Stock Based Awards and Other Equity Instruments - Summary of RSU Activity For MSUs (Details) - MSUs $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
MSUs outstanding
Unvested outstanding, Beginning balance | shares	213	[1]
Unvested MSUs, Granted | shares	71	[2]
Unvested outstanding, Ending balance | shares	284
Weighted Average Grant-Date Fair Value Per Share
Unvested outstanding, Weighted Average Grant-Date Fair Value Per Share, Beginning balance | $ / shares	$ 30.04	[1]
Weighted Average Grant-Date Fair Value Per Share, Granted | $ / shares	59.40	[2]
Unvested outstanding, Weighted Average Grant-Date Fair Value Per Share, Ending balance | $ / shares	$ 37.41
Aggregate Intrinsic Value
Unvested MSUs outstanding, Aggregate Intrinsic Value | $	$ 12

[1] Represents 213,000 MSUs awarded to the Company’s CEO in November 2017.

[2] MSUs provide for vesting based upon the Company’s total shareholder return, or TSR, performance over the period commencing January 1, 2018 through December 31, 2020 relative to the TSR performance of the Nasdaq Composite Total Return Index. A Monte-Carlo simulation model, which simulated the present value of the potential outcomes of future stock prices and TSR of the Company and the Nasdaq Composite Total Return Index over the performance period, was used to calculate the grant-date fair value of these awards. The estimated grant-date fair value of these awards is being amortized on a straight-line basis over the requisite service period through December 31, 2020. Based upon actual attainment relative to the target performance metric, the grantee has the ability to receive up to 200% of the target number of MSUs originally granted, or to be issued none at all.