Earnings Per Share

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Earnings Per Share

9. 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	2019		2018		2017
Net income	$	5,919	$	5,966	$	10,712
Weighted-average number of shares outstanding:
Basic		703.5		750.9		798.4
Dilutive effect of stock options		1.2		1.9		1.8
Dilutive effect of retention shares and units		1.4		1.5		1.5
Diluted		706.1		754.3		801.7
Earnings per share – basic	$	8.41	$	7.95	$	13.42
Earnings per share – diluted	$	8.38	$	7.91	$	13.36

Common stock options totaling 0.5 million, 0.3 million, and 1.6 million for 2019, 2018, and 2017, 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.