Fair Value Measurements	12 Months Ended
Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Under applicable accounting guidance, fair value is defined as the exit price, or the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants as of the measurement date. Applicable accounting guidance also establishes a valuation hierarchy for inputs in measuring fair value that maximizes the use of observable inputs (inputs market participants would use based on market data obtained from sources independent of the Company) and minimizes the use of unobservable inputs (inputs that reflect the Company's assumptions based upon the best information available in the circumstances) by requiring the most observable inputs be used when available. Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities. Level 2 inputs are quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and inputs (other than quoted prices) that are observable for the assets or liabilities, either directly or indirectly. Level 3 inputs are unobservable inputs for the assets or liabilities. Categorization within the hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The Company used foreign currency forward contracts as effective economic hedges to manage a portion of its foreign currency exposure, the last of which expired in December 2017. Foreign currency forward contracts involve the purchase and sale of a designated currency at an agreed upon rate for settlement on a specified date. The aggregate notional value of these foreign currency contracts was $427 million as of December 31, 2016. As these derivatives were not designated and/or did not qualify for hedge accounting, the changes in fair value were recognized as other income (expense) in the accompanying consolidated statements of operations. For the years ended December 31, 2017 and 2016, the Company recorded in other income (expense) a $12 million loss and $10 million gain, respectively, related to the change in fair value of the forward contracts. Cash equivalents, which are short-term investments with original maturities of less than 90 days, had an estimated fair value of $2.64 billion and $1.05 billion as of December 31, 2018 and 2017, respectively. The estimated fair value of the Company's cash equivalents is based on level 1 inputs (quoted market prices in active markets).

Fair Value Measurements

Under applicable accounting guidance, fair value is defined as the exit price, or the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants as of the measurement date. Applicable accounting guidance also establishes a valuation hierarchy for inputs in measuring fair value that maximizes the use of observable inputs (inputs market participants would use based on market data obtained from sources independent of the Company) and minimizes the use of unobservable inputs (inputs that reflect the Company's assumptions based upon the best information available in the circumstances) by requiring the most observable inputs be used when available. Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities. Level 2 inputs are quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and inputs (other than quoted prices) that are observable for the assets or liabilities, either directly or indirectly. Level 3 inputs are unobservable inputs for the assets or liabilities. Categorization within the hierarchy is based upon the lowest level of input that is significant to the fair value measurement.

The Company used foreign currency forward contracts as effective economic hedges to manage a portion of its foreign currency exposure, the last of which expired in December 2017. Foreign currency forward contracts involve the purchase and sale of a designated currency at an agreed upon rate for settlement on a specified date. The aggregate notional value of these foreign currency contracts was $427 million as of December 31, 2016. As these derivatives were not designated and/or did not qualify for hedge accounting, the changes in fair value were recognized as other income (expense) in the accompanying consolidated statements of operations. For the years ended December 31, 2017 and 2016, the Company recorded in other income (expense) a $12 million loss and $10 million gain, respectively, related to the change in fair value of the forward contracts.

Cash equivalents, which are short-term investments with original maturities of less than 90 days, had an estimated fair value of $2.64 billion and $1.05 billion as of December 31, 2018 and 2017, respectively. The estimated fair value of the Company's cash equivalents is based on level 1 inputs (quoted market prices in active markets).