Retirement Plans and Other Post-Retirement Benefits - Schedule of Net Periodic Benefit Cost of Pension and Other Benefits (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]
Service cost	$ 10.5	$ 11.6	$ 10.4
Interest cost	24.5	23.3	24.8
Expected return on plan assets	(45.4)	(46.0)	(43.9)
Amortization of prior service cost/(credit)	2.7	3.1	3.3
Amortization of actuarial loss	13.2	17.1	12.1
One-time settlement charge	7.3
Total net periodic benefit cost	12.8	9.1	6.7
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.1	1.4	1.5
Interest cost	2.0	2.0	2.5
Amortization of prior service cost/(credit)	(0.2)	(0.3)	(0.3)
Amortization of actuarial loss	(0.8)	0.2	0.4
Total net periodic benefit cost	$ 2.1	$ 3.3	$ 4.1