Information Regarding Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension Costs
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.3	$ 0.2	$ 0.6	$ 0.5
Interest cost	1.0	1.1	2.0	2.1
Expected return on plan assets	(1.0)	(1.0)	(2.0)	(1.9)
Amortization of prior service cost	0.2	0.2	0.4	0.3
Net periodic benefit cost	0.5	0.5	1.0	1.0
Nonpension Postretirement Costs
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1	0.2	0.2
Interest cost	0.3	0.3	0.6	0.6
Amortization of prior service cost	(0.3)	0	(0.2)	0.1
Net periodic benefit cost	$ 0.1	$ 0.4	$ 0.6	$ 0.9