Share-Based Compensation (Average Fair Value of Stock Option Granted) (Details)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Dividend yield	1.33%	1.43%
Volatility	34.81%	37.38%
Risk-free rate of return	2.45%	2.36%
Expected life, years	5.3	5.1

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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