Stock Based Awards and Other Equity Instruments - Summary of RSU Activity For MSUs (Details) - MSUs - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017
MSUs outstanding
Unvested outstanding, Beginning balance	213
Unvested MSUs, Granted	71	[1]	213	[2]
Unvested outstanding, Ending balance	284		213
Weighted Average Grant-Date Fair Value Per Share
Unvested outstanding, Weighted Average Grant-Date Fair Value Per Share, Beginning balance	$ 30.04
Weighted Average Grant-Date Fair Value Per Share, Granted	59.40	[1]	$ 30.04	[2]
Unvested outstanding, Weighted Average Grant-Date Fair Value Per Share, Ending balance	$ 37.41		$ 30.04
Aggregate Intrinsic Value
Unvested MSUs outstanding, Aggregate Intrinsic Value	$ 15

[1] 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. 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. These MSUs were granted under the 2011 Plan.

[2] Represents 213,000 market-based RSU or MSUs awarded to the Company’s CEO in November 2017. The MSU award provides 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. Based upon actual attainment relative to the target performance metric, the CEO has the ability to receive up to 125% of the target number of MSUs originally granted, or to be issued none at all.