Funded Status of Plans (Detail) (Postretirement Benefits, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Projected benefit obligation, beginning of period	$ 46.0	$ 45.8
Service cost	0.1	0.1	0.1
Interest cost	2.1	2.4	2.7
Net actuarial (gains) losses	(0.2)	0.4
Benefits paid	(2.8)	(2.7)
Projected benefit obligation, end of year	45.2	46.0	45.8
Fair value of plan assets, end of year
Funded status of plans	$ (45.2)	$ (46.0)