Segment Information - Summary of Segment Activity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Segment Reporting Information
Net premiums and contract charges earned	$ 255.9	$ 255.8
Net investment income	100.4	97.9
Net income (loss)	6.6	20.3
Assets	13,653.9		$ 13,306.1
Intersegment eliminations
Segment Reporting Information
Net investment income	(0.6)	(0.6)
Assets	(54.3)		(64.9)
Property & Casualty | Operating segments
Segment Reporting Information
Net premiums and contract charges earned	152.4	150.2
Net investment income	4.0	7.2
Net income (loss)	(11.6)	8.5
Assets	1,077.0		1,083.8
Life & Retirement | Operating segments
Segment Reporting Information
Net premiums and contract charges earned	37.7	35.8
Net investment income	87.9	84.2
Net income (loss)	14.0	15.6
Assets	11,085.1		10,754.5
Supplemental & Group Benefits | Operating segments
Segment Reporting Information
Net premiums and contract charges earned	65.8	69.8
Net investment income	9.1	7.1
Net income (loss)	14.0	13.2
Assets	1,377.1		1,359.3
Corporate & Other
Segment Reporting Information
Net investment income	0.0	0.0
Net income (loss)	(9.8)	$ (17.0)
Assets	$ 169.0		$ 173.4