Stock Based Compensation Plans, Weighted average assumptions (Details) (USD $)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Weighted average fair value assumptions [Abstract]
Stock price (in dollars per share)	$ 131.87	$ 107.21
Stock price, minimum (in dollars per share)			$ 66.05
Stock price, maximum (in dollars per share)			$ 84.90
Risk-free interest rates (in hundredths)	2.24%	3.50%	4.58%
Expected lives (in years)	10	10	10
Volatility (in hundredths)	19.63%	22.00%	20.00%

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.

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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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