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Stock Based Compensation Plans - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Y
Dec. 31, 2011
Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of compensation plans 4    
Minimum required participant age, years 65    
Non cash compensation expense $ 12.4 $ 11.0 $ 11.8
Excess tax benefit on stock options exercised, financing activities 14.6 12.1 7.2
Tax benefit from stock options exercised 15.4 13.3 8.5
Stock Option
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock exercise period, years 10 years    
Vesting period 3 years    
Minimum service period, years 5 years    
Compensation cost not yet recognized 9.2    
Weighted average years for amortization 1 year 6 months    
Non cash compensation expense 12.4 11.0  
Excess tax benefit on stock options exercised, financing activities $ 14.6 $ 12.1 $ 7.2
With 5 Years Of Service | Stock Option
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Minimum required participant age, years 55