Employee Benefits - Components of Estimated Net Pension and Other Postretirement Benefit Plan Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension expense (income)
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.2	$ 0.3
Interest cost	7.8	35.1
Expected return on plan assets	(12.3)	(57.7)
Amortization, net	1.7	7.8
Pension expense (income) | Discontinued Operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit expense (income)		11.2
Pension expense (income) | Continuing operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit expense (income)	(2.6)	(3.3)
Other postretirement benefits plan expense (income)
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.3	1.0
Interest cost	2.8	3.0
Expected return on plan assets	(3.4)	(3.4)
Amortization, net	(0.7)	(4.0)
Other postretirement benefits plan expense (income) | Continuing operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit expense (income)	$ (1.0)	$ (3.4)