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Stock-Based Compensation (Weighted Average Assumptions Used in Calculating Fair Value of Stock Option) (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk free interest rate	1.30%	2.90%	2.80%
Expected life of option in years	6 years 6 months 0 days	6 years 4 months 24 days	5 years 10 months 24 days
Expected dividend yield	3.30%	3.30%	3.40%
Expected volatility	29.40%	28.00%	28.50%

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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