Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 25.6	$ (33.8)
Foreign currency translation:
Foreign currency translation adjustments	(0.1)	0.4
Reclassification adjustment for foreign currency translation included in net income	0.0	0.0
Defined benefit pension plans:
Net gain arising during the period	0.0	1.0
Fixed maturity securities:
Unrealized gains (losses) arising during the period	(13.8)	33.2
Reclassification adjustment for (gains) losses included in net income	(6.5)	22.2
Other comprehensive income (loss) before tax	(20.4)	56.8
Defined benefit pension plans:
Net gain arising during the period	0.0	0.2
Fixed maturity securities:
Unrealized gains (losses) arising during the period	(3.1)	5.2
Reclassification adjustment for (gains) losses included in net income	(1.3)	4.7
Income tax provision (benefit) related to other comprehensive income (loss)	(4.4)	10.1
Other comprehensive income (loss), net of tax	(16.0)	46.7
Comprehensive income (loss)	$ 9.6	$ 12.9