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Stock-Based Compensation Plans - Valuation Assumptions for Grant Date Fair Value of Performance Awards (Detail) (Performance Shares, USD $)
3 Months Ended
Mar. 31, 2014
Performance Shares
 
Schedule Of Assumptions To Estimate Fair Value For Performance Share Unit Awards [Line Items]  
Risk-free interest rate 0.71%
Expected annual volatility 34.00%
Grant date fair value per unit $ 82.60