Goodwill and Intangible Assets - Goodwill Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Goodwill [Roll Forward]
Goodwill at the beginning of the period	$ 89.9	$ 89.9	$ 77.1
Accumulated impairment losses at the beginning of the period	(35.6)	(35.6)	(33.6)
Goodwill, net at the beginning of the period	54.3	54.3	43.5
Acquisitions	0.0	0.0	12.8
Impairments	0.0	0.0	(2.0)
Goodwill at the end of the period	89.9	89.9	89.9
Accumulated impairment losses at the end of the period	(35.6)	(35.6)	(35.6)
Goodwill, net at the end of the period	54.3	54.3	54.3
Property & Casualty
Goodwill [Roll Forward]
Goodwill at the beginning of the period	9.5	9.5	9.5
Accumulated impairment losses at the beginning of the period	0.0	0.0	0.0
Goodwill, net at the beginning of the period	9.5	9.5	9.5
Acquisitions	0.0	0.0	0.0
Impairments	0.0	0.0	0.0
Goodwill at the end of the period	9.5	9.5	9.5
Accumulated impairment losses at the end of the period	0.0	0.0	0.0
Goodwill, net at the end of the period	9.5	9.5	9.5
Life & Retirement
Goodwill [Roll Forward]
Goodwill at the beginning of the period	48.0	48.0	48.0
Accumulated impairment losses at the beginning of the period	(35.6)	(35.6)	(33.6)
Goodwill, net at the beginning of the period	12.4	12.4	14.4
Acquisitions	0.0	0.0	0.0
Impairments	0.0	0.0	(2.0)
Goodwill at the end of the period	48.0	48.0	48.0
Accumulated impairment losses at the end of the period	(35.6)	(35.6)	(35.6)
Goodwill, net at the end of the period	12.4	12.4	12.4
Supplemental & Group Benefits
Goodwill [Roll Forward]
Goodwill at the beginning of the period	32.4	32.4	19.6
Accumulated impairment losses at the beginning of the period	0.0	0.0	0.0
Goodwill, net at the beginning of the period	32.4	32.4	19.6
Acquisitions	0.0	0.0	12.8
Impairments	0.0	0.0	0.0
Goodwill at the end of the period	32.4	32.4	32.4
Accumulated impairment losses at the end of the period	0.0	0.0	0.0
Goodwill, net at the end of the period	$ 32.4	$ 32.4	$ 32.4