Share-Based Compensation (Details) (Market Measure-Based Restricted Stock Units (RSUs) [Member], USD $)	12 Months Ended
Dec. 31, 2012
Market Measure-Based Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value per share	$ 41.20
Expected share price volatility	31.00%
Risk-free interest rate	1.60%
Dividend yield	3.80%
Expected life	7 years

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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