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

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Amount of increase (decrease) in the value of a contingent consideration liability, including, but not limited to, differences arising upon settlement.

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Amount of liability recognized arising from contingent consideration in a business combination.

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Amount of assets acquired at the acquisition date.

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Amount of intangible assets, excluding goodwill, acquired at the acquisition date.

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Amount of liabilities assumed at the acquisition date.

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This element represents the aggregate cost of investments accounted for under the equity method of accounting.

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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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Amount of increase in assets, excluding financial assets, lacking physical substance with a definite life, from an acquisition.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Carrying amount of finite-lived intangible assets, indefinite-lived intangible assets and goodwill. Goodwill is an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Intangible assets are assets, not including financial assets, lacking physical substance.

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Amount of cash outflow, not made soon after acquisition date of business combination, to settle contingent consideration liability up to amount recognized at acquisition date, including, but not limited to, measurement period adjustment and less amount paid soon after acquisition date.

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The cash outflow associated with the acquisition of a controlling interest in another entity or an entity that is related to it but not strictly controlled (for example, an unconsolidated subsidiary, affiliate, joint venture or equity method investment).

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The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

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The cash inflow associated with the sale of equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

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Value of stock issued pursuant to acquisitions during the period.

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Significant Transactions - NSM (Details) £ in Millions, $ in Millions									3 Months Ended					9 Months Ended
	Aug. 06, 2021 USD ($)	Apr. 12, 2021 USD ($)	Apr. 12, 2021 GBP (£)	Apr. 07, 2020 USD ($)	Apr. 07, 2020 GBP (£)	Mar. 31, 2019 USD ($)	Dec. 03, 2018 USD ($)	May 18, 2018 USD ($) earnout_period	Sep. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Apr. 07, 2020 GBP (£)
Other Significant Noncash Transactions [Line Items]
Loss on sale										$ 28.7
Goodwill									$ 671.4		$ 525.5			$ 671.4
Change in fair value of contingent consideration earnout liabilities									0.6			$ 0.7		0.8	$ (1.6)
Contingent consideration payments related to acquisitions of subsidiaries														8.8	7.0
Recognized pre-tax expense (revenue)									0.6			$ (0.7)		0.8	$ 1.6
Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Fresh Insurance Services Group Limited
Other Significant Noncash Transactions [Line Items]
Proceeds from sale of business		$ 1.5	£ 1.1
Disposal Group, Held-for-sale, Not Discontinued Operations \| Fresh Insurance Services Group Limited
Other Significant Noncash Transactions [Line Items]
Loss on sale										28.7
Fresh Insurance Services Group Limited
Other Significant Noncash Transactions [Line Items]
Ownership interest (as a percent)								100.00%
Equity method investment, aggregate cost								$ 49.6
Borrowings								$ 51.0
Purchase price adjustment																$ 0.7
Number of earnout periods \| earnout_period								2
KBK Insurance Group, Inc. & KBK Premium Services, Inc.
Other Significant Noncash Transactions [Line Items]
Borrowings							$ 30.1
Cash consideration to acquire businesses and interest in affiliates							60.0
Goodwill						$ 32.6
Intangible assets acquired						32.7
NSM Insurance HoldCo, LLC
Other Significant Noncash Transactions [Line Items]
Cash consideration to acquire businesses and interest in affiliates							$ 29.0
J.C. Taylor Insurance
Other Significant Noncash Transactions [Line Items]
Borrowings	$ 35.0
Cash consideration to acquire businesses and interest in affiliates	49.6
Assets acquired	60.3
Goodwill and other intangible assets	55.7
Liabilities acquired	$ 10.7
Specialty Insurance Distribution (NSM)
Other Significant Noncash Transactions [Line Items]
Contingent consideration									6.7		14.6			6.7
Goodwill and other intangible assets									734.8		736.8			734.8
Specialty Insurance Distribution (NSM) \| Kingsbridge Group Limited
Other Significant Noncash Transactions [Line Items]
Equity method investment, aggregate cost				$ 132.2													£ 107.2
Borrowings				$ 52.4	£ 42.5
Percentage of voting interests acquired				100.00%													100.00%
Stock issued during period, value, acquisitions				$ 80.3
Acquisitions of businesses				111.5
Attribution of acquisition date fair value estimates between goodwill and other intangible assets				20.2
Contingent consideration				$ 4.1					0.1					0.1
Pretax income											4.1
Foreign currency translation gain											$ 0.3
Specialty Insurance Distribution (NSM) \| J.C. Taylor Insurance
Other Significant Noncash Transactions [Line Items]
Percentage of voting interests acquired	100.00%
KBK Insurance Group, Inc. & KBK Premium Services, Inc.
Other Significant Noncash Transactions [Line Items]
Change in fair value of contingent consideration earnout liabilities						$ 5.9
Contingent consideration payments related to acquisitions of subsidiaries										$ 6.7			$ 6.4
KBK Insurance Group, Inc. & KBK Premium Services, Inc. \| Specialty Insurance Distribution (NSM)
Other Significant Noncash Transactions [Line Items]
Contingent consideration									$ 6.6					$ 6.6