Accounting Principles and Practices	3 Months Ended
Mar. 31, 2025
Accounting Policies [Abstract]
Accounting Principles and Practices	Accounting Principles and Practices New Accounting Pronouncements Accounting Standards Issued But Not Yet Adopted Improvements to Income Tax Disclosures In December 2023, the FASB issued new accounting guidance under ASC 740, Income Taxes, which requires additional income tax disclosures on an annual basis, including disaggregation of information presented within the reconciliation of the expected tax to the reported tax by specific categories, with certain reconciling items 5% or greater broken out by nature and/or jurisdiction. The new guidance also requires disclosure of income taxes paid, net of refunds, broken out by federal, state/local and foreign, including disclosure of individual jurisdictions when greater than 5% of total net income taxes paid. The new guidance is effective for annual periods beginning the year ended December 31, 2025. The Company is evaluating the transition approach as well as the impact the disclosures will have on the Notes to Consolidated Financial Statements. Disaggregation of Income Statement Expenses In November 2024, the FASB issued new accounting guidance under ASC 220, Income Statement — Reporting Comprehensive Income, which requires more detailed information about certain expenses in commonly presented expense captions including inventory, employee compensation, depreciation, and amortization. The new guidance also requires disclosure of total selling expenses and, on an annual basis, an entity’s definition of selling expenses. The new guidance is effective for Aon for the year ended December 31, 2027, with early adoption permitted. Entities may apply the new guidance on a prospective basis, with the option for retrospective application. Aon is currently evaluating the transition approach and the impact the guidance will have on the Notes to Consolidated Financial Statements. Securities and Exchange Commission Final Rules The Enhancement and Standardization of Climate-Related Disclosures for Investors In March 2024, the SEC adopted final rules to enhance and standardize climate-related disclosures. The final rules would require the Company to provide certain climate-related information in Item 7, Management’s Discussion and Analysis regarding material climate-related risks, activities to mitigate or adapt to such risks, information regarding oversight and management of climate-related risks, information on climate-related targets or goals, and disclosure of Scope 1 and 2 GHG emissions. Additionally, within the Notes to Consolidated Financial Statements, the Company would be required to disclose the financial statement effects of severe weather events and other natural conditions. The final rules are effective for Aon for the year ended December 31, 2025, with the exception of GHG emissions disclosures which are effective for Aon for the year ended December 31, 2026. The final rules have been subject to several legal challenges. On April 4, 2024, the SEC voluntarily stayed the final rules pending judicial review, and on March 27, 2025, the SEC voted to end its legal defense of the final rules, although judicial review remains ongoing. The Company is monitoring the judicial process for resolution of the legal challenges and impacts on the disclosure requirements.

In December 2023, the FASB issued new accounting guidance under ASC 740, Income Taxes, which requires additional income tax disclosures on an annual basis, including disaggregation of information presented within the reconciliation of the expected tax to the reported tax by specific categories, with certain reconciling items 5% or greater broken out by nature and/or jurisdiction. The new guidance also requires disclosure of income taxes paid, net of refunds, broken out by federal, state/local and foreign, including disclosure of individual jurisdictions when greater than 5% of total net income taxes paid. The new guidance is effective for annual periods beginning the year ended December 31, 2025. The Company is evaluating the transition approach as well as the impact the disclosures will have on the Notes to Consolidated Financial Statements.

In November 2024, the FASB issued new accounting guidance under ASC 220, Income Statement — Reporting Comprehensive Income, which requires more detailed information about certain expenses in commonly presented expense captions including inventory, employee compensation, depreciation, and amortization. The new guidance also requires disclosure of total selling expenses and, on an annual basis, an entity’s definition of selling expenses. The new guidance is effective for Aon for the year ended December 31, 2027, with early adoption permitted. Entities may apply the new guidance on a prospective basis, with the option for retrospective application. Aon is currently evaluating the transition approach and the impact the guidance will have on the Notes to Consolidated Financial Statements.

In March 2024, the SEC adopted final rules to enhance and standardize climate-related disclosures. The final rules would require the Company to provide certain climate-related information in Item 7, Management’s Discussion and Analysis

regarding material climate-related risks, activities to mitigate or adapt to such risks, information regarding oversight and management of climate-related risks, information on climate-related targets or goals, and disclosure of Scope 1 and 2 GHG emissions. Additionally, within the Notes to Consolidated Financial Statements, the Company would be required to disclose the financial statement effects of severe weather events and other natural conditions. The final rules are effective for Aon for the year ended December 31, 2025, with the exception of GHG emissions disclosures which are effective for Aon for the year ended December 31, 2026. The final rules have been subject to several legal challenges. On April 4, 2024, the SEC voluntarily stayed the final rules pending judicial review, and on March 27, 2025, the SEC voted to end its legal defense of the final rules, although judicial review remains ongoing. The Company is monitoring the judicial process for resolution of the legal challenges and impacts on the disclosure requirements.