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Variable Interest Entities (Details) $ in Millions		12 Months Ended
	Apr. 04, 2019 USD ($)	Dec. 31, 2019 USD ($) director	May 31, 2019 USD ($)	Apr. 03, 2019	Dec. 31, 2018 USD ($)	Feb. 05, 2018 USD ($)
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured		15.00%
Other Investments		$ 622.8			$ 165.7
Payments to acquire business, net	$ 81.4
Goodwill		$ 394.7			379.9
BAM
Variable Interest Entity [Line Items]
Right to elect directors on board number | 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)		30.00%	30.00%
Other Investments			$ 55.1
Kudu
Variable Interest Entity [Line Items]
Ownership interest (as a percent)	99.10%			49.50%		49.50%
Assets acquired	$ 155.5					$ 155.5
Fully diluted ownership interest (as a percent)	85.40%			42.70%		42.70%
Goodwill	$ 7.6					$ 7.6
Intangible assets acquired	2.2					2.2
Liabilities acquired	0.8					0.8
Noncontrolling interest acquired	$ 1.5					$ 1.5
Elementum Holdings, L.P.
Variable Interest Entity [Line Items]
Other Investments		$ 55.1			$ 0.0

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This element represents the fair value of the noncontrolling interest in the acquiree at the acquisition date.

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