Loans, Leases and Allowance for Credit Losses - Schedule of Held for Investment Loan Portfolio Composition of Loans, Leases and Allowance for Credit Losses (Detail) - USD ($) $ in Millions	Jun. 30, 2026	Mar. 31, 2026	Dec. 31, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	$ 60,949.0		$ 58,677.0
Less: allowance for credit losses	(487.4)	$ (461.1)	(460.6)	$ (394.7)	$ (388.6)	$ (373.8)
Net loans HFI	60,462.0		58,216.0
Mortgage finance
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	7,405.0		7,271.0
Less: allowance for credit losses	(6.1)	(5.7)	(5.5)	(4.4)	(4.5)	(4.8)
Municipal & nonprofit
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	1,716.0		1,648.0
Less: allowance for credit losses	(15.7)	(18.4)	(13.0)	(11.3)	(14.8)	(14.7)
Tech & innovation
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	4,488.0		4,128.0
Less: allowance for credit losses	(52.2)	(52.9)	(44.8)	(45.7)	(44.9)	(55.9)
Equity fund resources
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	1,457.0		1,233.0
Less: allowance for credit losses	(4.7)	(4.0)	(2.6)	(2.2)	(1.4)	(1.6)
Other commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	14,951.0		13,789.0
Less: allowance for credit losses	(176.7)	(174.0)	(184.7)	(110.7)	(93.5)	(79.4)
CRE - owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	1,469.0		1,533.0
Less: allowance for credit losses	(3.1)	(3.6)	(3.4)	(3.9)	(3.7)	(3.4)
Hotel franchise finance
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	4,582.0		4,185.0
Less: allowance for credit losses	(42.5)	(40.5)	(37.7)	(36.0)	(33.2)	(35.3)
Other CRE - non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	5,969.0		6,455.0
Less: allowance for credit losses	(125.6)	(99.4)	(110.4)	(125.0)	(138.1)	(134.4)
Residential
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	13,909.0		13,403.0
Less: allowance for credit losses	(23.1)	(23.7)	(23.7)	(19.9)	(19.7)	(19.7)
Residential EBO
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	752.0		828.0
Less: allowance for credit losses	0.0	0.0	0.0	0.0	0.0	0.0
Construction and land development
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	4,072.0		4,043.0
Less: allowance for credit losses	(35.4)	(37.6)	(32.3)	(33.6)	(32.0)	(21.3)
Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans HFI, net of deferred fees and costs	179.0		161.0
Less: allowance for credit losses	$ (2.3)	$ (1.3)	$ (2.5)	$ (2.0)	$ (2.8)	$ (3.3)