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Stock-Based Compensation Long-Term Performance Restricted Stock Unit Award Monte Carlo Pricing Model Assumptions (Details) (Restricted Stock Units (RSUs) [Member], USD $)

3 Months Ended

Mar. 31, 2013

Mar. 31, 2012

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Weighted-average fair value

$ 42.13

^[1]

$ 48.23

^[1]

Long Term Performance Restricted Stock Award [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

0.00%

^[2]

Expected volatility

39.10%

Risk-free interest rate

0.30%

Expected term (years)

2 years 6 months 10 days

Weighted-average fair value

$ 44.93

[1]	Restricted stock units granted in 2012 and 2013 do not include awards under the Performance Award Agreement for the respective years, as these awards are not granted until attainment of annual performance goals has been determined at the conclusion of the performance period, which had not occurred as of March 31, 2012 and 2013, respectively.
[2]	The valuation model assumes that dividends are reinvested by the issuing entity on a continuous basis.

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).

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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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