| 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 (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended | 
|---|---|
| Dec. 31, 2012 | |
| Pension Benefits | |
| Defined Benefit Plan Disclosure [Line Items] | |
| Actuarial loss, net of taxes of $6.3 for pension benefits and and $0.4 for other benefits | $ 10.8 | 
| Prior service cost, net of taxes of $0.5 for pension benefits and and $(0.1) for other benefits | 0.8 | 
| Other Benefits | |
| Defined Benefit Plan Disclosure [Line Items] | |
| Actuarial loss, net of taxes of $6.3 for pension benefits and and $0.4 for other benefits | 0.6 | 
| Prior service cost, net of taxes of $0.5 for pension benefits and and $(0.1) for other benefits | $ (0.1) | 
| X | ||||||||||
| 
- Definition Defined Benefit Plan, Actuarial Losses to be Amortized and Reclassified from Accumulated Other Comprehensive Income (Loss) to Net Pension Cost No definition available. 
 | 
| X | ||||||||||
| 
- Definition Defined Benefit Plan, Prior Service Cost to be Amortized and Reclassified from Accumulated Other Comprehensive Income (Loss) to Net Pension Cost No definition available. 
 | 
| X | ||||||||||
| 
- Details 
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