Net Income Per Share - Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net income	$ 823	$ 667	$ 526	$ 511	$ 1,490	$ 1,037
Denominator:
Weighted average shares of common stock - basic (in shares)	1,175		1,187		1,173	1,190
Dilutive effect of equity incentive awards (in shares)	12		15		15	19
Weighted average shares of common stock - diluted (in shares)	1,187		1,202		1,188	1,209
Net income per share:
Basic (in usd per share)	$ 0.70		$ 0.44		$ 1.27	$ 0.87
Diluted (in usd per share)	$ 0.69		$ 0.44		$ 1.25	$ 0.86
Common stock equivalents excluded from income per diluted share because their effect would have been anti-dilutive (in shares)	0		1		2	1