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Summary of Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets (Detail) (Pension Benefits, USD $)
In Millions, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Pension Benefits
   
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligation $ 400.0 $ 379.3
Fair value of plan assets $ 272.8 $ 250.7