Pension and Postretirement Benefit Plans - Company's Share of Net Periodic Cost Components (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 [Member]
Pension And Other Employee Benefit Plans [Line Items]
Service cost	$ 1.3	$ 1.5	$ 2.6	$ 3.0
Interest cost	2.8	2.4	5.6	4.8
Expected return on plan assets	(3.1)	(3.0)	(6.3)	(6.0)
Amortization of:
Prior service benefits	0	0	0	0
Net actuarial loss	2.1	2.0	3.5	4.0
Net periodic cost (benefit)	3.1	2.9	5.4	5.8
Postretirement [Member]
Pension And Other Employee Benefit Plans [Line Items]
Service cost	0	0	0	0.1
Interest cost	0.2	0.3	0.5	0.6
Expected return on plan assets	0	0	0	0
Amortization of:
Prior service benefits	(1.4)	(1.4)	(2.8)	(2.8)
Net actuarial loss	0.1	0.3	0.3	0.6
Net periodic cost (benefit)	$ (1.1)	$ (0.8)	$ (2.0)	$ (1.5)