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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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Significant Transactions - NSM (Details) £ in Millions, $ in Millions										3 Months Ended	9 Months Ended	12 Months Ended
	Aug. 06, 2021 USD ($)	Apr. 12, 2021 USD ($)	Apr. 12, 2021 GBP (£)	Apr. 07, 2020 USD ($)	Apr. 07, 2020 GBP (£)	Jun. 28, 2019 USD ($)	Apr. 01, 2019 USD ($)	Dec. 03, 2018 USD ($)	May 18, 2018 USD ($) earnout_period	Mar. 31, 2021 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Apr. 07, 2020 GBP (£)
Other Significant Noncash Transactions [Line Items]
Purchases of consolidated subsidiaries, net of cash acquired												$ 39.1	$ 127.3	$ 258.0
Goodwill and intangible assets acquired								$ 59.4
Goodwill												645.5	525.5
Change in fair value of contingent consideration												1.0	(3.3)	2.1
Contingent consideration payments related to acquisitions of subsidiaries												0.0	7.0	7.6
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)		28.7
Fresh Insurance Services Group Limited
Other Significant Noncash Transactions [Line Items]
Ownership interest (as a percent)									100.00%
Proceeds from 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]
Proceeds from borrowings								30.1
Purchases of consolidated subsidiaries, net of cash acquired								60.0
Goodwill														32.6
Intangible assets acquired														32.7
NSM
Other Significant Noncash Transactions [Line Items]
Purchases of consolidated subsidiaries, net of cash acquired								$ 29.0
Embrace Pet Insurance
Other Significant Noncash Transactions [Line Items]
Goodwill							$ 52.2
Intangible assets acquired							15.4
J.C. Taylor Insurance
Other Significant Noncash Transactions [Line Items]
Proceeds from borrowings	$ 35.0
Purchases of consolidated subsidiaries, net of cash acquired	49.6
Goodwill	28.5
Intangible assets acquired	27.2
Assets acquired	60.3
Goodwill and other intangible assets	55.7
Liabilities acquired	$ 10.7
NSM
Other Significant Noncash Transactions [Line Items]
Change in fair value of contingent consideration												1.0	(3.3)
Contingent consideration												6.8	14.6
Goodwill and other intangible assets												725.4	736.8
NSM \| KBK Insurance Group, Inc. & KBK Premium Services, Inc.
Other Significant Noncash Transactions [Line Items]
Contingent consideration payments related to acquisitions of subsidiaries												8.8	7.0
NSM \| Fresh Insurance Services Group Limited
Other Significant Noncash Transactions [Line Items]
Equity method investment, aggregate cost									$ 49.6
NSM \| Embrace Pet Insurance
Other Significant Noncash Transactions [Line Items]
Proceeds from borrowings							$ 20.4
Percentage of voting interests acquired							100.00%
Payments to acquire businesses, gross							$ 71.5
Additional investment in acquisition							$ 58.2
NSM \| Kingsbridge Group Limited
Other Significant Noncash Transactions [Line Items]
Equity method investment, aggregate cost				$ 132.2											£ 107.2
Proceeds from borrowings				$ 52.4	£ 42.5
Percentage of voting interests acquired				100.00%											100.00%
Additional investment in acquisition				$ 80.3
Acquisitions of businesses													111.5
Finite-lived Intangible Assets Acquired													20.2
Pretax income												(0.3)	4.1
Contingent consideration				$ 4.1									0.3
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														$ 5.9
Contingent consideration payments related to acquisitions of subsidiaries												$ 6.7	$ 6.4
AIG Collector Car Business
Other Significant Noncash Transactions [Line Items]
Purchases of consolidated subsidiaries, net of cash acquired						$ 82.5
Intangible assets acquired						82.5
Additional investment in acquisition						59.1
AIG Collector Car Business \| NSM
Other Significant Noncash Transactions [Line Items]
Proceeds from borrowings						$ 22.5