Income per Share

9 Months Ended

Sep. 30, 2012

Earnings Per Share [Abstract]

Income per Share

Income per Share

Basic income per share is based on the weighted average number of common shares outstanding during the period. Diluted income per share includes additional common shares that would have been outstanding if potential common shares with a dilutive effect had been issued.

A reconciliation of the number of shares used for the basic and diluted income per share calculations is as follows:

	Three Months Ended September 30		Nine Months Ended September 30
Millions of shares	2012	2011	2012	2011
Basic weighted average common shares outstanding	928	920	925	917
Dilutive effect of employee stock plans	2	5	2	5
Diluted weighted average common shares outstanding	930	925	927	922

Excluded from the computation of diluted income per share are options to purchase seven million shares of common stock that were outstanding during both the three and nine months endedSeptember 30, 2012 and four million and one million shares that were outstanding during the three and nine months endedSeptember 30, 2011. These options were outstanding during these periods but were excluded because they were antidilutive, as the option exercise price was greater than the average market price of the common shares.