Earnings Per Share

12 Months Ended

Dec. 31, 2012

Earnings Per Share

17.    Earnings Per Share

Basic and diluted earnings per share were computed using the following common share data (shares in millions):

	Years Ended December 31,
	2012			2011		2010
Number of common shares outstanding at year-end		464.2			460.5		475.0
Effect of using weighted average common shares outstanding		(0.6	)		9.2		5.2
Weighted average basic common shares outstanding		463.6			469.7		480.2
Dilutive effect of equity-based compensation awards and other contingently issuable shares		0.8			1.7		2.0
Weighted average diluted common shares outstanding		464.4			471.4		482.2
Potentially issuable shares		15.3			17.0		12.8
Number of anti-dilutive potentially issuable shares excluded from diluted common shares outstanding		7.5			9.8		3.6