Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 51.4	$ 29.3
Other comprehensive (loss) income, before tax:
Change in net unrealized (losses) gains during period	(66.8)	39.2
Unrealized gain on derivatives	(0.1)	0.0
Change in net actuarial loss	0.0	0.2
Other comprehensive (loss) income, before tax	(66.9)	39.0
Changes in deferred taxes related to other comprehensive loss (income)	17.0	(10.2)
Other comprehensive (loss) income, net of tax	(49.9)	28.8
Comprehensive income, net of tax	$ 1.5	$ 58.1