Business Segments - Segment Operating Profit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021
Segment Reporting Information [Line Items]
Segment Operating Profit (Loss)	$ (68.9)	$ (166.6)		$ (334.0)
Income (Loss) from Change in Fair Value of Equity and Convertible Securities	4.7	(79.9)	[1]	114.6	[1]
Net Realized Investment (Losses) Gains	(18.6)	4.3	[1]	64.8	[1]
Impairment Losses	(1.1)	(25.8)	[1]	(11.0)	[1]
Debt Extinguishment, Pension Settlement, and Other Charges	(70.2)
Loss from Early Extinguishment of Debt	0.0	(3.7)	[2]	0.0	[1]
Goodwill impairment	49.6	0.0	[2]	0.0	[1]
Income (Loss) Attributable to Parent, before Tax	(346.8)	(371.0)		(249.3)
Income (Loss) Attributable to Noncontrolling Interest, before Tax	(0.3)	0.0		0.0
Operating Segments
Segment Reporting Information [Line Items]
Segment Operating Profit (Loss)	(14.0)	(118.9)		(285.6)
Operating Segments | Specialty Property & Casualty Insurance
Segment Reporting Information [Line Items]
Segment Operating Profit (Loss)	(76.3)	(196.9)		(292.1)
Operating Segments | Non-Core Operations
Segment Reporting Information [Line Items]
Segment Operating Profit (Loss)	(22.8)	(36.4)		(39.8)
Operating Segments | Life Insurance
Segment Reporting Information [Line Items]
Segment Operating Profit (Loss)	62.3	78.0		6.5
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Segment Operating Profit (Loss)	(55.2)	(47.7)		(48.4)
Segment Reconciling Items
Segment Reporting Information [Line Items]
Income (Loss) from Change in Fair Value of Equity and Convertible Securities	4.7	(79.9)		114.6
Net Realized Investment (Losses) Gains	(18.6)	4.3		64.8
Impairment Losses	(1.1)	(25.8)		(11.0)
Acquisition and Disposition Related Transaction, Integration, Restructuring and Other Costs	(120.3)	(62.9)		(43.9)
Debt Extinguishment, Pension Settlement, and Other Charges	55.5
Goodwill impairment	$ 45.5	$ 0.0		$ 0.0

[1] As of January 1, 2023, the Company adopted ASU 2018-12 using the modified retrospective method applied as of the transition date of January 1, 2021. Prior period amounts in the financial statements have been recast to reflect application of the new guidance. See Note 2 to the Consolidated Financial Statements for additional information.

[2] As of January 1, 2023, the Company adopted ASU 2018-12 using the modified retrospective method applied as of the transition date of January 1, 2021. Prior period amounts in the financial statements have been recast to reflect application of the new guidance. See Note 2 to the Consolidated Financial Statements for additional information.