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