Schedule VI - Supplementary Information for Property-Casualty Insurance Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Abstract]
Deferred acquisition costs and value of business acquired, net	$ 218.8	$ 68.6	$ 92.2
Loss and loss adjustment expense reserves	4,841.4	1,310.1	1,111.7
Unearned premium reserves	1,198.4	284.8	336.2
Net premiums earned	1,717.0	610.8	700.1
Total realized and unrealized investment gains and net investment income	312.5	278.9	282.5
Loss and loss expenses incurred related to current year	1,369.1	431.5	490.0
Loss and loss expenses incurred related to prior year	(42.6)	33.8	(86.5)
Acquisition costs, net	387.8	187.1	295.6
Net paid losses and loss expenses	1,450.1	283.1	252.0
Net premiums written	$ 1,734.2	$ 542.2	$ 657.0