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Earnings Per Share | 12 Months Ended
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Dec. 31, 2020
Earnings Per Share [Abstract] |
Earnings Per Share | 8. Earnings Per Share The following table provides a reconciliation between basic and diluted earnings per share for the years ended December 31:
Millions, Except Per Share Amounts | 2020 | 2019 | 2018
Net income | $ | 5,349 | $ | 5,919 | $ | 5,966
Weighted-average number of shares outstanding: |  |  |  |  |  |
Basic |  | 677.3 |  | 703.5 |  | 750.9
Dilutive effect of stock options |  | 0.8 |  | 1.2 |  | 1.9
Dilutive effect of retention shares and units |  | 1.0 |  | 1.4 |  | 1.5
Diluted |  | 679.1 |  | 706.1 |  | 754.3
Earnings per share – basic | $ | 7.90 | $ | 8.41 | $ | 7.95
Earnings per share – diluted | $ | 7.88 | $ | 8.38 | $ | 7.91
Common stock options totaling 0.3 million, 0.5 million, and 0.3 million for 2020, 2019, and 2018, respectively, were excluded from the computation of diluted earnings per share because the exercise prices of these options exceeded the average market price of our common stock for the respective periods, and the effect of their inclusion would be anti-dilutive.

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