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Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenue | $ 2,385 | $ 2,379 | $ 8,101 | $ 8,128
United States |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenue | 1,169 | 1,209 | 3,503 | 3,516
Americas other than United States |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenue | 200 | 256 | 647 | 723
United Kingdom |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenue | 332 | 358 | 1,276 | 1,210
Ireland |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenue | 19 | 17 | 63 | 59
Europe, Middle East, & Africa other than United Kingdom and Ireland |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenue | 372 | 266 | 1,731 | 1,734
Asia Pacific |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenue | 293 | 273 | 881 | 886
Elimination |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenue | (6) | (3) | (13) | (11)
Commercial Risk Solutions | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenue | 1,042 | 1,057 | 3,314 | 3,342
Reinsurance Solutions | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenue | 321 | 291 | 1,617 | 1,499
Retirement Solutions | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenue | 468 | 484 | 1,258 | 1,323
Health Solutions | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenue | 282 | 279 | 1,042 | 1,082
Data & Analytic Services | Operating Segments |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenue | $ 278 | $ 271 | $ 883 | $ 893

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- Definition Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 30 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 40 -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9031-108599 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 41 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9038-108599 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 32 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 32 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130543-203045 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 22 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 22 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 42 -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599 Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130545-203045 Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 924 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 11.L) -URI http://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856 + Details
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