Employee Benefits - Components of Estimated Net Pension and Other Postretirement Benefit Plan Expense (Income) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Settlement			$ 96.9
Pension expense (income)
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.3	$ 0.5	0.6	$ 1.1
Interest cost	36.8	44.6	73.7	89.4
Expected return on plan assets	(60.9)	(61.7)	(121.4)	(123.3)
Amortization, net	7.9	10.2	15.7	20.4
Settlement	96.9		96.9
Net periodic benefit expense (income)	81.0	(6.4)	65.5	(12.4)
Other postretirement benefits plan expense (income)
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.0	1.2	2.0	2.4
Interest cost	3.1	4.0	6.1	8.0
Expected return on plan assets	(3.4)	(3.2)	(6.8)	(6.5)
Amortization, net	(4.0)	(6.8)	(8.0)	(13.5)
Net periodic benefit expense (income)	$ (3.3)	$ (4.8)	$ (6.7)	$ (9.6)