Share-Based Compensation (Schedule of Weighted Average Assumptions Used in Valuing Stock Options Granted to Employees) (Details)	12 Months Ended
Dec. 31, 2011 Y	Dec. 31, 2010 Y	Dec. 31, 2009 Y
Share-based Compensation [Abstract]
Stock price volatility	34.00%	31.00%	40.00%
Risk-free interest rate	1.88%	2.12%	2.13%
Expected life (in years)	4.97	4.84	5.01
Dividend rate	0.00%	0.00%	0.00%
Forfeiture rate	6.10%	7.00%	7.70%

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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