Earnings Per Share

3 Months Ended

Mar. 31, 2012

Earnings Per Share [Abstract]

Earnings Per Share

6.    Earnings Per Share

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

	Three Months Ended March  31,
	2012			2011
Number of common shares outstanding at end of period		462.7			474.7
Effect of using weighted average common shares outstanding		(0.6	)		1.0
Weighted average basic common shares outstanding		462.1			475.7
Dilutive effect of equity-based compensation awards and other contingently issuable shares		1.3			1.9
Weighted average diluted common shares outstanding		463.4			477.6
Potentially issuable shares		17.4			17.9
Number of anti-dilutive potentially issuable shares excluded from diluted common shares outstanding		8.3			6.2