Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (175.2)	$ 6.7	$ (54.1)
Foreign currency translation:
Foreign currency translation adjustments	(0.7)	2.6	(15.3)
Reclassification adjustment for foreign currency translation included in net income	31.8	0.0	0.0
Defined benefit pension plans:
Net gain (loss) arising during the year	(0.9)	1.9	(0.6)
Unrealized losses on fixed maturity securities:
(Losses) gains arising during the year	(428.1)	(94.7)	95.2
Reclassification adjustment for losses (gains) included in net income	43.6	(12.2)	(12.8)
Other comprehensive (loss) income before tax	(354.3)	(102.4)	66.5
Defined benefit pension plans:
Net gain (loss) arising during the year	(0.2)	0.4	(0.1)
Unrealized gains (losses) on fixed maturity securities:
(Losses) gains arising during the year	(80.9)	(17.3)	16.5
Reclassification adjustment for losses (gains) included in net income (loss)	9.2	(4.2)	0.0
Income tax (benefit) provision related to other comprehensive income (loss)	(71.9)	(21.1)	16.4
Other comprehensive (loss) income, net of tax	(282.4)	(81.3)	50.1
Comprehensive (loss) income	$ (457.6)	$ (74.6)	$ (4.0)