Pensions and Postretirement Benefit Plans - Components of Net Periodic Benefit Cost for Pension Plans and Other Benefit Plans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Postemployment Benefits [Abstract]
Service cost	$ 0.6	$ 0.8	$ 1.2	$ 1.7
Interest cost	3.1	2.6	6.0	5.3
Expected return on plan assets	(3.5)	(3.1)	(7.0)	(6.3)
Amortization of prior service cost	(0.1)	0.1	(0.1)	0.1
Amortization of net loss	1.0	1.9	2.0	3.8
Net periodic benefit cost	1.1	2.3	2.1	4.6
Defined contribution plan expense	1.5	1.4	3.2	2.9
Other postretirement benefit plans	0.1	0.2	0.2	0.3
Multi-employer pension plan expense	$ 0.1	$ 0.1	$ 0.2	$ 0.2