CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (132.3)	$ (46.9)	$ (94.0)	$ (78.5)
Foreign currency translation:
Foreign currency translation adjustments	0.4	0.5	0.3	1.0
Defined benefit pension plans:
Net gain arising during the period	0.0	0.0	0.0	1.0
Fixed maturity securities:
Unrealized gains (losses) arising during the period	50.9	(20.7)	25.7	(0.7)
Reclassification adjustment for losses (gains) included in net income (loss)	1.6	1.5	(4.8)	27.4
Other comprehensive income (loss) before tax	52.9	(18.7)	21.2	28.7
Defined benefit pension plans:
Net gain arising during the period	0.0	0.0	0.0	0.2
Fixed maturity securities:
Unrealized gains (losses) arising during the period	10.9	(3.3)	5.4	(0.3)
Reclassification adjustment for losses (gains) included in net income	0.3	(0.4)	(1.0)	5.0
Income tax provision (benefit) related to other comprehensive income (loss)	11.2	(3.7)	4.4	4.9
Other comprehensive income (loss), net of tax	41.7	(15.0)	16.8	23.8
Comprehensive income (loss)	$ (90.6)	$ (61.9)	$ (77.2)	$ (54.7)