Net Income (loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net income	$ 407	$ 1,035
Denominator:
Weighted average shares of common stock - basic	1,010	1,083
Dilutive effect of equity incentive awards (in shares)	19	19
Weighted average shares of common stock - diluted	1,029	1,102
Net income per share:
Net income per share - basic (in usd per share)	$ 0.40	$ 0.96
Income (loss) per share - diluted:
Continuing operations (in usd per share)	0.40	0.94
Net income per share - diluted (in usd per share)	$ 0.40	$ 0.94
Common stock equivalents excluded from income per diluted share because their effect would have been anti-dilutive (in shares)	1	1