Goodwill and Core Deposit Intangibles - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2022	Dec. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
2023	$ 15.6
Finite-lived Intangible Assets [Roll Forward]
Gross other intangible assets, at beginning of the period		$ 106.0	$ 106.0
Provisional amounts established through acquisition	72.9
Finite-Lived Intangible Assets, Period Increase (Decrease)	(1.4)
Accumulated amortization	(76.5)	(64.7)
Net other intangible assets, end of period	101.0	41.3
Core Deposits
Finite-Lived Intangible Assets [Line Items]
2023	13.7
Finite-lived Intangible Assets [Roll Forward]
Gross other intangible assets, at beginning of the period		106.0	106.0
Provisional amounts established through acquisition	50.1
Finite-Lived Intangible Assets, Period Increase (Decrease)	(1.4)
Accumulated amortization	(75.2)	(64.7)
Net other intangible assets, end of period	79.5	41.3
OCRI
Finite-Lived Intangible Assets [Line Items]
2023	1.9
Finite-lived Intangible Assets [Roll Forward]
Gross other intangible assets, at beginning of the period		0.0	$ 0.0
Provisional amounts established through acquisition	22.8
Finite-Lived Intangible Assets, Period Increase (Decrease)	0.0
Accumulated amortization	(1.3)	0.0
Net other intangible assets, end of period	$ 21.5	$ 0.0