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Restructuring Costs (Restructuring Activity) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020
Restructuring Reserve [Roll Forward] |  |
Beginning of period | $ 81 | $ 102
Amounts Accrued | 70 | 89
Cash payments | (98) | (100)
Non-Cash/Other | (5) | (10)
End of period | 48 | 81
Severance |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 36 | 51
Amounts Accrued | 24 | 39
Cash payments | (42) | (54)
Non-Cash/Other |  | 0
End of period | 18 | 36
Future rent under non-cancelable leases and other costs |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 45 | 51
Amounts Accrued | 46 | 50
Cash payments | (56) | (46)
Non-Cash/Other | (5) | (10)
End of period | 30 | 45
JLT Transaction |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 25 | 47
Amounts Accrued | 93 | 251
Cash payments | (80) | (226)
Non-cash charges | (17) | (47)
End of period | 21 | 25
JLT Transaction | Severance |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 16 | 42
Amounts Accrued | 14 | 43
Cash payments | (13) | (69)
Non-cash charges | 0 | 0
End of period | 17 | 16
JLT Transaction | Real Estate Related Costs |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 7 | 5
Amounts Accrued | 26 | 69
Cash payments | (12) | (25)
Non-cash charges | (17) | (42)
End of period | 4 | 7
JLT Transaction | Information Technology |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 2 | 0
Amounts Accrued | 23 | 62
Cash payments | (25) | (55)
Non-cash charges | 0 | (5)
End of period | 0 | 2
JLT Transaction | Consulting and Other Outside Services |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 0 | 0
Amounts Accrued | 30 | 77
Cash payments | (30) | (77)
Non-cash charges | 0 | 0
End of period | $ 0 | $ 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 http://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 http://asc.fasb.org/extlink&oid=123570139&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 http://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 http://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 http://asc.fasb.org/extlink&oid=123570139&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 http://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 http://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 http://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747 + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition Amount of decrease in the reserve for full or partial settlement through consideration other than cash. + 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 http://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 http://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747 + Details
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- Definition Amount of foreign currency translation gain (loss) which decreases (increases) the restructuring reserve. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(2) -URI http://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 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4(b)(2)) -URI http://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747 + Details
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