Goodwill and Intangible Assets - Goodwill Rollforward (Details) - USD ($) $ in Millions		12 Months Ended
	Oct. 01, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Goodwill [Roll Forward]
Goodwill at the beginning of the period		$ 77.1	$ 77.1	$ 77.1
Accumulated impairment losses at the beginning of the period		(33.6)	(33.6)	(28.0)
Goodwill, net at the beginning of the period		43.5	43.5	49.1
Acquisitions		12.8	0.0	0.0
Impairments	$ (2.0)	(2.0)	0.0	(5.6)
Goodwill at the end of the period		89.9	77.1	77.1
Accumulated impairment losses at the end of the period		(35.6)	(33.6)	(33.6)
Goodwill, net at the end of the period		54.3	43.5	43.5
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		(33.6)	(33.6)	(28.0)
Goodwill, net at the beginning of the period		14.4	14.4	20.0
Acquisitions		0.0	0.0	0.0
Impairments		(2.0)	0.0	(5.6)
Goodwill at the end of the period		48.0	48.0	48.0
Accumulated impairment losses at the end of the period		(35.6)	(33.6)	(33.6)
Goodwill, net at the end of the period		12.4	14.4	14.4
Supplemental & Group Benefits
Goodwill [Roll Forward]
Goodwill at the beginning of the period		19.6	19.6	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		19.6	19.6	19.6
Acquisitions		12.8	0.0	0.0
Impairments		0.0	0.0	0.0
Goodwill at the end of the period		32.4	19.6	19.6
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	$ 19.6	$ 19.6