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Share-Based Payments (Weighted Average Assumptions for Employee Stock Purchase Plan and other Option Plans) (Details)
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Employee Stock Purchase Plan [Member]
     
Risk-free interest rate 0.13% 0.20% 0.31%
Expected term 6 6 6
Dividend yield 3.00% 3.30% 3.40%
Expected volatility 19.00% 28.00% 64.00%
Stock Option [Member]
     
Risk-free interest rate 0.00% 2.30% 1.85%
Expected term   5 5
Dividend yield 0.00% 3.30% 3.90%
Expected volatility 0.00% 34.00% 32.00%