Net Income (loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Income from continuing operations	$ 638	$ 29	$ 1,045	$ 1,064
Income from discontinued operations, net of income taxes	4	0	4	0
Net income	$ 642	$ 29	$ 1,049	$ 1,064
Denominator:
Weighted average shares of common stock - basic	992	1,076	1,001	1,080
Dilutive effect of equity incentive awards (in shares)	12	15	15	17
Weighted average shares of common stock - diluted	1,004	1,091	1,016	1,097
Income per share - basic:
Continuing operations (in usd per share)	$ 0.64	$ 0.03	$ 1.04	$ 0.99
Discontinued operations (in usd per share)	0	0	0	0
Net income per share - basic (in usd per share)	0.64	0.03	1.04	0.99
Income per share - diluted:
Continuing operations (in usd per share)	0.64	0.03	1.03	0.97
Discontinued operations (in usd per share)	0	0	0	0
Net income per share - diluted (in usd per share)	$ 0.64	$ 0.03	$ 1.03	$ 0.97
Common stock equivalents excluded from income per diluted share because their effect would have been anti-dilutive (in shares)	15	1	13	16