Stock-Based Compensation (Schedule of Assumptions Used to Estimate Weighted-Average Fair Value of Options Granted) (Details)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-based Compensation [Abstract]
Dividend yield	5.00%	5.00%	5.60%
Volatility	12.54%	14.77%	19.81%
Risk-free interest rate	2.26%	2.74%	2.39%
Expected life - years	6.3	6.4	6.6

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.

+ References+ Details

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.

+ References+ Details