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Share-Based Compensation (Weighted Average Assumptions Used) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (years)	6 years 2 months 12 days	6 years 2 months 12 days	6 years 1 month 6 days
Expected volatility	41.90%	40.00%	43.30%
Expected dividend yield	1.01%	1.04%	0.19%
Risk-free interest rate	2.11%	3.36%	3.75%
Weighted-average fair value per option	$ 19.91	$ 20.83	$ 16.73

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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