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Share-Based Compensation Plans - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended 1 Months Ended
Mar. 31, 2013
CompensationPlan
Mar. 31, 2013
Performance Restricted Stock Units
Mar. 31, 2012
Performance Restricted Stock Units
Mar. 31, 2013
Plan Of 2012
Apr. 17, 2013
Plan Of 2012
Subsequent Event
Mar. 31, 2013
Directors Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Additional shares authorized         2,000,000  
Number of remaining shares that may be issued       3,373,653   39,259
Number of employee stock purchase programs 2          
Awards requisite service period   3 years        
Fair value assumptions, risk-free interest rate   0.42% 0.41%      
Fair value assumptions, dividend yield   0.81% 0.85%      
Fair value assumptions, expected life in years   2 years 10 months 17 days 2 years 9 months 29 days      
Unrecognized compensation expenses related to share-based payment arrangements $ 101.3          
Weighted-average period of recognizing unrecognized compensation expenses related to share-based compensation, in years 2 years