Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income	$ 392	$ 381	$ 722	$ 677	$ 773	$ 1,399
Dividend equivalent payments, basic	0		(2)		(1)	(3)
Dividend equivalent payments, diluted	0		0		(1)	0
Income available to common stockholders, basic	392		720		772	1,396
Income available to common stockholders, diluted	$ 392		$ 722		$ 772	$ 1,399
Weighted-average shares outstanding (in shares)	255.4		264.8		256.3	265.9
Dilutive effect of outstanding options and share-settled awards (in shares)	1.3		2.3		1.4	2.4
Adjusted weighted-average shares outstanding (in shares)	256.7		267.1		257.7	268.3
Basic (in dollars per share)	$ 1.53		$ 2.72		$ 3.01	$ 5.25
Diluted (in dollars per share)	$ 1.53		$ 2.70		$ 3.00	$ 5.21