Goodwill and Intangible Assets - Schedule of Goodwill by Segment (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Goodwill [Roll Forward]
Goodwill	$ 1,250.7	$ 1,300.3	[1]
Specialty Property & Casualty Insurance
Goodwill [Roll Forward]
Goodwill	1,043.0	1,043.0
Non-Core Operations
Goodwill [Roll Forward]
Goodwill	0.0	49.6
Life Insurance
Goodwill [Roll Forward]
Goodwill	$ 207.7	$ 207.7

[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.