Earnings per Share (details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings per Share disclosure
Net income	$ 595	$ 664	$ 1,212	$ 1,355
Participating share-based awards - allocated income	(5)	(5)	(9)	(10)
Net income available to common shareholders -- basic	590	659	1,203	1,345
Net income available to common shareholders -- diluted	$ 590	$ 659	$ 1,203	$ 1,345
Weighted average shares outstanding, basic	277.5	290.1	278.6	292.1
Weighted average effects of dilutive securities, stock options and performance shares (in shares)	2.5	3.5	2.6	3.5
Weighted average shares outstanding, diluted	280.0	293.6	281.2	295.6
Net income per common share, basic	$ 2.13	$ 2.27	$ 4.32	$ 4.60
Net income per common share, diluted	$ 2.11	$ 2.24	$ 4.28	$ 4.55