Principles of Consolidation and Other Matters	9 Months Ended
Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Principles of Consolidation and Other Matters	Principles of Consolidation and Other Matters The consolidated financial statements included herein have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission. While certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America have been omitted pursuant to such rules and regulations for interim filings, the Company believes that the information and disclosures presented are adequate to make such information and disclosures not misleading. These consolidated financial statements should be read in conjunction with the consolidated financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 (the "2017 Form 10-K"). The financial information contained herein reflects all normal recurring adjustments which are, in the opinion of management, necessary for a fair presentation of the Company’s consolidated financial statements as of and for the three and nine month periods ended September 30, 2018 and 2017. Cash and Cash Equivalents Cash and cash equivalents primarily consist of certificates of deposit and time deposits, with original maturities of three months or less, and money market funds. The estimated fair value of the Company's cash and cash equivalents approximates their carrying value. The Company is required to maintain operating funds of approximately $189 million, primarily related to regulatory requirements outside the United States or as collateral under captive insurance arrangements. Investments The caption "Investment income (loss)" in the consolidated statements of income comprises realized and unrealized gains and losses from investments recognized in earnings. It includes, when applicable, other than temporary declines in the value of securities, mark-to-market increases or decreases in equity investments with readily determinable fair values and equity method gains or losses on the Company's investments in private equity funds. The Company holds certain equity investments, that under legacy GAAP, were previously accounted as available for sale securities, whereby the mark-to-market change was recorded to other comprehensive income in its consolidated balance sheet. As discussed in Note 18, effective January 1, 2018, the Company adopted new accounting guidance that requires equity investments (except those accounted for under the equity method of accounting, or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. The Company recorded a cumulative-effect adjustment that increased retained earnings as of the beginning of the period of adoption by $14 million, reflecting the reclassification of cumulative unrealized gains, net of tax as of December 31, 2017 from accumulated other comprehensive income to retained earnings. Prior periods have not been restated. The Company holds investments in certain private equity funds that are accounted for under the equity method of accounting using a consistently applied three-month lag period adjusted for any known significant changes from the lag period to the reporting date of the Company. The underlying private equity funds follow investment company accounting, where investments within the fund are carried at fair value. Investment gains or losses for the Company's proportionate share of the change in fair value of the funds are recorded in earnings. Investments accounted for using the equity method of accounting are included in "other assets" in the consolidated balance sheets. The Company recorded net investment losses of $52 million and $24 million for the three and nine month periods ended September 30, 2018, respectively, and a net investment loss of $2 million and a net investment gain of $3 million for the three and nine month periods ended September 30, 2017, respectively. The three month and nine month periods ended September 30, 2018 include an $81 million charge related to an other than temporary decline in the Company's equity method investment in Alexander Forbes (see Note 10). The three month period ending September 30, 2018 also includes gains of $25 million related to mark-to-market changes in equity securities and gains of $4 million related to investments in private equity funds. The nine months ended September 30, 2018 also includes gains of $43 million related to mark-to-market changes in equity securities and $14 million related to investments in private equity funds and other investments. Income Taxes The Company's effective tax rate in the third quarter of 2018 was 27.5% compared with 26.2% in the third quarter of 2017. The effective tax rates for the first nine months of 2018 and 2017 were 25.2% and 25.9%, respectively. The rate in the first nine months of 2018 reflects ongoing impacts of the Tax Cuts and Jobs Act (the "TCJA"), primarily the reduced 21% U.S. statutory rate and certain tax planning benefits, largely offset by higher estimated costs from a new method of taxing non-U.S. based operations, greater disallowance of compensation and entertainment deductions, as well as the effect of a charge related to the Company’s investment in Alexander Forbes as discussed in Note 10 and a reduction in excess tax benefits related to share compensation. The rate in the third quarter of 2017 reflects foreign operations taxed at rates below the 35% U.S. statutory tax rate, including the effect of repatriation. The tax rates in both periods reflect the impact of discrete tax matters, tax legislation and nontaxable adjustments to contingent acquisition consideration. As a result of TCJA, two discrete provisional charges were recorded in the fourth quarter of 2017. The transition to the new method of taxing non-U.S. based operations resulted in a transition tax payable over eight years on undistributed earnings of non-U.S. subsidiaries. This mandatory taxation of accumulated foreign earnings substantially changed the economic considerations of continued permanent investment of those accumulated earnings, a key component of the Company's global capital strategy. As a result of the transition tax, the Company anticipates repatriating the majority of the accumulated earnings that it previously intended to permanently invest. A charge of $240 million was recorded in the fourth quarter of 2017 as a provisional estimate of the transition tax and ancillary effects. The provisional estimate of transition tax includes state taxes and foreign withholding taxes related to the change in the Company's indefinite reinvestment assertion with respect to the Company's pre-2018 foreign earnings. The Company previously considered most unremitted earnings of its non-U.S. subsidiaries, except amounts repatriated in the year earned, to be permanently reinvested and, accordingly, recorded no deferred U.S. income taxes on such earnings. The Company has initially analyzed its global capital requirements and potential tax liabilities attributable to repatriation. The Company estimates that it will repatriate $3.4 billion of pre-2018 earnings that was previously considered indefinitely invested. Included in the $240 million charge is a $53 million provisional estimate for withholding and state income taxes. The Company has revised the provisional estimate in the third quarter of 2018 to $226 million based on the analysis of the available information and taking into consideration the subsequent guidance issued regarding the legislation. Further revisions to the transition tax provisional estimate, which includes estimated state and withholding tax, may occur as pending guidance regarding the legislation is finalized and the analysis of same is completed. In addition, reducing the U.S. corporate tax rate from 35% to 21% and the change in deductibility of certain compensation awards to certain executive officers of the Company effective on January 1, 2018, resulted in a net charge of $220 million in the fourth quarter of 2017 to reduce the value of the U.S. deferred tax assets and liabilities. Adjustments during the first nine months of 2018 to provisional estimates of transition taxes and to U.S. deferred tax assets and liabilities, have decreased income tax expense by $14 million and increased income tax expense by $3 million, respectively. In December of 2017, the SEC issued Staff Accounting Bulletin 118 ("SAB 118"), establishing a one-year measurement period to complete the accounting for the income tax effects of the TCJA. SAB 118 anticipates three alternative states of completion at the end of the reporting period of accounting for these effects: (1) the tax accounting work has been completed with respect to an item; (2) a provisional amount has been recognized because a reasonable estimate was possible, or (3) a reasonable estimate cannot be provided. The Company believes its analysis of the TCJA to date provides an appropriate basis to record a provisional estimate. The provisional estimates include the effects of the deemed repatriation tax and the Company's position with respect to permanently reinvested earnings and the remeasurement of U.S. deferred taxes based on estimated enactment-date deferred tax balances, which have been adjusted in 2018 as the 2017 tax returns are filed and may be further adjusted as additional guidance is issued. TCJA’s transition tax requires detailed calculations of current and accumulated taxable earnings at the level of each foreign subsidiary, computed in functional currency at the greater of two alternative measurement dates and converted into U.S. dollars. In preparing its 2017 U.S. federal return the Company performed these calculations for approximately seven hundred foreign subsidiaries. In the third quarter, management updated its estimate of the transition tax, its global permanent investment strategy, and finalized the impact on U.S. deferred tax assets from the change in tax rate. However, given the significant complexity of the TCJA and still-anticipated guidance from the U.S. Treasury and State and Local tax authorities on its implementation, estimates regarding the transition tax and the Company’s global permanent investment strategy may be further adjusted during the fourth quarter. The Company is routinely examined by tax authorities in the jurisdictions in which it has significant operations. The Company regularly considers the likelihood of assessments in each of the taxing jurisdictions resulting from examinations. When evaluating the potential imposition of penalties, the Company considers a number of relevant factors under penalty statutes, including appropriate disclosure of the tax return position, the existence of legal authority supporting the Company's position, and reliance on the opinion of professional tax advisors. The Company reports a liability for unrecognized tax benefits resulting from uncertain tax positions taken or expected to be taken in tax returns. The Company's gross unrecognized tax benefits increased from $71 million at December 31, 2017 to $72 million at September 30, 2018 due to current accruals partially offset by settlements of audits and expirations of statutes of limitation. It is reasonably possible that the total amount of unrecognized tax benefits will decrease between zero and approximately $9 million within the next twelve months due to settlements of audits and expirations of statutes of limitation.

Principles of Consolidation and Other Matters

The consolidated financial statements included herein have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission. While certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America have been omitted pursuant to such rules and regulations for interim filings, the Company believes that the information and disclosures presented are adequate to make such information and disclosures not misleading. These consolidated financial statements should be read in conjunction with the consolidated financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 (the "2017 Form 10-K").

The financial information contained herein reflects all normal recurring adjustments which are, in the opinion of management, necessary for a fair presentation of the Company’s consolidated financial statements as of and for the three and nine month periods ended September 30, 2018 and 2017.

Cash and Cash Equivalents

Cash and cash equivalents primarily consist of certificates of deposit and time deposits, with original maturities of three months or less, and money market funds. The estimated fair value of the Company's cash and cash equivalents approximates their carrying value. The Company is required to maintain operating funds of approximately $189 million, primarily related to regulatory requirements outside the United States or as collateral under captive insurance arrangements.

Investments

The caption "Investment income (loss)" in the consolidated statements of income comprises realized and unrealized gains and losses from investments recognized in earnings. It includes, when applicable, other than temporary declines in the value of securities, mark-to-market increases or decreases in equity investments with readily determinable fair values and equity method gains or losses on the Company's investments in private equity funds.

The Company holds certain equity investments, that under legacy GAAP, were previously accounted as available for sale securities, whereby the mark-to-market change was recorded to other comprehensive income in its consolidated balance sheet. As discussed in Note 18, effective January 1, 2018, the Company adopted new accounting guidance that requires equity investments (except those accounted for under the equity method of accounting, or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. The Company recorded a cumulative-effect adjustment that increased retained earnings as of the beginning of the period of adoption by $14 million, reflecting the reclassification of cumulative unrealized gains, net of tax as of December 31, 2017 from accumulated other comprehensive income to retained earnings. Prior periods have not been restated.

The Company holds investments in certain private equity funds that are accounted for under the equity method of accounting using a consistently applied three-month lag period adjusted for any known significant changes from the lag period to the reporting date of the Company. The underlying private equity funds follow investment company accounting, where investments within the fund are carried at fair value. Investment gains or losses for the Company's proportionate share of the change in fair value of the funds are recorded in earnings. Investments accounted for using the equity method of accounting are included in "other assets" in the consolidated balance sheets.

The Company recorded net investment losses of $52 million and $24 million for the three and nine month periods ended September 30, 2018, respectively, and a net investment loss of $2 million and a net investment gain of $3 million for the three and nine month periods ended September 30, 2017, respectively. The three month and nine month periods ended September 30, 2018 include an $81 million charge related to an other than temporary decline in the Company's equity method investment in Alexander Forbes (see Note 10). The three month period ending September 30, 2018 also includes gains of $25 million related to mark-to-market changes in equity securities and gains of $4 million related to investments in private equity funds. The nine months ended September 30, 2018 also includes gains of $43 million related to mark-to-market changes in equity securities and $14 million related to investments in private equity funds and other investments.

Income Taxes

The Company's effective tax rate in the third quarter of 2018 was 27.5% compared with 26.2% in the third quarter of 2017. The effective tax rates for the first nine months of 2018 and 2017 were 25.2% and 25.9%, respectively. The rate in the first nine months of 2018 reflects ongoing impacts of the Tax Cuts and Jobs Act (the "TCJA"), primarily the reduced 21% U.S. statutory rate and certain tax planning benefits, largely offset by higher estimated costs from a new method of taxing non-U.S. based operations, greater disallowance of compensation and entertainment deductions, as well as the effect of a charge related to the Company’s investment in Alexander Forbes as discussed in Note 10 and a reduction in excess tax benefits related to share compensation. The rate in the third quarter of 2017 reflects foreign operations taxed at rates below the 35% U.S. statutory tax rate, including the effect of repatriation. The tax rates in both periods reflect the impact of discrete tax matters, tax legislation and nontaxable adjustments to contingent acquisition consideration.

As a result of TCJA, two discrete provisional charges were recorded in the fourth quarter of 2017. The transition to the new method of taxing non-U.S. based operations resulted in a transition tax payable over eight years on undistributed earnings of non-U.S. subsidiaries. This mandatory taxation of accumulated foreign earnings substantially changed the economic considerations of continued permanent investment of those accumulated earnings, a key component of the Company's global capital strategy. As a result of the transition tax, the Company anticipates repatriating the majority of the accumulated earnings that it previously intended to permanently invest. A charge of $240 million was recorded in the fourth quarter of 2017 as a provisional estimate of the transition tax and ancillary effects.

The provisional estimate of transition tax includes state taxes and foreign withholding taxes related to the change in the Company's indefinite reinvestment assertion with respect to the Company's pre-2018 foreign earnings. The Company previously considered most unremitted earnings of its non-U.S. subsidiaries, except amounts repatriated in the year earned, to be permanently reinvested and, accordingly, recorded no deferred U.S. income taxes on such earnings. The Company has initially analyzed its global capital requirements and potential tax liabilities attributable to repatriation. The Company estimates that it will repatriate $3.4 billion of pre-2018 earnings that was previously considered indefinitely invested. Included in the $240 million charge is a $53 million provisional estimate for withholding and state income taxes. The Company has revised the provisional estimate in the third quarter of 2018 to $226 million based on the analysis of the available information and taking into consideration the subsequent guidance issued regarding the legislation. Further revisions to the transition tax provisional estimate, which includes estimated state and withholding tax, may occur as pending guidance regarding the legislation is finalized and the analysis of same is completed.

In addition, reducing the U.S. corporate tax rate from 35% to 21% and the change in deductibility of certain compensation awards to certain executive officers of the Company effective on January 1, 2018, resulted in a net charge of $220 million in the fourth quarter of 2017 to reduce the value of the U.S. deferred tax assets and liabilities. Adjustments during the first nine months of 2018 to provisional estimates of transition taxes and to U.S. deferred tax assets and liabilities, have decreased income tax expense by $14 million and increased income tax expense by $3 million, respectively.

In December of 2017, the SEC issued Staff Accounting Bulletin 118 ("SAB 118"), establishing a one-year measurement period to complete the accounting for the income tax effects of the TCJA. SAB 118 anticipates three alternative states of completion at the end of the reporting period of accounting for these effects: (1) the tax accounting work has been completed with respect to an item; (2) a provisional amount has been recognized because a reasonable estimate was possible, or (3) a reasonable estimate cannot be provided. The Company believes its analysis of the TCJA to date provides an appropriate basis to record a provisional estimate. The provisional estimates include the effects of the deemed repatriation tax and the Company's position with respect to permanently reinvested earnings and the remeasurement of U.S. deferred taxes based on estimated enactment-date deferred tax balances, which have been adjusted in 2018 as the 2017 tax returns are filed and may be further adjusted as additional guidance is issued. TCJA’s transition tax requires detailed calculations of current and accumulated taxable earnings at the level of each foreign subsidiary, computed in functional currency at the greater of two alternative measurement dates and converted into U.S. dollars. In preparing its 2017 U.S. federal return the Company performed these calculations for approximately seven hundred foreign subsidiaries. In the third quarter, management updated its estimate of the transition tax, its global permanent investment strategy, and finalized the impact on U.S. deferred tax assets from the change in tax rate. However, given the significant complexity of the TCJA and still-anticipated guidance from the U.S. Treasury and State and Local tax authorities on its implementation, estimates regarding the transition tax and the Company’s global permanent investment strategy may be further adjusted during the fourth quarter.

The Company is routinely examined by tax authorities in the jurisdictions in which it has significant operations. The Company regularly considers the likelihood of assessments in each of the taxing jurisdictions resulting from examinations. When evaluating the potential imposition of penalties, the Company considers a number of relevant factors under penalty statutes, including appropriate disclosure of the tax return position, the existence of legal authority supporting the Company's position, and reliance on the opinion of professional tax advisors.

The Company reports a liability for unrecognized tax benefits resulting from uncertain tax positions taken or expected to be taken in tax returns. The Company's gross unrecognized tax benefits increased from $71 million at December 31, 2017 to $72 million at September 30, 2018 due to current accruals partially offset by settlements of audits and expirations of statutes of limitation. It is reasonably possible that the total amount of unrecognized tax benefits will decrease between zero and approximately $9 million within the next twelve months due to settlements of audits and expirations of statutes of limitation.