Income Taxes	3 Months Ended
Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes During the three months ended March 31, 2018, we incurred $223.6 million of income tax expense. In December 2017, the President of the U.S. signed into law the Tax Cuts and Jobs Act (2017 Tax Act), which includes significant changes to the U.S. corporate income tax system, including a reduction in the corporate income tax rate, transition to a territorial tax system, and modifications to the international tax provisions. The changes that became effective January 1, 2018 resulted in a reduction to our tax expense for the three months ended March 31, 2018 compared to the three months ended March 31, 2017. During the three months ended March 31, 2017, we incurred $172.0 million of income tax, despite earning $61.2 million of income before income taxes, as a result of the non-deductible $857.6 million acquired IPR&D charge for the acquisition of CoLucid. At March 31, 2018, our accounting for the 2017 Tax Act is incomplete; however, we expect to complete our accounting by December 2018. As discussed in our 2017 Annual Report on Form 10-K, we recorded provisional adjustments for effects that we were able to reasonably estimate. Those effects included the one-time repatriation transition tax (also known as the 'Toll Tax'), re-measurement of deferred tax assets and liabilities, unremitted earnings, executive compensation, and uncertain tax positions. At year-end, we were not able to make reasonable estimates for Global Intangible Low-Taxed Income (GILTI) deferred taxes or valuation allowances; therefore, we did not record provisional amounts. We are still evaluating the effects of the GILTI provisions and assessing our valuation allowances, and we have not yet determined our accounting policy election with respect to GILTI deferred taxes or the application of intra-entity transfers of inventory; therefore, the estimated annual effective tax rate reflects GILTI as a period expense. For the first quarter of 2018, we have not made any additional measurement-period adjustments related to these provisional items as we are continuing to collect and analyze additional information as well as evaluate the interpretations and assumptions made. Updates to our calculations may result in material changes to the provisional adjustments recorded at year-end and the estimated annual effective tax rate. The U.S. examination of tax years 2013-2015 began in 2016. While we believe it is reasonably possible that this audit could reach resolution within the next 12 months, the IRS examination of tax years 2013-2015 remains ongoing. Therefore, it is not possible to reasonably estimate the change to unrecognized tax benefits and the related future cash flows.

Income Taxes

During the three months ended March 31, 2018, we incurred $223.6 million of income tax expense. In December 2017, the President of the U.S. signed into law the Tax Cuts and Jobs Act (2017 Tax Act), which includes significant changes to the U.S. corporate income tax system, including a reduction in the corporate income tax rate, transition to a territorial tax system, and modifications to the international tax provisions. The changes that became effective January 1, 2018 resulted in a reduction to our tax expense for the three months ended March 31, 2018 compared to the three months ended March 31, 2017. During the three months ended March 31, 2017, we incurred $172.0 million of income tax, despite earning $61.2 million of income before income taxes, as a result of the non-deductible $857.6 million acquired IPR&D charge for the acquisition of CoLucid.

At March 31, 2018, our accounting for the 2017 Tax Act is incomplete; however, we expect to complete our accounting by December 2018. As discussed in our 2017 Annual Report on Form 10-K, we recorded provisional adjustments for effects that we were able to reasonably estimate. Those effects included the one-time repatriation transition tax (also known as the 'Toll Tax'), re-measurement of deferred tax assets and liabilities, unremitted earnings, executive compensation, and uncertain tax positions. At year-end, we were not able to make reasonable estimates for Global Intangible Low-Taxed Income (GILTI) deferred taxes or valuation allowances; therefore, we did not record provisional amounts. We are still evaluating the effects of the GILTI provisions and assessing our valuation allowances, and we have not yet determined our accounting policy election with respect to GILTI deferred taxes or the application of intra-entity transfers of inventory; therefore, the estimated annual effective tax rate reflects GILTI as a period expense. For the first quarter of 2018, we have not made any additional measurement-period adjustments related to these provisional items as we are continuing to collect and analyze additional information as well as evaluate the interpretations and assumptions made. Updates to our calculations may result in material changes to the provisional adjustments recorded at year-end and the estimated annual effective tax rate.

The U.S. examination of tax years 2013-2015 began in 2016. While we believe it is reasonably possible that this audit could reach resolution within the next 12 months, the IRS examination of tax years 2013-2015 remains ongoing. Therefore, it is not possible to reasonably estimate the change to unrecognized tax benefits and the related future cash flows.