Pensions and Postretirement Benefits - Schedule of Net Periodic Benefit Cost (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
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	$ 0.2	$ 1.7	$ 2.2	$ 3.4
Interest cost	2.1	2.7	4.9	5.4
Expected return on plan assets	(2.7)	(3.1)	(6.9)	(6.2)
Amortization of Prior Service Cost	0.1	0.1	0.1	0.1
Amortization of net loss	0.7	2.2	1.4	4.4
Deconsolidation of GST	0	(0.5)	(0.2)	(1.0)
Net periodic benefit cost	0.4	3.1	1.5	6.1
Other Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	0	0.2	0.2	0.4
Interest cost	0.1	0.1	0.2	0.2
Net periodic benefit cost	$ 0.1	$ 0.3	$ 0.4	$ 0.6