Share-Based Payments (Details 6) (USD $)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Assumptions used in valuation of market based stock units
Expected dividend yield	0.00%	0.00%	0.00%
Range of expected stock price volatility	0.00%	30.80%	39.30%
Market stock units [Member]
Assumptions used in valuation of market based stock units
Expected dividend yield	0.00%	0.00%
Minimum range of risk-free interest rates	0.30%	0.30%
Maximum range of risk-free interest rates	1.90%	2.00%
60 calendar day average stock price on grant date minimum	66.78	49.08
60 calendar day average stock price on grant date maximum	101.16	54.12
Weighted average grant date fair value	74.19	61.87
Market stock units [Member] \| Maximum [Member]
Assumptions used in valuation of market based stock units
Range of expected stock price volatility	33.40%	38.80%
Market stock units [Member] \| Minimum [Member]
Assumptions used in valuation of market based stock units
Range of expected stock price volatility	25.70%	28.30%

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ 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