Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Net income	$ 58.4	$ 56.3
Other comprehensive (loss) income, before tax:
Change in net unrealized (losses) gains during the period	(26.4)	78.2
Reclassification adjustment for net losses included in income	0.0	23.4
Reclassification adjustment for securities transferred from held-to-maturity to available-for-sale	0.0	(7.2)
OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax	(0.2)	(0.4)
Change in unrealized (gains) losses on derivatives	(13.9)	10.0
Other comprehensive (loss) income, before tax	(40.5)	104.0
Deferred tax benefit (expense) related to other comprehensive (loss) income	10.1	(26.0)
Other comprehensive (loss) income, net of tax	(30.4)	78.0
Comprehensive income, net of tax	$ 28.0	$ 134.3