Schedule II Condensed Financial Information of Registrant - Condensed Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021
Revenues
Net investment income									$ 444.8	$ 400.9	[1]	$ 422.5	[1]
Net investment losses									(24.0)	(56.5)	[1]	(11.0)	[1]
Total revenues	$ 346.4	$ 342.6	$ 345.9	$ 346.7	$ 331.2	$ 329.4	$ 346.9	$ 321.7	1,491.9	1,381.6	[1]	1,329.3	[1]
Expenses
Interest expense									29.7	19.4	[1]	13.9	[1]
Total benefits, losses and expenses									1,438.6	1,365.1	[1]	1,119.2	[1]
Income tax expense (benefit)									8.3	(3.3)	[1]	39.7	[1]
Net income	$ (16.7)	$ 20.4	$ (4.2)	$ 20.3	$ 46.9	$ 20.2	$ 54.2	$ 49.1	45.0	19.8	[1],[2]	170.4	[1],[2]
Parent company
Revenues
Net investment income									0.2	0.0		(0.1)
Total revenues									0.2	0.0		(0.1)
Expenses
Interest expense									29.7	19.4		13.8
Other									5.1	8.4		11.2
Total benefits, losses and expenses									34.8	27.8		25.0
Loss before income tax benefit and equity in net earnings of subsidiaries									(34.6)	(27.8)		(25.1)
Income tax expense (benefit)									(6.9)	(6.3)		(5.4)
Loss before equity in net earnings of subsidiaries									(27.7)	(21.5)		(19.7)
Equity in net earnings (losses) of subsidiaries									72.7	41.3		190.1
Net income									$ 45.0	$ 19.8		$ 170.4

[1] Recast for the adoption of ASU 2018-12. See Note 1 of the Consolidated Financial Statements

[2] Recast for the adoption of ASU 2018-12. See Note 1 of the Consolidated Financial Statements