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 ($)	Apr. 07, 2020 GBP (£)	Jun. 28, 2019 USD ($)	Apr. 01, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 03, 2018 USD ($)	May 18, 2018 USD ($) earnout_period	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2021 USD ($)
Other Significant Noncash Transactions [Line Items]
Loss on sale												$ 28.7
Goodwill											$ 641.4				$ 645.5
Change in fair value of contingent consideration earnout liabilities											0.1
Contingent consideration payments related to acquisitions of subsidiaries											0.0	6.7
Recognized pre-tax expense (revenue)											0.1
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%
Borrowings										$ 51.0
Purchase price adjustment														$ 0.7
Number of earnout periods | earnout_period										2
Cash consideration to acquire businesses and interest in affiliates										$ 49.6
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
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]
Borrowings	$ 35.0
Cash consideration to acquire businesses and interest in affiliates	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
Specialty Insurance Distribution (NSM)
Other Significant Noncash Transactions [Line Items]
Goodwill and other intangible assets											712.0				725.4
Contingent consideration											$ 0.0				$ 6.8
Specialty Insurance Distribution (NSM) | Embrace Pet Insurance
Other Significant Noncash Transactions [Line Items]
Ownership interest (as a percent)							100.00%
Borrowings							$ 20.4
Cash consideration to acquire businesses and interest in affiliates							71.5
Stock issued during period, value, acquisitions							$ 58.2
Specialty Insurance Distribution (NSM) | Kingsbridge Group Limited
Other Significant Noncash Transactions [Line Items]
Borrowings				$ 52.4	£ 42.5
Stock issued during period, value, acquisitions				$ 80.3
Percentage of voting interests acquired				100.00%	100.00%
Goodwill acquired				$ 111.5
Finite-lived Intangible Assets Acquired				20.2
Specialty Insurance Distribution (NSM) | Kingsbridge Group Limited | United Kingdom, Pounds
Other Significant Noncash Transactions [Line Items]
Cash consideration to acquire businesses and interest in affiliates | £					£ 107.2
Specialty Insurance Distribution (NSM) | Kingsbridge Group Limited | United States of America, Dollars
Other Significant Noncash Transactions [Line Items]
Cash consideration to acquire businesses and interest in affiliates				$ 132.2
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												$ 6.8	$ 6.7
AIG Collector Car Business
Other Significant Noncash Transactions [Line Items]
Cash consideration to acquire businesses and interest in affiliates						$ 82.5
Intangible assets acquired						82.5
Stock issued during period, value, acquisitions						59.1
AIG Collector Car Business | Specialty Insurance Distribution (NSM)
Other Significant Noncash Transactions [Line Items]
Borrowings						$ 22.5