Employee Benefits - Components of Estimated Net Pension and Other Postretirement Benefit Plan Income (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension expense (income)
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.2	$ 0.2	$ 0.4	$ 0.5
Interest cost	7.9	32.3	15.7	67.4
Expected return on plan assets	(12.6)	(55.3)	(24.9)	(113.0)
Amortization, net	1.8	8.0	3.5	15.8
Settlements and curtailments		96.4		96.4
Pension expense (income) | Discontinued Operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit expense (income)		(64.7)		(53.5)
Pension expense (income) | Continuing operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit expense (income)	(2.7)	16.9	(5.3)	13.6
Other postretirement benefits plan expense (income)
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.3	1.0	0.6	2.0
Interest cost	2.8	3.1	5.6	6.1
Expected return on plan assets	(3.3)	(3.4)	(6.7)	(6.8)
Amortization, net	(0.8)	(4.0)	(1.5)	(8.0)
Other postretirement benefits plan expense (income) | Continuing operations
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit expense (income)	$ (1.0)	$ (3.3)	$ (2.0)	$ (6.7)