Segment Information - Summary of Segment Activity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Segment Reporting Information
Net premiums and contract charges earned	$ 255.9	$ 227.6
Net investment income	97.9	95.5
Net income (loss)	14.5	39.3
Assets	14,427.4		$ 14,383.9
Intersegment eliminations
Segment Reporting Information
Net investment income	(0.6)	(0.6)
Assets	(65.0)		(64.8)
Property & Casualty | Operating segments
Segment Reporting Information
Net premiums and contract charges earned	150.2	155.8
Net investment income	7.2	10.8
Net income (loss)	8.5	27.9
Assets	1,116.3		1,243.4
Life & Retirement
Segment Reporting Information
Assets	11,707.5		12,064.7
Life & Retirement | Operating segments
Segment Reporting Information
Net premiums and contract charges earned	35.8	39.4
Net investment income	84.2	79.9
Net income (loss)	11.8	11.4
Supplemental & Group Benefits | Operating segments
Segment Reporting Information
Net premiums and contract charges earned	69.9	32.4
Net investment income	7.1	5.4
Net income (loss)	11.2	11.3
Assets	1,484.8		858.8
Corporate & Other
Segment Reporting Information
Net investment income	0.0	0.0
Net income (loss)	(17.0)	$ (11.3)
Assets	$ 183.8		$ 281.8