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Commitments and Contingencies (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Loss Contingencies [Line Items]
Net gain from sale of discontinued operations, net of tax	$ (0.7)	$ 0.9	$ (0.8)	$ 1.6
Sirius Group \| Swedish Tax Authority
Loss Contingencies [Line Items]
Contingent liability	17.2		17.2		$ 16.5
Sirius Group \| Swedish Tax Authority \| Sirius Group
Loss Contingencies [Line Items]
Change in contingent liability	$ (0.7)		$ (0.7)