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Certain Employee Benefit and Stock-Based Compensation Plans (Stock Based Compensation Plan - Option Pricing Assumptions) (Details) (USD $)
9 Months Ended
Sep. 30, 2011
Sep. 30, 2010
Certain Employee Benefit And Stock Based Compensation Plans [Abstract]  
Risk-free interest rate2.80%2.90%
Dividend yield0.60%0.70%
Volatility34.70%32.70%
Expected life5.96.0
Grant- date fair value$ 22.82$ 19.59