Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 56.3	$ (33.4)
Other comprehensive income (loss), before tax:
Change in net unrealized gains (losses) during the period	78.2	(252.6)
Reclassification adjustment for net losses included in income	23.4	0.1
Reclassification adjustment for securities transferred from held-to-maturity to available-for-sale	(7.2)	0.2
OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax	(0.4)	(23.0)
Change in unrealized loss on derivatives	10.0	21.3
Other comprehensive income (loss), before tax	104.0	(254.0)
Deferred tax (expense) benefit related to other comprehensive income (loss)	(26.0)	63.0
Other comprehensive income (loss), net of tax	78.0	(191.0)
Comprehensive income (loss), net of tax	$ 134.3	$ (224.4)