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Restructuring Costs (Restructuring Activity) (Details) - JLT Transaction - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021
Restructuring Reserve [Roll Forward] |  |
Beginning of period | $ 69 | $ 106
Restructuring charges | 427 | 163
Cash payments | (193) | (178)
Non-cash charges | (157) | (22)
End of period | 146 | 69
Severance |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 35 | 52
Restructuring charges | 111 | 38
Cash payments | (58) | (55)
Non-cash charges | 0 | 0
End of period | 88 | 35
Real Estate Related Costs |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 34 | 51
Restructuring charges | 195 | 31
Cash payments | (25) | (26)
Non-cash charges | (148) | (22)
End of period | 56 | 34
Information Technology |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 0 | 2
Restructuring charges | 15 | 23
Cash payments | (6) | (25)
Non-cash charges | (9) | 0
End of period | 0 | 0
Consulting and Other Outside Services |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 0 | 1
Restructuring charges | 106 | 71
Cash payments | (104) | (72)
Non-cash charges | 0 | 0
End of period | $ 2 | $ 0

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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 -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(2) -URI https://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 17 -Subparagraph (f) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3367-108585 + Details
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- Definition Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 45 -Paragraph 3 -URI https://asc.fasb.org/extlink&oid=109237686&loc=d3e17752-110868 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 5.P.3) -URI https://asc.fasb.org/extlink&oid=115931487&loc=d3e140864-122747 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4(b)(1)) -URI https://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747 + Details
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- Definition Carrying amount (including both current and noncurrent portions of the accrual) as of the balance sheet date pertaining to a specified type of cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(2) -URI https://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.P.4(b)(2)) -URI https://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747 + Details
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