Variable Interest Entities (Details) $ in Millions				12 Months Ended
	May 07, 2020 USD ($)	Apr. 04, 2019 USD ($)	Jan. 24, 2018 USD ($)	Dec. 31, 2021 USD ($) director	Dec. 31, 2020 USD ($)	May 06, 2020	May 31, 2019 USD ($)	Apr. 03, 2019	Feb. 05, 2018
Variable Interest Entity [Line Items]
Goodwill				$ 645.5	$ 525.5
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%
First Loss Reinsurance Treaty | BAM
Variable Interest Entity [Line Items]
Percentage of premiums				60.00%
Elementum Holdings, L.P.
Variable Interest Entity [Line Items]
Ownership interest (as a percent)				29.70%	28.90%		30.00%
Other investments				$ 45.0			$ 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%	50.00%
Other investments				$ 129.4
Payments to acquire businesses, gross			$ 41.8
Payments to acquire business			$ 28.3
Additional investment in acquisition	$ 15.0
Kudu
Variable Interest Entity [Line Items]
Ownership interest (as a percent)		99.10%		99.30%	99.30%			49.50%	49.50%
Payments to acquire business		$ 81.4
Assets acquired		155.5
Goodwill		7.6
Intangible assets acquired		2.2
Liabilities acquired		0.8
Noncontrolling interest acquired		$ 1.5
Fully diluted ownership interest (as a percent)		85.40%		84.70%	85.40%			42.70%	42.70%