Stock plans (Details)	12 Months Ended
Dec. 31, 2009	Dec. 31, 2008
Options, weighted average assumptions
Weighted average risk free interest rate	3.90%	3.50%
Weighted average dividend yield	3.70%	3.20%
Expected life (years)	2	7
Expected volatility	34.60%	30.00%

The period of time an equity-based award is expected to be outstanding. An equity-based award's expected term is generally determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior.

+ References+ Details

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