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Business Combination, Contingent and Deferred Consideration

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Business Combination, Fair Value of Previously-held Equity Method Investment

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Cash and Cash Equivalents Held in a Fiduciary Capacity

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Gain on Divestiture of Businesses

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Payments For Previous Acquisition, Deferred and Contingent Consideration

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Percentage of voting equity interests acquired at the acquisition date in the business combination.

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This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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This element represents the amount of earnings or loss of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

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This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

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In a business combination achieved in stages, this element represents the amount of gain recognized by the entity as a result of remeasuring to fair value the equity interest in the acquiree it held before the business combination.

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Amount of gain (loss) from deconsolidation of subsidiary and derecognition of group of assets constituting transfer of business or nonprofit activity, excluding conveyance of oil and gas mineral rights and transfer of good or service in contract with customer.

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Amount before tax of gain (loss) recognized on the sale or disposal of a disposal group. Excludes discontinued operations.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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The number of businesses acquired by the entity during the period.

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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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The cash inflow associated with the amount received from the sale of a portion of the company's business, for example a segment, division, branch or other business, during the period.

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Acquisitions and Dispositions (Narrative) (Details) $ in Millions	1 Months Ended		3 Months Ended	12 Months Ended
	Apr. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2022 USD ($) acquisition	Dec. 31, 2021 USD ($) acquisition	Dec. 31, 2020 USD ($)	Nov. 01, 2022	Oct. 31, 2022	Dec. 01, 2021	Nov. 30, 2021
Business Acquisition [Line Items]
Total purchase consideration				$ 705	$ 1,400
Cash paid				579	888
Estimated contingent consideration				120	153	$ 183
Fair value of previously-held equity method investment				6	390	0
Deferred purchase consideration				158	117	122
Revenue related to acquisitions				58	114	169
Net operating income (loss) related to acquisitions				(5)	3	11
Acquisition-related deposit				24	0	0
Cash and cash equivalents held in a fiduciary capacity				36
Loss on consolidation of entity			$ 39	39	0	$ 0
U.S. Affinity Business
Business Acquisition [Line Items]
Cash proceeds from sale	$ 140
Net gain on disposal	$ 112
Certain Businesses Primarily in the U.S., U.K. and Canada
Business Acquisition [Line Items]
Cash proceeds from sale				15	84
Net gain on disposal					$ 50
Gain on divestiture of businesses				$ 15
Marsh India
Business Acquisition [Line Items]
Percentage of interest acquired		49.00%		92.00%	49.00%				92.00%	49.00%
Step acquisition, remeasurement gain		$ 267
Minimum
Business Acquisition [Line Items]
Revenue target period				2 years	2 years
Minimum \| Marsh India
Business Acquisition [Line Items]
Percentage of interest acquired		49.00%			49.00%
Maximum
Business Acquisition [Line Items]
Revenue target period				4 years	4 years
Maximum \| Marsh India
Business Acquisition [Line Items]
Percentage of interest acquired		92.00%			92.00%
Beassur SARL
Business Acquisition [Line Items]
Percentage of voting interests acquired							70.00%	35.00%
Advance Asset Management
Business Acquisition [Line Items]
Acquisition-related deposit				$ 21
Acquisitions Made In Prior Years
Business Acquisition [Line Items]
Estimated contingent consideration				126	$ 89
Deferred purchase consideration				$ 70	$ 77
Risk and Insurance Services
Business Acquisition [Line Items]
Number of acquisitions made \| acquisition				16	8
Consulting Segment
Business Acquisition [Line Items]
Number of acquisitions made \| acquisition				4	1