Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Statement of Comprehensive Income [Abstract]
Net income	$ 83.9	$ 71.7	$ 144.1	$ 121.9
Other comprehensive income, before tax:
(Increase) decrease in unrealized losses during the period	(10.4)	44.7	(33.9)	115.4
OCI, Debt Securities, Available-for-Sale, Transfer to Held-to-Maturity, Adjustment from AOCI for Amortization of Gain (Loss), before Tax	0.1	(0.1)	0.2	(0.1)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax	0.0	0.9	0.0	1.9
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	(0.1)	0.4	(0.1)	1.4
Deferred tax benefit (expense) related to other comprehensive income	2.6	(11.3)	8.4	(29.6)
Other comprehensive (loss) income, net of tax	(7.8)	34.6	(25.4)	89.0
Other comprehensive (loss) income, before tax	(10.4)	45.9	(33.8)	118.6
Comprehensive income, net of tax	$ 76.1	$ 106.3	$ 118.7	$ 210.9