Retirement Plans and Other Post-Retirement Benefits - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial (gain) loss	$ 1.4	$ 21.5
Plan amendments	5.5
Recognized prior service cost	(2.7)	(3.1)	$ (3.3)
Recognized actuarial losses	(20.5)	(17.1)
Total recognized in other comprehensive (income) loss	(16.3)	1.3
Total recognized in net periodic benefit cost and other comprehensive (income) loss	(3.5)	10.4
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial (gain) loss	(3.4)	(10.1)
Recognized prior service cost	0.2	0.3	$ 0.3
Recognized actuarial losses	0.8	(0.2)
Total recognized in other comprehensive (income) loss	(2.4)	(10.0)
Total recognized in net periodic benefit cost and other comprehensive (income) loss	$ (0.3)	$ (6.7)