Earnings per share

12 Months Ended

Dec. 31, 2011

Notes To Financial Statements [Abstract]

Earnings per share

16 – Earnings per share

	Year ended December 31,		2011		2010		2009
Basic earnings per share		$	5.45	$	4.51	$	3.95
Diluted earnings per share		$	5.41	$	4.48	$	3.92
The following table provides a reconciliation between basic and diluted earnings per share:
In millions	Year ended December 31,		2011		2010		2009
Net income		$	2,457	$	2,104	$	1,854
Weighted-average shares outstanding			451.1		466.3		469.2
Effect of stock options			3.3		3.8		4.3
Weighted-average diluted shares outstanding			454.4		470.1		473.5

Basic earnings per share are calculated based on the weighted-average number of common shares outstanding over each period. Diluted earnings per share are calculated based on the weighted-average diluted shares outstanding using the treasury stock method, which assumes that any proceeds received from the exercise of in-the-money stock options would be used to purchase common shares at the average market price for the period.For the years ended December 31, 2011, 2010 and 2009, the weighted-average number of stock options that were not included in the calculation of diluted earnings per share, as their inclusion would have had an anti-dilutive impact, were 0.1million, nil and 0.4 million, respectively.