Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	3. Income Taxes Our effective tax rates for the nine months ended September 30, 2019 and 2018 were 17% and 19%, respectively. The decrease in the effective tax rate for the nine months ended September 30, 2019 as compared to the same period in 2018 was primarily due to an increase in net favorable U.S. tax permanent differences and a net tax benefit from income tax audits concluded during the period, partially offset by a deferred tax benefit recognized in the second quarter of 2018 and an unfavorable impact from our geographic mix of taxable income. The deferred tax benefit recognized in the second quarter of 2018 was recorded as a result of our decision to elect to utilize our net operating loss carryforwards (“NOLs”) to offset the impacts of the transition tax imposed by U.S. tax reform. The difference between our effective tax rates and the U.S. federal statutory income tax rate primarily results from our geographic mix of taxable income in various tax jurisdictions, tax permanent differences and tax credits. We recognize liabilities when we believe that an uncertain tax position may not be fully sustained upon examination by the tax authorities. This evaluation requires significant judgment, the use of estimates, and the interpretation and application of complex tax laws. When facts and circumstances change, we reassess these probabilities and record any changes in the consolidated financial statements as appropriate. In the three and nine months ended September 30, 2019, our tax reserves decreased by an immaterial amount and by $19 million, respectively, due to income tax audits concluded across our jurisdictions. Our net unrecognized tax benefits, excluding interest and penalties, included in our consolidated balance sheets, were $50 million and $69 million as of September 30, 2019 and December 31, 2018, respectively. Tax Receivable Agreement Immediately prior to the closing of our initial public offering in April 2014, we entered into the Tax Receivable Agreement (the "TRA"), which provides the right to receive future payments from us to stockholders and equity award holders that were our stockholders and equity award holders, respectively, immediately prior to the closing of our initial public offering (collectively, the “Pre-IPO Existing Stockholders”). The future payments will equal 85% of the amount of cash savings, if any, in U.S. federal income tax that we and our subsidiaries realize as a result of the utilization of certain tax assets attributable to periods prior to our initial public offering, including NOLs, capital losses and the ability to realize tax amortization of certain intangible assets (collectively, the “Pre-IPO Tax Assets”). Consequently, stockholders who are not Pre-IPO Existing Stockholders will only be entitled to the economic benefit of the Pre-IPO Tax Assets to the extent of our continuing 15% interest in those assets. These payment obligations are our obligations and not obligations of any of our subsidiaries. The actual utilization of the Pre-IPO Tax Assets, as well as the timing of any payments under the TRA, will vary depending upon a number of factors, including the amount, character and timing of our and our subsidiaries’ taxable income in the future. As of September 30, 2019 and December 31, 2018, the current portion of our TRA liability totaled $72 million and $104 million, respectively. As of September 30, 2019 and December 31, 2018, $1 million and $73 million, respectively, are included in other noncurrent liabilities in our consolidated balance sheets. We expect a majority of the future payments under the TRA to be made by January 2020. We made payments of $105 million and $60 million for the nine months ended September 30, 2019 and for the nine months ended September 30, 2018, respectively, which included accrued interest of approximately $3 million and $1 million in the same respective periods. Payments under the TRA are not conditioned upon the parties’ continuing ownership of the company. Changes in the utility of the Pre-IPO Tax Assets will impact the amount of the liability recorded in respect of the TRA. Changes in the utility of these Pre-IPO Tax Assets are recorded in income tax expense and any changes in the obligation under the TRA are recorded in other expense.