XML 21 R70.htm IDEA: XBRL DOCUMENT

Assumptions Used To Estimate Fair Value of Stock Option Grants (Detail) (Stock Options, USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Options
Share Based Compensation [Line Items]
Dividend yield	0.80%	0.80%	0.90%
Risk-free interest rate	0.90%	1.03%	1.29%
Expected option life in years	7 years	7 years	7 years 2 months 12 days
Expected volatility	21.00%	23.00%	23.00%
Option fair value	$ 20.22	$ 19.82	$ 21.34

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.

+ References+ Details