Stock-Based Compensation (Details 2)	12 Months Ended
Dec. 31, 2011 Y	Dec. 31, 2010 Y	Dec. 31, 2009 Y
Stock Options [Member]
Weighted average assumptions in valuation model
Expected holding period (in years)	5.2	4.7	4.6
Expected volatility	26.40%	26.20%	26.20%
Expected dividend yield	2.80%	2.20%	2.40%
Risk-free interest rate	2.20%	2.30%	2.50%
TSR [Member]
Weighted average assumptions in valuation model
Expected volatility	25.00%	27.90%
Expected dividend yield	2.70%	2.70%
Risk-free interest rate	0.30%	0.10%

The period of time an equity-based award is expected to be outstanding. An equity-based award's expected term is generally determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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