Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Statement of Comprehensive Income [Abstract]
Net income	$ 64.1	$ 42.5	$ 30.7	$ 93.9
Other comprehensive (loss) income, before tax:
Change in net unrealized loss during period	(161.6)	(0.8)	(414.2)	(67.6)
Reclassification adjustment for net loss included in income	0.1	0.1	0.2	0.1
Reclassification adjustment for securities transferred from held-to-maturity to available-for-sale	0.0	0.0	0.2	0.0
OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax	(0.9)	24.8	(23.9)	24.8
Change in unrealized (gain) loss on derivatives	(15.0)	(0.8)	6.3	(0.9)
Other comprehensive (loss) income, before tax	(177.4)	23.3	(431.4)	(43.6)
Changes in deferred taxes related to other comprehensive (loss) income	49.6	(5.9)	112.6	11.1
Other comprehensive (loss) income, net of tax	(127.8)	17.4	(318.8)	(32.5)
Comprehensive (loss) income, net of tax	$ (63.7)	$ 59.9	$ (288.1)	$ 61.4