Employee Benefits - Components of Estimated Net Pension and Other Postretirement Benefit Plan Expense (Income) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pension expense (income)
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.3	$ 0.5	$ 0.9	$ 1.6
Interest cost	36.8	44.5	110.5	133.9
Expected return on plan assets	(58.6)	(61.4)	(180.0)	(184.7)
Amortization, net	7.8	10.1	23.5	30.5
Settlements	1.6		98.5
Net periodic benefit expense (income)	(12.1)	(6.3)	53.4	(18.7)
Other postretirement benefits plan expense (income)
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.0	1.1	3.0	3.5
Interest cost	3.1	4.0	9.2	12.0
Expected return on plan assets	(3.4)	(3.3)	(10.2)	(9.8)
Amortization, net	(4.0)	(6.7)	(12.0)	(20.2)
Curtailments	(19.7)		(19.7)
Net periodic benefit expense (income)	$ (23.0)	$ (4.9)	$ (29.7)	$ (14.5)