The following table provides a reconciliation between basic and diluted earnings per share | | Three Months Ended | | Six Months Ended | | | | June 30, | | June 30, | | Millions, Except Per Share Amounts | 2011 | 2010 | | 2011 | 2010 | | Net income | $ | 785 | $ | 711 | | $ | 1,424 | $ | 1,227 | | Weighted-average number of shares outstanding: | | | | | | | | | | | Basic | | 488.4 | | 501.8 | | | 489.0 | | 503.1 | | Dilutive effect of stock options | | 1.4 | | 3.4 | | | 1.4 | | 3.2 | | Dilutive effect of retention shares and units | | 2.6 | | 1.3 | | | 2.9 | | 1.3 | | Diluted | | 492.4 | | 506.5 | | | 493.3 | | 507.6 | | Earnings per share – basic | $ | 1.61 | $ | 1.42 | | $ | 2.91 | $ | 2.44 | | Earnings per share – diluted | $ | 1.59 | $ | 1.40 | | $ | 2.89 | $ | 2.42 | | Stock options excluded as their inclusion would be antidilutive | | 0.6 | | 0.8 | | | 0.5 | | 0.7 |
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