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Business Combination, Contingent and Deferred Consideration

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Payments For Previous Acquisition, Deferred Consideration

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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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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			9 Months Ended		12 Months Ended
	Apr. 30, 2022 USD ($)	Sep. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) acquisition	Sep. 30, 2021 USD ($)	Dec. 31, 2021 acquisition	Nov. 30, 2021
Business Acquisition [Line Items]
Total consideration					$ 227	$ 546
Cash paid					210	405
Estimated fair value of deferred/contingent consideration					17	141
Deferred purchase consideration from prior years' acquisitions					116	84
Contingent consideration from prior year's acquisitions					28	26
Deconsolidation of Russian businesses			$ (39)		(39)	0
U.S. Affinity Business
Business Acquisition [Line Items]
Disposal group, consideration	$ 140
Gain on disposal	$ 112
Certain Businesses Primarily in the U.S. and U.K.
Business Acquisition [Line Items]
Disposal group, consideration						84
Gain on disposal						50
Certain Businesses Primarily in Brazil
Business Acquisition [Line Items]
Disposal group, consideration					7
Marsh India Insurance Brokers Limited
Business Acquisition [Line Items]
Percentage of ownership in equity investment							92.00%	49.00%
Prior Fiscal Periods Acquisitions
Business Acquisition [Line Items]
Deferred purchase consideration from prior years' acquisitions						84
Contingent consideration from prior year's acquisitions					66	72
Pro forma revenue				$ 38		73
Operating income (loss) related to acquisitions				$ 3		$ 4
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Total consideration					227
Cash paid					210
Estimated fair value of deferred/contingent consideration					17
Pro forma revenue		$ 16			22
Operating income (loss) related to acquisitions		$ (1)			$ (1)
Risk and Insurance Services
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions) \| acquisition					8		8
Consulting
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions) \| acquisition					3		1
Minimum
Business Acquisition [Line Items]
Revenue target period (in years)					2 years	2 years
Maximum
Business Acquisition [Line Items]
Revenue target period (in years)					4 years	4 years