 $ 9.4
Pension [Member]
        
Pension and postretirement benefit plans [Abstract]        
Service cost 0.1 0.4 0.5 1.3
Interest cost 3.4 3.5 10.1 10.5
Expected return on plan assets (4.0) (3.8) (12.1) (11.5)
Amortization of [Abstract]        
Unrecognized net loss 1.2 2.0 3.7 6.0
Unrecognized prior service credit 0 0 0 0
Net periodic benefit cost (income) 0.7 2.1 2.2 6.3
Postretirement [Member]
        
Pension and postretirement benefit plans [Abstract]        
Service cost 0 0 0 0
Interest cost 0.1 0.1 0.2 0.3
Expected return on plan assets 0 0 0 0
Amortization of [Abstract]        
Unrecognized net loss 0 0 0 0
Unrecognized prior service credit (0.4) (0.4) (1.1) (1.2)
Net periodic benefit cost (income) $ (0.3) $ (0.3) $ (0.9) $ (0.9)