Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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Acquisitions and Dispositions of Businesses - Completed Acquisitions Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) numberOfAcquisition	Dec. 31, 2019 numberOfAcquisition	Apr. 06, 2020	Jan. 31, 2020	Jan. 03, 2020	Jan. 01, 2020
Business Acquisition [Line Items]
Number of business acquired under business combination \| numberOfAcquisition	6	3
Weighted average useful life	6 years
Revenues from acquisitions included in the Company's Consolidated Statement of Income	$ 44
Farmington Administrative Services LLC
Business Acquisition [Line Items]
Percentage of capital acquired			100.00%
Cytelligence Inc.
Business Acquisition [Line Items]
Percentage of capital acquired				100.00%
Cover Wallet Inc.
Business Acquisition [Line Items]
Percentage of capital acquired					100.00%
TRIUM GmbH Insurance Broker
Business Acquisition [Line Items]
Percentage of capital acquired						100.00%
Assimedia SA
Business Acquisition [Line Items]
Percentage of capital acquired						100.00%
Apollo Conseilet Courtage
Business Acquisition [Line Items]
Percentage of capital acquired						100.00%
Other general expense
Business Acquisition [Line Items]
Acquisition related costs	$ 7