Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020		Jun. 30, 2021	Jun. 30, 2020
Numerator:
Net income	$ 591	$ (539)		$ 1,028	$ 1,497
Denominator:
Basic: Weighted-average common shares outstanding	118.4	125.0		119.1	125.7
Effect of potentially dilutive nonqualified stock options and other share-based awards (in shares)	2.8	1.2		2.6	1.5
Diluted: Weighted-average common shares outstanding	121.2	126.2		121.7	127.2
Basic:
Net income (in dollars per share)	$ 4.99	$ (4.31)		$ 8.63	$ 11.91
Diluted:
Net income (in dollars per share)	$ 4.88	$ (4.31)	[1]	$ 8.45	$ 11.77
Options excluded from earnings per share calculation due to their anti-dilutive effect (in shares)				0.0	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.