Earnings Per Share - Reconciliation of Weighted Average Number of Shares of Common Stock Outstanding In Calculating EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income (loss)	$ 7		$ 69		$ 32		$ 5		$ (84)	[1]	$ 25	[1]	$ 27	[1]	$ 13	[1]	$ 113	$ (19)	$ 120
Denominator:
Weighted average shares used to compute Basic EPS																	138,116	140,445	145,443
Weighted average effect of dilutive securities:
Stock options																	351		1,129
RSUs/MSUs																	1,908		321
Weighted average shares used to compute Diluted EPS																	140,375	140,445	146,893
Basic EPS	$ 0.05	[2]	$ 0.50	[2]	$ 0.23	[2]	$ 0.04	[2]	$ (0.60)	[2]	$ 0.18	[2]	$ 0.19	[2]	$ 0.09	[2]	$ 0.82	$ (0.14)	$ 0.83
Diluted EPS	$ 0.05	[2]	$ 0.49	[2]	$ 0.23	[2]	$ 0.04	[2]	$ (0.60)	[2]	$ 0.18	[2]	$ 0.19	[2]	$ 0.09	[2]	$ 0.81	$ (0.14)	$ 0.82

[1] During the fourth quarter of 2017, we recognized $67 million of Transition Tax and $6 million of tax expense recorded for the remeasurement of our net deferred tax assets related to the 2017 Tax Act enacted on December 22, 2017. Refer to “Note 11: Income Taxes” for further information.

[2] Earnings per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly earnings per share may not equal the total computed for the year.