Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 302.1	$ 226.0	$ 257.5
Other comprehensive income (loss) before tax:
Change in net unrealized losses during period	187.8	48.6	144.8
Comprehensive income, net of tax	445.9	260.6	378.1
Reclassification adjustment for net losses included in net income	0.0	0.0	23.5
Reclassification adjustment for securities transferred from held-to-maturity to available-for-sale	0.0	0.0	(7.2)
OCI, Debt Securities, Available-for-Sale, Transfer to Held-to-Maturity, Adjustment from AOCI for Amortization of Gain (Loss), before Tax	0.2	(0.5)	(1.3)
Change in unrealized gains (losses) on derivatives	1.9	(15.0)	(6.5)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	1.6	12.8	7.4
Other comprehensive income, before tax	191.5	45.9	160.7
Deferred tax expense related to other comprehensive income	(47.7)	(11.3)	(40.1)
Other comprehensive income, net of tax	$ 143.8	$ 34.6	$ 120.6