Long-Duration Insurance Contracts - Policyholder Account Balances (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Policyholder Account Balance [Roll Forward]
Beginning balance	$ 5,260.6
Interest credited	48.7	$ 39.7
Ending balance	5,234.6		$ 5,260.6
Indexed Universal Life
Policyholder Account Balance [Roll Forward]
Beginning balance	47.6	39.1	39.1
Premiums received	3.6	2.2
Surrenders and withdrawals	(0.4)	(0.2)
Benefit payments	0.0	0.0
Net transfers from (to) separate account	0.0	0.0
Interest credited	0.0	0.5
Other	(0.9)	(0.6)
Ending balance	$ 49.9	$ 41.0	47.6
Weighted-average crediting rate	0.10%	5.40%
Net amount at risk	$ 0.0	$ 0.0
Cash surrender value	32.9	26.0
Experience Life
Policyholder Account Balance [Roll Forward]
Beginning balance	64.3	66.2	66.2
Premiums received	(0.2)	0.0
Surrenders and withdrawals	(0.9)	(0.7)
Benefit payments	(0.5)	(0.4)
Net transfers from (to) separate account	0.0	0.0
Interest credited	0.8	0.8
Other	0.0	0.0
Ending balance	$ 63.5	$ 65.9	64.3
Weighted-average crediting rate	5.00%	5.00%
Net amount at risk	$ 0.0	$ 0.0
Cash surrender value	62.8	65.2
Fixed Account Annuities
Policyholder Account Balance [Roll Forward]
Beginning balance	4,591.1	4,532.7	4,532.7
Premiums received	54.9	47.2
Surrenders and withdrawals	(98.1)	(60.3)
Benefit payments	(19.1)	(18.5)
Net transfers from (to) separate account	6.6	11.0
Interest credited	40.1	38.9
Other	1.9	(2.8)
Ending balance	$ 4,577.4	$ 4,548.2	4,591.1
Weighted-average crediting rate	3.60%	3.50%
Net amount at risk	$ 39.5	$ 66.4
Cash surrender value	4,540.9	4,489.4
Fixed Indexed Account Annuities
Policyholder Account Balance [Roll Forward]
Beginning balance	510.3	522.6	522.6
Premiums received	5.1	9.3
Surrenders and withdrawals	(13.9)	(10.9)
Benefit payments	(0.6)	(1.1)
Net transfers from (to) separate account	(0.9)	(0.1)
Interest credited	0.0	1.8
Other	(1.6)	(3.4)
Ending balance	$ 498.4	$ 518.2	510.3
Weighted-average crediting rate	0.00%	1.40%
Net amount at risk	$ 0.0	$ 0.0
Cash surrender value	486.7	504.2
SPIA (non-life contingent)
Policyholder Account Balance [Roll Forward]
Beginning balance	34.4	37.7	37.7
Premiums received	1.1	0.8
Surrenders and withdrawals	(0.1)	(0.3)
Benefit payments	(1.7)	(1.5)
Net transfers from (to) separate account	0.0	0.0
Interest credited	0.3	0.3
Other	(0.2)	0.0
Ending balance	$ 33.8	$ 37.0	$ 34.4
Weighted-average crediting rate	3.00%	3.00%
Net amount at risk	$ 0.0	$ 0.0
Cash surrender value	$ 33.7	$ 36.6