Other Assets - Software, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Capitalized internal-use software, accumulated amortization	$ 39.8	$ 43.6
Capitalized internal-use software, net book value	15.1	13.3
Hosting arrangements
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Capitalized internal-use software, accumulated amortization	7.7	0.6
Capitalized internal-use software, net book value	110.5	77.7
Other noninterest expense
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Amortization expense for all capitalized implementation costs	5.4	8.6	$ 6.4
Equipment expense | Hosting arrangements
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Amortization expense for all capitalized implementation costs	7.2	0.5	$ 0.1
Included in other assets
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total capitalized internal-use software	54.9	56.9
Included in other assets | Hosting arrangements
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total capitalized internal-use software	$ 118.2	$ 78.3