Share-Based Compensation (Stock Option Fair Value) (Details) (USD $)	12 Months Ended
Dec. 31, 2011 numberofyears	Dec. 31, 2010 numberofyears	Dec. 31, 2009 numberofyears
Fair value	$ 6.96	$ 5.11	$ 4.93
Dividend yield	1.80%	2.10%	1.90%
Expected volatility	28.10%	28.00%	36.80%
Risk-free interest rate	2.80%	3.40%	2.40%
Expected option life (in years)	7.0	7.0	7.0

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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