Stock-Based Compensation Plans - Weighted Average Grant Date Fair Value of SARs (Detail) (Stock Appreciation Rights (SARs), USD $)	3 Months Ended
Mar. 31, 2013
Stock Appreciation Rights (SARs)
Schedule Of Weighted Average Assumptions For Fair Values Of Stock Options [Line Items]
Weighted average exercise price per share	$ 69.23
Expected annual dividends per share	0.23%
Expected life in years	3 years 8 months 12 days
Expected volatility	34.00%
Risk-free interest rate	0.60%
Granted	$ 18.41

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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