Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share Reconciliation [Abstract]
Net income	$ 600	$ 796
Participating share-based awards — allocated income	(5)	(5)
Net income available to common shareholders -- basic	595	791
Net income available to common shareholders -- diluted	$ 595	$ 791
Weighted average shares outstanding, basic (in shares)	254.4	262.9
Weighted average effects of dilutive securities - stock options and performance shares (in shares)	1.5	1.9
Weighted average shares outstanding, diluted (in shares)	255.9	264.8
Net income per common share, basic (in dollars per share)	$ 2.34	$ 3.01
Net income per common share, diluted (in dollars per share)	$ 2.33	$ 2.99