Share-Based Compensation Plans (Details 5) (USD $)	12 Months Ended
Dec. 31, 2011 Y	Dec. 31, 2010 Y	Dec. 31, 2009 Y
Stock Option [Member]
Weighted-average assumptions used for options granted
Expected dividends	2.20%	3.00%	2.80%
Expected volatility	38.70%	43.90%	46.40%
Risk-free interest rate	1.70%	1.70%	1.50%
Expected term in years	3.6	3.4	3.1
Grant-date fair value	$ 12.88	$ 8.93	$ 9.26
Employee Stock Purchase Plan [Member]
Weighted-average assumptions used for options granted
Expected dividends	2.40%	2.50%	2.80%
Expected volatility	32.80%	35.60%	67.60%
Risk-free interest rate	0.10%	0.20%	0.20%
Expected term in years	0.25	0.25	0.25
Grant-date fair value	$ 10.21	$ 8.95	$ 9.43

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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