Capital Stock (Details 4)	12 Months Ended
	Dec. 31, 2011 Y	Dec. 31, 2010 Y	Dec. 31, 2009 Y
Risk-free rate is based on the U S Treasury yield curve
Expected volatility	34.47%	35.02%	38.73%
Expected dividend yields	0.47%	0.60%	0.73%
Expected term (in years)	5.5	5.5	5.5
Risk-free rate	1.95%	2.31%	2.06%