Share Based Compensation - Option Grant Information (Details) (Stock Options [Member])	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk Free Interest Rate	2.10%	2.30%	1.60%
Dividend yield	6.10%	7.60%	8.50%
Historical volatility factor	36.60%	35.70%	32.50%
Weighted-average expected life	5	5	5

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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