Segment Information - Additional Significant Financial Information by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
DAC amortization expense	$ 98.7	$ 94.7	$ 99.9
Income tax expense (benefit)	(9.3)	32.1	26.3
Property & Casualty
Segment Reporting Information [Line Items]
DAC amortization expense	64.3	67.7	74.4
Property & Casualty | Operating Segments
Segment Reporting Information [Line Items]
Income tax expense (benefit)	(13.8)	13.2	15.4
Life & Retirement
Segment Reporting Information [Line Items]
DAC amortization expense	32.8	25.5	23.8
Income tax expense (benefit)	6.6	13.6	4.6
Supplemental & Group Benefits
Segment Reporting Information [Line Items]
DAC amortization expense	1.6	1.5	1.7
Supplemental & Group Benefits | Operating Segments
Segment Reporting Information [Line Items]
Income tax expense (benefit)	16.1	12.6	12.0
Corporate & Other | Corporate and Other
Segment Reporting Information [Line Items]
Income tax expense (benefit)	$ (18.2)	$ (7.3)	$ (5.7)