Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share Reconciliation [Abstract]
Net income	$ 796	$ 669
Participating share-based awards — allocated income	(5)	(5)
Net income available to common shareholders -- basic	791	664
Net income available to common shareholders -- diluted	$ 791	$ 664
Weighted average shares outstanding, basic (in shares)	262.9	271.0
Weighted average effects of dilutive securities - stock options and performance shares (in shares)	1.9	2.9
Weighted average shares outstanding, diluted (in shares)	264.8	273.9
Net income per common share, basic (in dollars per share)	$ 3.01	$ 2.45
Net income per common share, diluted (in dollars per share)	$ 2.99	$ 2.42