Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share Reconciliation [Abstract]
Net income	$ 827	$ 396	$ 1,387	$ 1,749
Participating share-based awards — allocated income	(6)	(3)	(9)	(12)
Net income available to common shareholders -- basic	821	393	1,378	1,737
Net income available to common shareholders -- diluted	$ 821	$ 393	$ 1,378	$ 1,737
Weighted average shares outstanding, basic (in shares)	253.3	259.2	253.5	261.1
Weighted average effects of dilutive securities - stock options and performance shares (in shares)	1.0	2.6	1.0	2.3
Weighted average shares outstanding, diluted (in shares)	254.3	261.8	254.5	263.4
Net income per common share, basic (in dollars per share)	$ 3.24	$ 1.52	$ 5.44	$ 6.65
Net income per common share, diluted (in dollars per share)	$ 3.23	$ 1.50	$ 5.41	$ 6.59