Business Segments - Segment Net Operating Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information [Line Items]
Segment Net Operating Income (Loss)	$ (27.9)	$ (27.0)	$ (97.8)	$ (92.9)
Loss from Early Extinguishment of Debt	0.0	0.0	0.0	(3.7)
Goodwill, pre tax impairment charge	0.0	0.0	(49.6)	0.0
Net Loss	(146.3)	(74.8)	(323.5)	(233.3)
Net Loss	(146.4)	(74.8)	(323.6)	(233.3)
Less: Net Loss attributable to Noncontrolling Interest	(0.1)	0.0	(0.1)	0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	(70.2)	0.0	(70.2)	(3.7)
Operating Segments
Segment Reporting Information [Line Items]
Segment Net Operating Income (Loss)	(18.5)	(14.7)	(65.6)	(66.5)
Operating Segments | Specialty Property & Casualty Insurance
Segment Reporting Information [Line Items]
Segment Net Operating Income (Loss)	(33.2)	(28.7)	(102.4)	(112.3)
Operating Segments | Preferred Property & Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Segment Net Operating Income (Loss)	(7.3)	(2.1)	(19.5)	(25.0)
Operating Segments | Life Insurance
Segment Reporting Information [Line Items]
Segment Net Operating Income (Loss)	14.7	14.0	36.8	45.8
Corporate and Other
Segment Reporting Information [Line Items]
Segment Net Operating Income (Loss)	(9.4)	(12.3)	(32.2)	(26.4)
Other	(9.4)	(12.3)	(32.2)	(26.4)
Segment Reconciling Items
Segment Reporting Information [Line Items]
Change in Fair Value of Equity and Convertible Securities	2.3	(8.8)	5.5	(63.1)
Net Realized Investment (Losses) Gains	(22.9)	(9.6)	(30.3)	0.3
Impairment Gains (Losses)	(0.8)	(6.6)	0.1	(17.5)
Acquisition and Disposition Related Transaction, Integration, Restructuring and Other Costs	(34.2)	(20.7)	(80.5)	(32.2)
Goodwill, pre tax impairment charge	0.0	0.0	(45.5)	0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	$ (55.5)	$ 0.0	$ (55.5)	$ (2.9)