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Income Taxes (Narrative) (Details) - USD ($) | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 01, 2021 | Nov. 30, 2021
Tax Credit Carryforward [Line Items] |  |  |  |  |
Undistributed earnings of foreign subsidiaries | $ 830,000,000 |  |  |  |
Differences related to non-U.S. operations | 543,000,000 | $ 624,000,000 |  |  |
Net increases in valuation allowances | 1,000,000 | 36,000,000 | $ 72,000,000 |  |
Increase (decrease) in income tax expense due to adjustments to valuation allowance | $ 5,000,000 | 2,000,000 | 14,000,000 |  |
Net operating loss carryforwards (as a percent) | 14.00% |  |  |  |
Unrecognized tax benefits | $ 94,000,000 | 87,000,000 | 90,000,000 |  |
Accrued interest and penalties, before any applicable federal benefit | 48,000,000 | $ 45,000,000 | $ 40,000,000 |  |
Maximum |  |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |  |
Reasonably possible decrease in unrecognized tax benefits | $ 42,000,000 |  |  |  |
Marsh India |  |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |  |
Percentage of interest acquired | 92.00% | 49.00% |  | 92.00% | 49.00%
Marsh India | Minimum |  |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |  |
Percentage of interest acquired |  | 49.00% |  |  |
Marsh India | Maximum |  |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |  |
Percentage of interest acquired |  | 92.00% |  |  |
State and Local |  |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |  |
Differences related to non-U.S. operations | $ 80,000,000 |  |  |  |
Operating loss carryforwards tax benefits | 13,000,000 |  |  |  |
Federal |  |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |  |
Operating loss carryforwards tax benefits | 5,000,000 |  |  |  |
Non-U.S. |  |  |  |  |
Tax Credit Carryforward [Line Items] |  |  |  |  |
Operating loss carryforwards tax benefits | $ 342,000,000 |  |  |  |

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- Definition Amount of decrease reasonably possible in the next twelve months for the unrecognized tax benefit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (d)(3) -URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32718-109319 + Details
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