Other Comprehensive Income/Loss - Schedule of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Jun. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total stockholders’ equity	$ 3,160.3	$ 3,441.1		$ 3,073.8	$ 1,986.6
Net unrealized gain (loss) on derivatives	7.5	16.0
Change in net unrealized gain during period, pre-tax	78.2	(252.6)
Change in net unrealized gain during period, tax expense (benefit)	19.6	(62.7)
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	58.6	(189.9)
Reclassification adjustment for net losses included in income	23.4	0.1
Reclassification adjustment for net gains included in income, tax expense (benefit)	5.8	0.0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	17.6	0.1
OCI, Debt Securities, Available-for-Sale, Transfer to Held-to-Maturity, Adjustment from AOCI for Amortization of Gain (Loss), before Tax	(0.4)	(23.0)
Amortization of unrealized gains on available-for-sale securities transferred into held-to-maturity, tax expense (benefit)	(0.1)	(5.7)
OCI, Debt Securities, Available-for-Sale, Transfer to Held-to-Maturity, Adjustment from AOCI for Amortization of Gain (Loss), after Tax	(0.3)	(17.3)
Unrealized loss on derivatives, pre-tax	10.0	21.3
Unrealized loss on derivatives, tax expense (benefit)	2.5	5.3
Other comprehensive income (loss), before tax	104.0	(254.0)
Other Comprehensive Income (Loss), tax expense (benefit)	26.0	(63.0)
Other Comprehensive Income (Loss), Net of Tax	78.0	(191.0)
Net unrealized loss on investment securities available-for-sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total stockholders’ equity	(400.2)			(471.0)
OCI, Debt Securities, Available-for-Sale, Transfer from Held-to-Maturity, Gain (Loss), before Adjustment, after Tax	(4.9)		$ (4.5)
Net unrealized gain (loss) on derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized gain (loss) on derivatives	6.0		$ (1.6)
Net accumulated other comprehensive loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total stockholders’ equity	$ (399.1)	$ (202.0)		$ (477.1)	$ (11.0)