Long-Duration Insurance Contracts - Policyholder Account Balances (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Policyholder Account Balance [Roll Forward]
Beginning balance			$ 5,260.6
Interest credited	$ 50.7	$ 41.4	99.4	$ 81.1
Ending balance	5,206.2		5,206.2		$ 5,260.6
Indexed Universal Life
Policyholder Account Balance [Roll Forward]
Beginning balance	49.9	41.0	47.6	39.1	39.1
Premiums received	3.1	2.5	6.7	4.7
Surrenders and withdrawals	(0.3)	(0.4)	(0.7)	(0.6)
Benefit payments	0.0	0.0	0.0	0.0
Net transfers from (to) separate account	(0.2)	0.0	(0.2)	0.0
Interest credited	0.2	0.3	0.2	0.8
Other	(0.7)	(0.8)	(1.6)	(1.4)
Ending balance	$ 52.0	$ 42.6	$ 52.0	$ 42.6	47.6
Weighted-average crediting rate	(0.10%)	(1.40%)	0.00%	4.10%
Net amount at risk	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Cash surrender value	32.9	1.4	0.0	27.4
Experience Life
Policyholder Account Balance [Roll Forward]
Beginning balance	63.5	65.9	64.3	66.2	66.2
Premiums received	(0.2)	0.0	(0.4)	0.0
Surrenders and withdrawals	(0.6)	(0.8)	(1.5)	(1.5)
Benefit payments	(0.4)	(0.4)	(0.9)	(0.8)
Net transfers from (to) separate account	0.0	0.0	0.0	0.0
Interest credited	0.7	0.7	1.5	1.5
Other	0.0	0.0	0.0	0.0
Ending balance	$ 63.0	$ 65.4	$ 63.0	$ 65.4	64.3
Weighted-average crediting rate	(5.00%)	0.00%	0.00%	5.00%
Net amount at risk	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Cash surrender value	62.8	(0.5)	0.0	64.7
Fixed Account Annuities
Policyholder Account Balance [Roll Forward]
Beginning balance	4,577.4	4,548.2	4,591.1	4,532.7	4,532.7
Premiums received	59.0	47.5	113.9	94.7
Surrenders and withdrawals	(103.9)	(59.5)	(202.0)	(119.8)
Benefit payments	(17.8)	(14.4)	(36.9)	(32.9)
Net transfers from (to) separate account	7.9	15.8	14.5	26.8
Interest credited	39.8	38.3	79.9	77.2
Other	1.1	(2.2)	3.0	(5.0)
Ending balance	$ 4,563.5	$ 4,573.7	$ 4,563.5	$ 4,573.7	4,591.1
Weighted-average crediting rate	0.00%	0.00%	3.60%	3.50%
Net amount at risk	$ (23.3)	$ 12.1	$ 16.2	$ 78.5
Cash surrender value	4,540.9	26.3	109.9	4,515.7
Fixed Indexed Account Annuities
Policyholder Account Balance [Roll Forward]
Beginning balance	498.4	518.2	510.3	522.6	522.6
Premiums received	5.4	8.1	10.5	17.4
Surrenders and withdrawals	(18.6)	(9.4)	(32.5)	(20.3)
Benefit payments	(0.9)	(0.7)	(1.5)	(1.8)
Net transfers from (to) separate account	(2.4)	(0.3)	(3.3)	(0.4)
Interest credited	0.9	1.3	0.9	3.1
Other	(1.6)	1.0	(3.2)	(2.4)
Ending balance	$ 481.2	$ 518.2	$ 481.2	$ 518.2	510.3
Weighted-average crediting rate	0.00%	(0.20%)	0.00%	1.20%
Net amount at risk	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Cash surrender value	486.7	(1.2)	0.0	503.0
SPIA (non-life contingent)
Policyholder Account Balance [Roll Forward]
Beginning balance	33.8	37.0	34.4	37.7	37.7
Premiums received	1.0	0.6	2.1	1.4
Surrenders and withdrawals	(0.1)	(0.1)	(0.2)	(0.4)
Benefit payments	(1.4)	(1.5)	(3.1)	(3.0)
Net transfers from (to) separate account	0.0	0.0	0.0	0.0
Interest credited	0.2	0.3	0.5	0.6
Other	0.0	0.0	(0.2)	0.0
Ending balance	$ 33.5	$ 36.3	$ 33.5	$ 36.3	$ 34.4
Weighted-average crediting rate	(3.00%)	0.00%	0.00%	3.00%
Net amount at risk	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Cash surrender value	$ 33.7	$ (0.7)	$ 0.0	$ 35.9