Long-Duration Insurance Contracts - Policyholder Account Balances (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Policyholder Account Balance [Roll Forward]
Beginning balance	$ 5,064.1
Interest credited	53.8	$ 52.8
Ending balance	5,056.1
Indexed Universal Life
Policyholder Account Balance [Roll Forward]
Beginning balance	95.5	72.9
Premiums received	6.7	6.0
Surrenders and withdrawals	(0.9)	(0.4)
Benefit payments	0.0	0.0
Net transfers from (to) separate account	(0.3)	(0.1)
Interest credited	0.8	1.0
Other	(1.2)	(1.2)
Ending balance	$ 100.6	$ 78.2
Weighted-average crediting rate	3.50%	5.30%
Net amount at risk	$ 0.0	$ 0.0
Cash surrender value	77.9	59.3
Experience life
Policyholder Account Balance [Roll Forward]
Beginning balance	54.8	58.0
Premiums received	(0.2)	(0.2)
Surrenders and withdrawals	(0.9)	(0.8)
Benefit payments	(0.5)	(0.3)
Net transfers from (to) separate account	0.0	0.0
Interest credited	0.6	0.7
Other	(0.1)	0.0
Ending balance	$ 53.7	$ 57.4
Weighted-average crediting rate	4.90%	4.90%
Net amount at risk	$ 0.0	$ 0.0
Cash surrender value	53.1	56.8
Fixed Account Annuities
Policyholder Account Balance [Roll Forward]
Beginning balance	4,486.8	4,508.4
Premiums received	36.3	43.4
Surrenders and withdrawals	(74.0)	(89.2)
Benefit payments	(15.0)	(21.8)
Net transfers from (to) separate account	8.9	12.0
Interest credited	41.4	42.7
Other	(1.8)	0.4
Ending balance	$ 4,482.6	$ 4,495.9
Weighted-average crediting rate	3.80%	3.90%
Net amount at risk	$ 28.3	$ 31.8
Cash surrender value	4,433.8	4,447.4
Fixed Indexed Account Annuities
Policyholder Account Balance [Roll Forward]
Beginning balance	373.3	409.5
Premiums received	2.9	4.2
Surrenders and withdrawals	(9.9)	(13.2)
Benefit payments	(1.0)	(1.7)
Net transfers from (to) separate account	(0.1)	(0.2)
Interest credited	1.4	3.4
Other	(1.5)	(2.3)
Ending balance	$ 365.1	$ 399.7
Weighted-average crediting rate	1.60%	3.50%
Net amount at risk	$ 0.0	$ 0.0
Cash surrender value	360.7	393.1
SPIA (non-life contingent)
Policyholder Account Balance [Roll Forward]
Beginning balance	26.1	28.6
Premiums received	1.1	0.6
Surrenders and withdrawals	(0.1)	(0.2)
Benefit payments	(1.1)	(1.2)
Net transfers from (to) separate account	0.0	0.0
Interest credited	0.2	0.3
Other	0.0	0.2
Ending balance	$ 26.2	$ 28.3
Weighted-average crediting rate	3.30%	4.20%
Net amount at risk	$ 0.0	$ 0.0
Cash surrender value	$ 25.8	$ 28.0