Summary of Post-Retirement Plans to Amortize from Accumulated Other Comprehensive Income (Loss) as Net Periodic Expense (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Pension Plans
Schedule of Net Periodic Benefit Costs and Assumptions for Defined Benefit Retirement Plans [Line Items]
Net actuarial losses	$ 11.1
Net prior service costs	0.6
Total to be recognized as components of net periodic expense	11.7
Other Retirement Plans
Schedule of Net Periodic Benefit Costs and Assumptions for Defined Benefit Retirement Plans [Line Items]
Net actuarial losses	0.4
Total to be recognized as components of net periodic expense	$ 0.4