Net Income (loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Income from continuing operations	$ 27	$ 437	$ 1,062	$ 919
Loss from discontinued operations, net of income taxes	0	(2)	0	(2)
Net income	$ 27	$ 435	$ 1,062	$ 917
Denominator:
Weighted average shares of common stock - basic	1,076	1,144	1,080	1,151
Dilutive effect of equity incentive awards (in shares)	15	5	17	8
Weighted average shares of common stock - diluted	1,091	1,149	1,097	1,159
Income (loss) per share - basic:
Continuing operations (in usd per share)	$ 0.03	$ 0.38	$ 0.98	$ 0.80
Discontinued operations (in usd per share)	0.00	0.00	0.00	0.00
Net income per share - basic (in usd per share)	0.03	0.38	0.98	0.80
Income (loss) per share - diluted:
Continuing operations (in usd per share)	0.02	0.38	0.97	0.79
Discontinued operations (in usd per share)	0.00	0.00	0.00	0.00
Net income per share - diluted (in usd per share)	$ 0.02	$ 0.38	$ 0.97	$ 0.79
Common stock equivalents excluded from income per diluted share because their effect would have been anti-dilutive (in shares)	1	15	16	14