Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020		Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net income	$ 1,031	$ (140)		$ 2,059	$ 1,357
Denominator:
Basic: Weighted-average common shares outstanding	116.4	123.0		118.2	124.8
Effect of potentially dilutive nonqualified stock options and other share-based awards (in shares)	2.8	1.9		2.7	1.7
Diluted: Weighted-average common shares outstanding	119.2	124.9		120.9	126.5
Basic:
Net income (in dollars per share)	$ 8.86	$ (1.14)		$ 17.42	$ 10.87
Diluted:
Net income (in dollars per share)	$ 8.65	$ (1.14)	[1]	$ 17.03	$ 10.73
Options excluded from earnings per share calculation due to their anti-dilutive effect (in shares)		1.5

[1] Diluted shares used in this calculation represent basic shares due to the net loss. Using actual diluted shares would result in anti-dilution.