Principles of Consolidation and Other Matters (Policies)	6 Months Ended
Jun. 30, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and Cash Equivalents	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 primarily related to regulatory requirements outside of the U.S., or as collateral under captive insurance arrangements.
Allowance for Credit Losses on Accounts Receivable	Allowance for Credit Losses on Accounts Receivable The Company’s policy for providing an allowance for credit losses on its accounts receivable is based on a combination of factors, including historical write-offs, aging of balances, and other qualitative and quantitative analyses.
Investments	Investments The caption "Investment income" in the consolidated statements of income comprises of 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 investments in certain private equity funds. Investments in private equity funds are accounted for in accordance with 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 its proportionate share of the change in fair value of the funds are recorded in earnings. Investments accounted for in accordance with the equity method of accounting are included in other assets in the consolidated balance sheets.
Income Taxes	Income Taxes The Company's effective tax rate for the three months ended June 30, 2025 was 25.2%, compared with 27.1% for the corresponding period of 2024. The effective tax rates for the six months ended June 30, 2025 and 2024 were 23.9% and 25.4%, respectively. The tax rate in each period reflects the impact of discrete tax items such as excess tax benefits related to share-based compensation, enacted tax legislation, changes in uncertain tax positions, deferred tax adjustments, non-taxable adjustments related to contingent consideration for acquisitions, and valuation allowances for certain tax credits and attributes. The excess tax benefit related to share-based payments is the most significant discrete item in both periods, reducing the effective tax rate by 0.2% and 0.7% for the three months ended June 30, 2025 and 2024, respectively, and by 1.2% and 1.6% for the six months ended June 30, 2025 and 2024, respectively. The Company's tax rate reflects its income, statutory tax rates, and tax planning in the various jurisdictions in which it operates. Significant judgment is required in determining the annual effective tax rate and in evaluating uncertain tax positions. Losses in one jurisdiction generally cannot offset earnings in another, and within certain jurisdictions profits and losses may not offset between entities. Consequently, losses in certain jurisdictions may require valuation allowances affecting the effective tax rate, depending on estimates of the realizability of associated deferred tax assets. The tax rate is also sensitive to changes in unrecognized tax benefits, including the impact of settled tax audits and expired statutes of limitations. 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 were $114 million at June 30, 2025, and $112 million at December 31, 2024. It is reasonably possible that the total amount of unrecognized tax benefits could decrease up to approximately $69 million within the next twelve months due to settlement of audits and expirations of statutes of limitations. In 2024, the Company received closure notices and assessments from the U.K. tax authority in relation to its 2016-2020 examinations which disallowed certain interest expense deductions. The Company has appealed the assessments and resolving this matter through litigation or alternative dispute resolution may take several years. The Company believes the resolution of tax matters will not have a material effect on the consolidated financial position of the Company. However, an adverse resolution of tax matters could have a material impact on the Company's net income or cash flows and on its effective tax rate in a particular future period. Changes in tax laws, rulings, policies, or related legal and regulatory interpretations occur frequently and may have significant favorable or adverse impacts on our effective tax rate. On July 4, 2025, new U.S tax legislation was signed into law (known as the "One Big Beautiful Bill Act" or "OBBBA") which makes permanent many of the tax provisions enacted in 2017 as part of the Tax Cuts and Jobs Act that were set to expire at the end of 2025. In addition, the OBBBA makes changes to certain U.S. corporate tax provisions, but many are generally not effective until 2026. The Company is currently evaluating the impact of the new legislation but does not expect it to have a material impact on the results of operations. In 2021, the Organization for Economic Cooperation and Development ("OECD") released model rules for a 15% global minimum tax, known as Pillar Two. Pillar Two has now been enacted by most key non-U.S. jurisdictions where the Company operates, including the U.K. and Ireland. Parts of the minimum tax rules were applicable in 2024, with the remaining provisions becoming fully effective for 2025. This minimum tax is treated as a period cost and does not have a material impact on the Company's financial results from operations for the current period. The Company continues to monitor legislative developments, as well as additional guidance from countries that have enacted Pillar Two legislation, and will ensure it complies with any changes.
Restructuring Costs	Restructuring Costs Charges associated with restructuring activities are recognized in accordance with applicable accounting guidance which includes accounting for disposal or exit activities, guidance related to impairment of right-of-use ("ROU") assets related to real estate leases, as well as other costs resulting from accelerated depreciation or amortization of leasehold improvements and other property and equipment. Severance and related costs are recognized based on amounts due under established severance plans or estimates of one-time benefits that will be provided. Typically, severance benefits are recognized when the impacted colleagues are notified of their expected termination and such termination is expected to occur within the legally required notification period. These costs are included in compensation and benefits in the consolidated statements of income. Costs for real estate consolidation are recognized based on the type of cost, and the expected future use of the facility. For locations where the Company does not expect to sub-lease the property, the amortization of any ROU asset is accelerated from the decision date to the cease use date. For locations where the Company expects to sub-lease the properties subsequent to its vacating the property, the ROU asset is reviewed for potential impairment at the earlier of the cease use date or the date a sub-lease is signed. To determine the amount of impairment, the fair value of the ROU asset is determined based on the present value of the estimated net cash flows related to the property. Contractual costs outside of the ROU asset are recognized based on the net present value of expected future cash outflows for which the Company will not receive any benefit. Such amounts are reliant on estimates of future sub-lease income to be received and future contractual costs to be incurred. These costs are included in other operating expenses in the consolidated statements of income. Other costs related to restructuring, such as moving, legal or consulting costs are recognized as incurred. These costs are included in other operating expenses in the consolidated statements of income.
Foreign Currency	Foreign Currency The financial statements of our international subsidiaries are translated from functional currency to U.S. dollars using month-end exchange rates for assets and liabilities, and average monthly exchange rates during the period for revenues and expenses. Translation adjustments are recorded in accumulated other comprehensive income (loss) ("AOCI") within the consolidated statements of equity. Foreign exchange transaction gains and losses resulting from the conversion of the transaction currency to functional currency are included in operating income in the consolidated statements of income.
Revenue	Revenue The core principle of the revenue recognition guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve this principle, the entity applies the following steps: identify the contract(s) with the customer, identify the performance obligations in the contract(s), determine the transaction price, allocate the transaction price to the performance obligations in the contract, and recognize revenue when (or as) the entity satisfies a performance obligation. In accordance with the accounting guidance, a performance obligation is satisfied either at a "point in time" or "over time", depending on the nature of the product or service provided, and the specific terms of the contract with customers. Other revenue included in the consolidated statements of income that is not from contracts with customers is less than 1% of total revenue and is not presented as a separate line item.
Fair Value Measurements	Fair Value Measurements Fair Value Hierarchy The Company has categorized its assets and liabilities that are valued at fair value on a recurring basis into a three-level fair value hierarchy. The fair value hierarchy gives the highest priority to quoted prices in active markets for identical assets and liabilities (Level 1) and lowest priority to unobservable inputs (Level 3). In some cases, the inputs used to measure fair value might fall into different levels of the fair value hierarchy. In such cases, the level in the fair value hierarchy, for disclosure purposes, is determined based on the lowest level input that is significant to the fair value measurement. Assets and liabilities recorded in the consolidated balance sheets at fair value are categorized based on the inputs in the valuation techniques as follows: Level 1.Assets and liabilities whose values are based on unadjusted quoted prices for identical assets or liabilities in an active market (examples include active exchange-traded equity securities and exchange-traded money market mutual funds). Assets and liabilities measured using Level 1 inputs include exchange-traded equity securities, exchange-traded mutual funds and money market funds. Level 2.Assets and liabilities whose values are based on the following: a)quoted prices for similar assets or liabilities in active markets; b)quoted prices for identical or similar assets or liabilities in non-active markets (examples include corporate and municipal bonds, which trade infrequently); c)pricing models whose inputs are observable for substantially the full term of the asset or liability (examples include most over-the-counter derivatives, including interest rate and currency swaps); and d)pricing models whose inputs are derived principally from or corroborated by observable market data through correlation or other means for substantially the full asset or liability (for example, certain mortgage loans). Level 3.Assets and liabilities whose values are based on prices, or valuation techniques that require inputs that are both unobservable and significant to the overall fair value measurement. These inputs reflect management’s own assumptions about the assumptions a market participant would use in pricing the asset or liability. Assets and liabilities measured using Level 3 inputs relate to assets and liabilities for contingent purchase consideration. Valuation Techniques Equity Securities, Money Market Funds and Mutual Funds – Level 1 Investments for which market quotations are readily available are valued at the sale price on their principal exchange or, for certain markets, official closing bid price. Money market funds are valued at a readily determinable price. Contingent Purchase Consideration Assets and Liabilities – Level 3 Purchase consideration for some acquisitions and dispositions made by the Company includes contingent consideration arrangements. Contingent consideration arrangements are based primarily on EBITDA or revenue targets over a period of 2 to 4 years. The fair value of the contingent purchase consideration asset and liability is estimated as the present value of future cash flows to be paid, based on projections of revenue and earnings and related targets of the acquired and disposed entities.
Recently Issued Accounting Pronouncements Not Yet Adopted and New Accounting Pronouncement Adopted Effective December 31, 2024	Recently Issued Accounting Pronouncements Not Yet Adopted: In November 2024, the FASB issued an accounting standard update on the disaggregated disclosure of income statement expenses. The new guidance requires disclosures about specific types of expenses included in the expense captions presented on the face of the income statement, as well as disclosures about selling expenses. The new standard does not change the requirements for the presentation of expenses on the face of the income statement. The standard is effective for fiscal years beginning after December 15, 2026, and interim periods within fiscal years beginning after December 15, 2027. Early adoption is permitted. The new guidance will be applied prospectively with the option for retrospective application. The Company is currently evaluating the guidance and expects it to only impact disclosures with no impact to results of operations, cash flows, or financial condition. In December 2023, the FASB issued an accounting standard update on income tax disclosures, primarily related to the rate reconciliation and income taxes paid information. The new guidance requires that public business entities, on an annual basis, disclose specific categories in the rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. In addition, all entities are required to disclose on an annual basis the amount of income taxes paid, net of refunds received, disaggregated by federal, state and foreign taxes, and by individual jurisdictions if the amount is equal to or greater than 5% of total income taxes paid, net of refunds received. The guidance is effective for annual periods beginning after December 15, 2024. Early adoption is permitted. An entity should apply the amendments in the standard prospectively, even though retrospective application is permitted. The Company is currently evaluating the guidance and expects it to only impact disclosures with no impact to results of operations, cash flows, or financial condition. New Accounting Pronouncement Adopted Effective December 31, 2024: In November 2023, the FASB issued an accounting standard update on segment reporting. The new guidance: (1) introduces a requirement to disclose significant segment expenses regularly provided to the CODM, (2) extends certain annual disclosures to interim periods, (3) clarifies disclosure requirements for single reportable segment entities, (4) permits more than one measure of segment profit or loss to be reported under certain conditions, and (5) requires disclosure of the title and position of the CODM. The standard was effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Early adoption was permitted. The guidance applies retrospectively to all periods presented in the financial statements. The Company adopted the new standard effective December 31, 2024, which impacted disclosures only, with no impact to results of operations, cash flows, or financial condition.

Principles of Consolidation and Other Matters (Policies)

6 Months Ended

Jun. 30, 2025

Organization, Consolidation and Presentation of Financial Statements [Abstract]

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 primarily related to regulatory requirements outside of the U.S., or as collateral under captive insurance arrangements.

Allowance for Credit Losses on Accounts Receivable

The Company’s policy for providing an allowance for credit losses on its accounts receivable is based on a combination of factors, including historical write-offs, aging of balances, and other qualitative and quantitative analyses.

Investments

The caption "Investment income" in the consolidated statements of income comprises of 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 investments in certain private equity funds. Investments in private equity funds are accounted for in accordance with 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 its proportionate share of the change in fair value of the funds are recorded in earnings. Investments accounted for in accordance with the equity method of accounting are included in other assets in the consolidated balance sheets.

Income Taxes

The Company's effective tax rate for the three months ended June 30, 2025 was 25.2%, compared with 27.1% for the corresponding period of 2024. The effective tax rates for the six months ended June 30, 2025 and 2024 were 23.9% and 25.4%, respectively.

The tax rate in each period reflects the impact of discrete tax items such as excess tax benefits related to share-based compensation, enacted tax legislation, changes in uncertain tax positions, deferred tax adjustments, non-taxable adjustments related to contingent consideration for acquisitions, and valuation allowances for certain tax credits and attributes.

The excess tax benefit related to share-based payments is the most significant discrete item in both periods, reducing the effective tax rate by 0.2% and 0.7% for the three months ended June 30, 2025 and 2024, respectively, and by 1.2% and 1.6% for the six months ended June 30, 2025 and 2024, respectively.

The Company's tax rate reflects its income, statutory tax rates, and tax planning in the various jurisdictions in which it operates. Significant judgment is required in determining the annual effective tax rate and in evaluating uncertain tax positions. Losses in one jurisdiction generally cannot offset earnings in another, and within certain jurisdictions profits and losses may not offset between entities. Consequently, losses in certain jurisdictions may require valuation allowances affecting the effective tax rate, depending on estimates of the realizability of associated deferred tax assets. The tax rate is also sensitive to changes in unrecognized tax benefits, including the impact of settled tax audits and expired statutes of limitations.

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 were $114 million at June 30, 2025, and $112 million at December 31, 2024. It is reasonably possible that the total amount of unrecognized tax benefits could decrease up to approximately $69 million within the next twelve months due to settlement of audits and expirations of statutes of limitations.

In 2024, the Company received closure notices and assessments from the U.K. tax authority in relation to its 2016-2020 examinations which disallowed certain interest expense deductions. The Company has appealed the assessments and resolving this matter through litigation or alternative dispute resolution may take several years. The Company believes the resolution of tax matters will not have a material effect on the consolidated financial position of the Company. However, an adverse resolution of tax matters could have a material impact on the Company's net income or cash flows and on its effective tax rate in a particular future period.

Changes in tax laws, rulings, policies, or related legal and regulatory interpretations occur frequently and may have significant favorable or adverse impacts on our effective tax rate.

On July 4, 2025, new U.S tax legislation was signed into law (known as the "One Big Beautiful Bill Act" or "OBBBA") which makes permanent many of the tax provisions enacted in 2017 as part of the Tax Cuts and Jobs Act that were set to expire at the end of 2025. In addition, the OBBBA makes changes to certain U.S. corporate tax provisions, but many are generally not effective until 2026. The Company is currently evaluating the impact of the new legislation but does not expect it to have a material impact on the results of operations.

In 2021, the Organization for Economic Cooperation and Development ("OECD") released model rules for a 15% global minimum tax, known as Pillar Two. Pillar Two has now been enacted by most key non-U.S. jurisdictions where the Company operates, including the U.K. and Ireland. Parts of the minimum tax rules were applicable in 2024, with the remaining provisions becoming fully effective for 2025. This minimum tax is treated as a period cost and does not have a material impact on the Company's financial results from operations for the current period.

The Company continues to monitor legislative developments, as well as additional guidance from countries that have enacted Pillar Two legislation, and will ensure it complies with any changes.

Restructuring Costs

Charges associated with restructuring activities are recognized in accordance with applicable accounting guidance which includes accounting for disposal or exit activities, guidance related to impairment of right-of-use ("ROU") assets related to real estate leases, as well as other costs resulting from accelerated depreciation or amortization of leasehold improvements and other property and equipment.

Severance and related costs are recognized based on amounts due under established severance plans or estimates of one-time benefits that will be provided. Typically, severance benefits are recognized when the impacted colleagues are notified of their expected termination and such termination is expected to occur within the legally required notification period. These costs are included in compensation and benefits in the consolidated statements of income.

Costs for real estate consolidation are recognized based on the type of cost, and the expected future use of the facility. For locations where the Company does not expect to sub-lease the property, the amortization of any ROU asset is accelerated from the decision date to the cease use date. For locations where the Company expects to sub-lease the properties subsequent to its vacating the property, the ROU asset is reviewed for potential impairment at the earlier of the cease use date or the date a sub-lease is signed. To determine the amount of impairment, the fair value of the ROU asset is determined based on the present value of the estimated net cash flows related to the property. Contractual costs outside of the ROU asset are recognized based on the net present value of expected future cash outflows for which the Company will not receive any benefit. Such amounts are reliant on estimates of future sub-lease income to be received and future contractual costs to be incurred. These costs are included in other operating expenses in the consolidated statements of income.

Other costs related to restructuring, such as moving, legal or consulting costs are recognized as incurred. These costs are included in other operating expenses in the consolidated statements of income.

Foreign Currency

The financial statements of our international subsidiaries are translated from functional currency to U.S. dollars using month-end exchange rates for assets and liabilities, and average monthly exchange rates during the period for revenues and expenses. Translation adjustments are recorded in accumulated other comprehensive income (loss) ("AOCI") within the consolidated statements of equity. Foreign exchange transaction gains and losses resulting from the conversion of the transaction currency to functional currency are included in operating income in the consolidated statements of income.

Revenue

The core principle of the revenue recognition guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services.

To achieve this principle, the entity applies the following steps: identify the contract(s) with the customer, identify the performance obligations in the contract(s), determine the transaction price, allocate the transaction price to the performance obligations in the contract, and recognize revenue when (or as) the entity satisfies a performance obligation. In accordance with the accounting guidance, a performance obligation is satisfied either at a "point in time" or "over time", depending on the nature of the product or service provided, and the specific terms of the contract with customers.

Other revenue included in the consolidated statements of income that is not from contracts with customers is less than 1% of total revenue and is not presented as a separate line item.

Fair Value Measurements

Fair Value Hierarchy

The Company has categorized its assets and liabilities that are valued at fair value on a recurring basis into a three-level fair value hierarchy. The fair value hierarchy gives the highest priority to quoted prices in active markets for identical assets and liabilities (Level 1) and lowest priority to unobservable inputs (Level 3). In some cases, the inputs used to measure fair value might fall into different levels of the fair value hierarchy. In such cases, the level in the fair value hierarchy, for disclosure purposes, is determined based on the lowest level input that is significant to the fair value measurement. Assets and liabilities recorded in the consolidated balance sheets at fair value are categorized based on the inputs in the valuation techniques as follows:

Level 1.Assets and liabilities whose values are based on unadjusted quoted prices for identical assets or liabilities in an active market (examples include active exchange-traded equity securities and exchange-traded money market mutual funds).

Assets and liabilities measured using Level 1 inputs include exchange-traded equity securities, exchange-traded mutual funds and money market funds.

Level 2.Assets and liabilities whose values are based on the following:

a)quoted prices for similar assets or liabilities in active markets;

b)quoted prices for identical or similar assets or liabilities in non-active markets (examples include corporate and municipal bonds, which trade infrequently);

c)pricing models whose inputs are observable for substantially the full term of the asset or liability (examples include most over-the-counter derivatives, including interest rate and currency swaps); and

d)pricing models whose inputs are derived principally from or corroborated by observable market data through correlation or other means for substantially the full asset or liability (for example, certain mortgage loans).

Level 3.Assets and liabilities whose values are based on prices, or valuation techniques that require inputs that are both unobservable and significant to the overall fair value measurement. These inputs reflect management’s own assumptions about the assumptions a market participant would use in pricing the asset or liability.

Assets and liabilities measured using Level 3 inputs relate to assets and liabilities for contingent purchase consideration.

Valuation Techniques

Equity Securities, Money Market Funds and Mutual Funds – Level 1

Investments for which market quotations are readily available are valued at the sale price on their principal exchange or, for certain markets, official closing bid price. Money market funds are valued at a readily determinable price.

Contingent Purchase Consideration Assets and Liabilities – Level 3

Purchase consideration for some acquisitions and dispositions made by the Company includes contingent consideration arrangements. Contingent consideration arrangements are based primarily on EBITDA or revenue targets over a period of 2 to 4 years. The fair value of the contingent purchase consideration asset and liability is estimated as the present value of future cash flows to be paid, based on projections of revenue and earnings and related targets of the acquired and disposed entities.

Recently Issued Accounting Pronouncements Not Yet Adopted and New Accounting Pronouncement Adopted Effective December 31, 2024

Recently Issued Accounting Pronouncements Not Yet Adopted:

In November 2024, the FASB issued an accounting standard update on the disaggregated disclosure of income statement expenses. The new guidance requires disclosures about specific types of expenses included in the expense captions presented on the face of the income statement, as well as disclosures about selling expenses. The new standard does not change the requirements for the presentation of expenses on the face of the income statement. The standard is effective for fiscal years beginning after December 15, 2026, and interim periods within fiscal years beginning after December 15, 2027. Early adoption is permitted. The new guidance will be applied prospectively with the option for retrospective application. The Company is currently evaluating the guidance and expects it to only impact disclosures with no impact to results of operations, cash flows, or financial condition.

In December 2023, the FASB issued an accounting standard update on income tax disclosures, primarily related to the rate reconciliation and income taxes paid information. The new guidance requires that public business entities, on an annual basis, disclose specific categories in the rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. In addition, all entities are required to disclose on an annual basis the amount of income taxes paid, net of refunds received, disaggregated by federal, state and foreign taxes, and by individual jurisdictions if the amount is equal to or greater than 5% of total income taxes paid, net of refunds received. The guidance is effective for annual periods beginning after December 15, 2024. Early adoption is permitted. An entity should apply the amendments in the standard prospectively, even though retrospective application is permitted. The Company is currently evaluating the guidance and expects it to only impact disclosures with no impact to results of operations, cash flows, or financial condition.

New Accounting Pronouncement Adopted Effective December 31, 2024:

In November 2023, the FASB issued an accounting standard update on segment reporting. The new guidance: (1) introduces a requirement to disclose significant segment expenses regularly provided to the CODM, (2) extends certain annual disclosures to interim periods, (3) clarifies disclosure requirements for single reportable segment entities, (4) permits more than one measure of segment profit or loss to be reported under certain conditions, and (5) requires disclosure of the title and position of the CODM. The standard was effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Early adoption was permitted. The guidance applies retrospectively to all periods presented in the financial statements. The Company adopted the new standard effective December 31, 2024, which impacted disclosures only, with no impact to results of operations, cash flows, or financial condition.