Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (33.4)	$ 51.4
Other comprehensive (loss) income, before tax:
Change in net unrealized loss during period	(252.6)	(66.8)
Reclassification adjustment for net loss included in income	0.1	0.0
Reclassification adjustment for securities transferred from held-to-maturity to available-for-sale	0.2	0.0
OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax	(23.0)	0.0
Change in unrealized loss (gain) on derivatives	21.3	(0.1)
Other comprehensive loss, before tax	(254.0)	(66.9)
Changes in deferred taxes related to other comprehensive loss	63.0	17.0
Other comprehensive loss, net of tax	(191.0)	(49.9)
Comprehensive (loss) income, net of tax	$ (224.4)	$ 1.5