Employee Benefits - Components of Estimated Net Pension and Other Postretirement Benefit Plan Income (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Settlements and curtailments				$ 78.8
Pension (income) expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.1	$ 0.3	$ 0.5	0.8
Interest cost	8.0	37.9	23.7	105.3
Expected return on plan assets	(12.7)	(58.2)	(37.6)	(171.2)
Amortization, net	1.9	7.6	5.4	23.4
Settlements and curtailments		1.6		98.0
Pension (income) expense | Discontinued Operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income) expense		10.2		(43.3)
Pension (income) expense | Continuing operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income) expense	(2.7)	(0.6)	(8.0)	13.0
Other postretirement benefits plan income
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.4	1.0	1.0	3.0
Interest cost	2.7	3.1	8.3	9.2
Expected return on plan assets	(3.4)	(3.4)	(10.1)	(10.2)
Amortization, net	(0.7)	(4.0)	(2.2)	(12.0)
Curtailments		(19.7)		(19.7)
Other postretirement benefits plan income | Continuing operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income) expense	$ (1.0)	$ (23.0)	$ (3.0)	$ (29.7)