Amount of Prior Service Cost and Actuarial Loss Included in Accumulated Other Comprehensive Loss that is Expected to Be Recognized in Net Periodic Benefit Cost (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss, taxes	$ 6.3
Prior service cost, taxes	0.5
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss, taxes	0.4
Prior service cost, taxes	$ (0.1)