Income Taxes	3 Months Ended
Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes We manage our affairs so that we are centrally managed and controlled in the U.K. and therefore have our tax residency in the U.K. The provision for income taxes consists of provisions for U.K. and international income taxes. We operate in an international environment with operations in various locations outside the U.K. Accordingly, the consolidated income tax rate is a composite rate reflecting the earnings in the various locations and the applicable rates. The effective income tax rate for the three months ended March 31, 2018 was 20.9%, compared to 22.1% for 2017. We continue to actively pursue initiatives to reduce our effective tax rate. The tax rate in any quarter can be affected positively or negatively by adjustments that are required to be reported in the specific quarter of resolution. The liability for uncertain tax positions was $35.3 million and $36.6 million at March 31, 2018 and December 31, 2017, respectively. We record penalties and interest related to unrecognized tax benefits in Provision for income taxes and Net interest expense, respectively, on the Condensed Consolidated Statements of Operations and Comprehensive Income, which is consistent with our past practices. U.S. tax reform On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the “Act”) was signed into law making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a corporate tax rate decrease from 35% to 21% effective for tax years beginning after December 31, 2017, the transition of U.S. international taxation from a worldwide tax system to a territorial system, and a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings as of December 31, 2017. Given the significance of the Act, Staff Accounting Bulletin No. 118 ("SAB 118") was issued to address the application of GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Act. SAB 118 allows registrants to record provisional amounts during a one year “measurement period.” The measurement period is deemed to have ended when the registrant has obtained, prepared, and analyzed the information necessary to finalize its accounting. During the measurement period, impacts of the law are expected to be recorded at the time a reasonable estimate for all or a portion of the effects can be made, and provisional amounts can be recognized and adjusted as information becomes available, prepared, or analyzed. The Company calculated its best estimate of the impact of the Act in its December 31, 2017 income tax provision in accordance with its understanding of the Act and guidance available as of the date of the filing of the Annual Report on Form 10-K and as a result recorded a provisional income tax benefit of $84.8 million in the fourth quarter of 2017, the period in which the legislation was enacted. The provisional amount related to the remeasurement of certain deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future was a decrease to income tax expense of $147.7 million. The remeasurement of deferred taxes requires further analysis regarding the state tax impacts of the remeasurement, the impact of the Act on the taxation of executive compensation arrangements, changes to tax capitalization provisions and other aspects of the Act that may impact our tax balances. The amount related to the one-time transition tax on the mandatory deemed repatriation of foreign earnings was an increase to income tax expense of $62.9 million. The determination of the transition tax requires additional analysis regarding the amount and composition of the Company’s historical foreign earnings and foreign tax credit position. We have not made any additional measurement-period adjustments related to these items during the quarter. However, we are continuing to gather additional information to complete our accounting for these items and expect to complete the analysis required to complete our accounting within the prescribed measurement period.

Income Taxes

We manage our affairs so that we are centrally managed and controlled in the U.K. and therefore have our tax residency in the U.K. The provision for income taxes consists of provisions for U.K. and international income taxes. We operate in an international environment with operations in various locations outside the U.K. Accordingly, the consolidated income tax rate is a composite rate reflecting the earnings in the various locations and the applicable rates.

The effective income tax rate for the three months ended March 31, 2018 was 20.9%, compared to 22.1% for 2017. We continue to actively pursue initiatives to reduce our effective tax rate. The tax rate in any quarter can be affected positively or negatively by adjustments that are required to be reported in the specific quarter of resolution. The liability for uncertain tax positions was $35.3 million and $36.6 million at March 31, 2018 and December 31, 2017, respectively. We record penalties and interest related to unrecognized tax benefits in Provision for income taxes and Net interest expense, respectively, on the Condensed Consolidated Statements of Operations and Comprehensive Income, which is consistent with our past practices.

U.S. tax reform

On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the “Act”) was signed into law making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a corporate tax rate decrease from 35% to 21% effective for tax years beginning after December 31, 2017, the transition of U.S. international taxation from a worldwide tax system to a territorial system, and a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings as of December 31, 2017.

Given the significance of the Act, Staff Accounting Bulletin No. 118 ("SAB 118") was issued to address the application of GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Act. SAB 118 allows registrants to record provisional amounts during a one year “measurement period.” The measurement period is deemed to have ended when the registrant has obtained, prepared, and analyzed the information necessary to finalize its accounting. During the measurement period, impacts of the law are expected to be recorded at the time a reasonable estimate for all or a portion of the effects can be made, and provisional amounts can be recognized and adjusted as information becomes available, prepared, or analyzed.

The Company calculated its best estimate of the impact of the Act in its December 31, 2017 income tax provision in accordance with its understanding of the Act and guidance available as of the date of the filing of the Annual Report on Form 10-K and as a result recorded a provisional income tax benefit of $84.8 million in the fourth quarter of 2017, the period in which the legislation was enacted. The provisional amount related to the remeasurement of certain deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future was a decrease to income tax expense of $147.7 million. The remeasurement of deferred taxes requires further analysis regarding the state tax impacts of the remeasurement, the impact of the Act on the taxation of executive compensation arrangements, changes to tax capitalization provisions and other aspects of the Act that may impact our tax balances.

The amount related to the one-time transition tax on the mandatory deemed repatriation of foreign earnings was an increase to income tax expense of $62.9 million. The determination of the transition tax requires additional analysis regarding the amount and composition of the Company’s historical foreign earnings and foreign tax credit position.

We have not made any additional measurement-period adjustments related to these items during the quarter. However, we are continuing to gather additional information to complete our accounting for these items and expect to complete the analysis required to complete our accounting within the prescribed measurement period.