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Variable Interest Entities (Details) $ in Millions			3 Months Ended	12 Months Ended
	May 07, 2020 USD ($)	Jan. 24, 2018 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2022 USD ($) director	Dec. 31, 2021 USD ($)	May 06, 2020	May 31, 2019 USD ($)
Private equity funds
Variable Interest Entity [Line Items]
Trading security, fair value			$ 140.6	$ 140.6	$ 141.8
Outrigger Re
Variable Interest Entity [Line Items]
Purchase price			$ 205.0
Ownership interest after all transactions (as a percent)			100.00%
BAM
Variable Interest Entity [Line Items]
Number directors to designate for election | director				2
First Loss Reinsurance Treaty | HG Global
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured			15.00%	15.00%
First Loss Reinsurance Treaty | BAM
Variable Interest Entity [Line Items]
Percentage of premiums			60.00%	60.00%
Elementum Holdings, L.P.
Variable Interest Entity [Line Items]
Ownership interest (as a percent)			29.70%	29.70%	29.70%		30.00%
Other investments			$ 30.0	$ 30.0			$ 55.1
DavidShield
Variable Interest Entity [Line Items]
Ownership interest (as a percent)		50.00%
PassportCard
Variable Interest Entity [Line Items]
Ownership interest (as a percent)		50.00%
PassportCard/DavidShield
Variable Interest Entity [Line Items]
Ownership interest (as a percent)	53.80%		53.80%	53.80%	53.80%	50.00%
Other investments			$ 144.6	$ 144.6
Payments to acquire businesses, gross		$ 41.8
Payments to acquire business		$ 28.3
Additional investment in acquisition	$ 15.0

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