Share Based Payment and Other Benefits (Schedule of Weighted-Average Assumptions Used in the Valuation of Awards) (Details) (USD $)	12 Months Ended
Dec. 31, 2011 years	Dec. 31, 2010 years	Dec. 31, 2009 years
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Risk-free rate of return	2.60%	2.70%	2.50%
Expected term (in years)	6.25	6.25	6.17
Expected volatility	33.70%	32.70%	41.70%
Expected dividend yield	0.20%	0.30%	0.40%
Weighted-average fair value per option granted	$ 89.11	$ 84.62	$ 71.03

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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