Business Segments - Segment Operating Profit (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]
Operating Income (Loss)	$ (39.0)	$ (40.2)	$ (132.0)	$ (131.1)
Loss before Income Taxes	(190.8)	(87.8)	(410.6)	(298.1)
Corporate and Other Adjusted Operating Loss From:
Income (Loss) from Change in Fair Value of Equity and Convertible Securities	2.8	(11.2)	6.9	(79.9)
Debt and Equity Securities, Realized Gain (Loss)			(38.3)	0.4
Impairment Gains (Losses)	(1.1)	(8.3)	0.1	(22.1)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	(70.2)	0.0	(70.2)	(3.7)
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
Loss before Income Taxes	(190.7)	(87.8)	(410.5)	(298.1)
Less: Net Loss attributable to Noncontrolling Interest	(0.1)	0.0	(0.1)	0.0
Operating Segments
Segment Reporting Information [Line Items]
Operating Income (Loss)	(25.7)	(23.6)	(90.5)	(98.9)
Operating Segments | Specialty Property & Casualty Insurance
Segment Reporting Information [Line Items]
Operating Income (Loss)	(43.2)	(39.2)	(132.9)	(150.4)
Operating Segments | Preferred Property & Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	(9.6)	(3.3)	(25.5)	(34.4)
Operating Segments | Life Insurance
Segment Reporting Information [Line Items]
Operating Income (Loss)	17.5	15.6	42.4	51.5
Corporate and Other
Segment Reporting Information [Line Items]
Operating Income (Loss)	(13.3)	(16.6)	(41.5)	(32.2)
Corporate and Other Adjusted Operating Loss From:
Other	(13.3)	(16.6)	(41.5)	(32.2)
Segment Reconciling Items
Corporate and Other Adjusted Operating Loss From:
Income (Loss) from Change in Fair Value of Equity and Convertible Securities	2.8	(11.2)	6.9	(79.9)
Debt and Equity Securities, Realized Gain (Loss)	(30.3)	(12.1)	(38.3)	0.4
Impairment Gains (Losses)			0.1	(22.1)
Acquisition and Disposition Related Transaction, Integration, Restructuring and Other Costs	(43.3)	(12.7)	(101.9)	(27.3)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	(55.5)	0.0	(55.5)	(2.9)
Goodwill, pre tax impairment charge	$ 0.0	$ 0.0	$ (45.5)	$ 0.0