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Fiduciary Assets and Liabilities (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Dec. 31, 2020
Fiduciary Assets and Liabilities [Line Items] |  |  |  |  |
Net uncollected premiums and claims receivable and payable | $ 14,200 |  | $ 14,200 |  | $ 11,200
Risk and Insurance Services Segment |  |  |  |  |
Fiduciary Assets and Liabilities [Line Items] |  |  |  |  |
Interest on fiduciary funds | 3 | $ 9 | 8 | $ 32 |
Operating Segments | Risk and Insurance Services Segment |  |  |  |  |
Fiduciary Assets and Liabilities [Line Items] |  |  |  |  |
Interest on fiduciary funds | $ 3 | $ 9 | $ 8 | $ 32 |

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- Definition Fiduciary Assets and Liabilities [Line Items] + References No definition available. + Details
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- Definition Interest income earned on both U.S. and foreign fiduciary funds held in trust. + References No definition available. + Details
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- Definition Net uncollected premiums and claims and the related payables are not assets and liabilities of MMC and are not included in the accompanying consolidated balance sheets. + References No definition available. + Details
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- Details
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Namespace Prefix: |
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Period Type: |

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- Details
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Period Type: |