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Accelerating Aon United Program - Restructuring Liabilities for the Program (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2024 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Restructuring Reserve [Roll Forward] |  |  |  |
Charges |  | $ 389 | $ 135 | $ 0
Operating lease ROU asset expense |  | 186 | 141 |
Accelerating Aon United Program |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Liability balance as of January 1, 2024 |  | 100 |  |
Charges |  | 389 | 135 |
Cash payments |  | (268) |  |
Foreign currency translation and other |  | (3) |  |
Non-cash charges |  | (104) |  |
Liability balance as of December 31, 2024 | $ 114 | 114 | 100 |
Total costs incurred from inception to date | 524 | 524 |  |
Operating lease ROU asset expense | 27 |  |  |
Accelerating Aon United Program | Technology and other |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Liability balance as of January 1, 2024 |  | 14 |  |
Charges |  | 126 |  |
Cash payments |  | (96) |  |
Foreign currency translation and other |  | 0 |  |
Non-cash charges |  | (27) |  |
Liability balance as of December 31, 2024 | 17 | 17 | 14 |
Total costs incurred from inception to date | 140 | 140 |  |
Accelerating Aon United Program | Workforce optimization |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Liability balance as of January 1, 2024 |  | 86 |  |
Charges |  | 197 |  |
Cash payments |  | (172) |  |
Foreign currency translation and other |  | (3) |  |
Non-cash charges |  | (11) |  |
Liability balance as of December 31, 2024 | 97 | 97 | 86 |
Total costs incurred from inception to date | 300 | 300 |  |
Accelerating Aon United Program | Asset impairments |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |
Liability balance as of January 1, 2024 |  | 0 |  |
Charges |  | 66 |  |
Cash payments |  | 0 |  |
Foreign currency translation and other |  | 0 |  |
Non-cash charges |  | (66) |  |
Liability balance as of December 31, 2024 | 0 | 0 | $ 0 |
Total costs incurred from inception to date | $ 84 | $ 84 |  |

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- Definition Amount of periodic reduction over lease term of carrying amount of right-of-use asset from operating lease. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-28 + Details
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- Definition Amount of cash payments made as the result of exit or disposal activities. Excludes payments associated with a discontinued operation or an asset retirement obligation. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482017/420-10-50-1 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 17 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-17 + Details
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- Definition Amount of costs incurred to date for the specified restructuring cost. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4.d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479823/420-10-S99-2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4.b.1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479823/420-10-S99-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482017/420-10-50-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482017/420-10-50-1 + Details
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