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Debt - Schedule of the Change in Debt under the NSM Bank Facility (Details) £ in Millions, $ in Millions			3 Months Ended		9 Months Ended
	Apr. 07, 2020 USD ($)	Apr. 07, 2020 GBP (£)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)
Debt Instrument
Beginning balance					$ 376.4
Repayments					(105.9)	$ (2.7)
Ending balance			$ 710.4		710.4
Term Loan | NSM Bank Facility
Debt Instrument
Beginning balance					271.3
Ending balance			293.7		293.7
Specialty Insurance Distribution (NSM)
Debt Instrument
Beginning balance					272.6
Ending balance			295.0		295.0
Specialty Insurance Distribution (NSM) | NSM Bank Facility
Debt Instrument
Beginning balance			276.6	$ 273.4	277.4	221.3
Ending balance			300.4	275.0	300.4	275.0
Specialty Insurance Distribution (NSM) | Term Loan | NSM Bank Facility
Debt Instrument
Borrowings	$ 52.4	£ 42.5	0.0	0.0	0.0	52.4
Repayments			(0.7)	(0.7)	(2.1)	(1.3)
Foreign currency translation			(1.5)	2.3	(0.9)	2.6
Specialty Insurance Distribution (NSM) | Revolving credit loan | NSM Bank Facility
Debt Instrument
Borrowings			35.0	0.0	35.0	0.0
Repayments			$ (9.0)	$ 0.0	$ (9.0)	$ 0.0

X

- Definition

Amount of increase (decrease) in debt instruments, classified as other.

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+ References

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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- Definition

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

+ References

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-Publisher FASB
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The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

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