Information About Segments of Business Textuals (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information
Number of major segments | segment	3
Net premiums earned	$ 6,445.9	$ 7,342.1	$ 7,559.8
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal	$ 45.6
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal, Statement of Income or Comprehensive Income [Extensible Enumeration]	Consolidated revenues
General Insurance Group [Member]
Segment Reporting Information
Interest - other	$ 76.5	68.9	63.5
Title Insurance Group [Member]
Segment Reporting Information
Interest - other	$ 0.0	$ 0.8	$ 1.9
Commercial Automobile [Member]
Segment Reporting Information
Commercial auto net premiums earned	41.00%