v3.5.0.2
Employee Retirement Plans - Schedule of Components of Net Periodic Benefit Income (Expense) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Pension Benefits [Member]      
Components of net periodic benefit income (expense):      
Interest cost $ (30.7) $ (31.7) $ (28.0)
Service cost (4.3) (3.6) (6.6)
Expected return on assets 45.2 47.0 38.5
Amortization of actuarial gain (loss) (2.6) 0.4 (2.1)
Total amortization (2.6) 0.4 (2.1)
Settlement loss   (5.8)  
Curtailment gain     15.5
Other components of net periodic pension cost   (0.5)  
Total net periodic benefit income (expense) 7.6 5.8 17.3
OPEB Benefits [Member]      
Components of net periodic benefit income (expense):      
Interest cost (3.5) (4.4) (6.4)
Service cost (0.9) (0.8) (2.0)
Amortization of prior service credit 10.2 9.2 2.3
Amortization of actuarial gain (loss) (0.1) (0.1)  
Total amortization 10.1 9.1 2.3
Total net periodic benefit income (expense) $ 5.7 $ 3.9 $ (6.1)