Employee Benefits - Components of Estimated Net Pension and Other Postretirement Benefit Plan Expense (Income) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension expense (income)
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.3	$ 0.6
Interest cost	36.9	44.8
Expected return on plan assets	(60.5)	(61.6)
Amortization, net	7.8	10.2
Net periodic benefit expense (income)	(15.5)	(6.0)
Other postretirement benefits plan expense (income)
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.0	1.2
Interest cost	3.0	4.0
Expected return on plan assets	(3.4)	(3.3)
Amortization, net	(4.0)	(6.7)
Net periodic benefit expense (income)	$ (3.4)	$ (4.8)