Stockholders' Equity - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant (in shares)	12,000,000
Aggregate intrinsic value of stock options outstanding	$ 32	$ 41
Repurchase of common stock (in shares)	895,699
Stock repurchased during period	$ 47
Amount available for further repurchases under stock repurchase program	$ 90
RSAs and RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
PRSAs \| Tranche 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	50.00%

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Percentage of vesting of share-based compensation awards.

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Amount remaining of a stock repurchase plan authorized.

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Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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Equity impact of the value of stock that has been repurchased during the period and has not been retired and is not held in treasury. Some state laws may mandate the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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