Loans, Leases and Allowance for Credit Losses - Allowances for Credit Losses (Detail) Valuation - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Valuation Allowance [Line Items]
Provision for Loan and Lease Losses	$ (20.5)	$ (106.5)
Financing Receivable, Allowance for Credit Loss, Writeoff	11.6	20.4
Financing Receivable, Allowance for Credit Loss, Recovery	(5.7)	(5.9)
Financing Receivable, Collectively Evaluated for Impairment	38,812.3	26,787.4
Financing Receivable, Individually Evaluated for Impairment	(263.1)	(265.6)
Loans and Leases Receivable, Net of Deferred Income	39,075.4	27,053.0
Loans and Leases Receivable, Allowance	252.5	278.9
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	236.4	267.7
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	16.1	11.2
Financing Receivable, Allowance for Credit Loss	252.5	278.9	$ 186.9
Off-Balance Sheet, Credit Loss, Liability	37.6	37.0		$ 9.0
Off-Balance Sheet, Credit Loss, Liability, Change in Method, Credit Loss Expense (Reversal)	0.6	12.9
Interest Receivable	197.6	142.1
Cumulative Effect, Period of Adoption, Adjustment [Member]
Valuation Allowance [Line Items]
Off-Balance Sheet, Credit Loss, Liability			15.1
Tech & Innovation [Member]
Valuation Allowance [Line Items]
Provision for Loan and Lease Losses	(6.2)	(23.5)
Financing Receivable, Allowance for Credit Loss, Writeoff	2.0	11.1
Financing Receivable, Allowance for Credit Loss, Recovery	(0.5)	0.0
Financing Receivable, Collectively Evaluated for Impairment	1,400.8	1,375.8
Financing Receivable, Individually Evaluated for Impairment	(17.0)	(27.2)
Loans and Leases Receivable, Net of Deferred Income	1,417.8	1,403.0
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	22.9	29.5
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2.8	3.9
Financing Receivable, Allowance for Credit Loss	25.7	33.4	21.0
Other commercial and industrial [Member]
Valuation Allowance [Line Items]
Provision for Loan and Lease Losses	(14.0)	(1.8)
Financing Receivable, Allowance for Credit Loss, Writeoff	7.4	6.4
Financing Receivable, Allowance for Credit Loss, Recovery	(2.3)	(3.5)
Financing Receivable, Collectively Evaluated for Impairment	6,442.7	5,883.1
Financing Receivable, Individually Evaluated for Impairment	(23.0)	(28.1)
Loans and Leases Receivable, Net of Deferred Income	6,465.7	5,911.2
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	101.1	90.3
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2.5	4.4
Financing Receivable, Allowance for Credit Loss	103.6	94.7	95.8
Commercial Real Estate Owner Occupied [Member]
Valuation Allowance [Line Items]
Provision for Loan and Lease Losses	(8.0)	(8.3)
Financing Receivable, Allowance for Credit Loss, Writeoff	0.0	0.2
Financing Receivable, Allowance for Credit Loss, Recovery	0.0	(0.1)
Financing Receivable, Collectively Evaluated for Impairment	1,699.3	1,857.9
Financing Receivable, Individually Evaluated for Impairment	(24.4)	(51.4)
Loans and Leases Receivable, Net of Deferred Income	1,723.7	1,909.3
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	10.6	18.6
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0.0	0.0
Financing Receivable, Allowance for Credit Loss	10.6	18.6	10.4
Hotel franchise finance [Member]
Valuation Allowance [Line Items]
Provision for Loan and Lease Losses	(2.1)	(29.2)
Financing Receivable, Allowance for Credit Loss, Writeoff	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Recovery	(0.3)	0.0
Financing Receivable, Collectively Evaluated for Impairment	2,378.3	1,927.0
Financing Receivable, Individually Evaluated for Impairment	(155.7)	(56.9)
Loans and Leases Receivable, Net of Deferred Income	2,534.0	1,983.9
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	30.7	40.4
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	10.8	2.9
Financing Receivable, Allowance for Credit Loss	41.5	43.3	14.1
Other Commercial Real Estate Non owner Occupied [Member]
Valuation Allowance [Line Items]
Provision for Loan and Lease Losses	(22.5)	(29.8)
Financing Receivable, Allowance for Credit Loss, Writeoff	2.0	2.1
Financing Receivable, Allowance for Credit Loss, Recovery	(1.5)	(1.7)
Financing Receivable, Collectively Evaluated for Impairment	3,917.3	3,553.6
Financing Receivable, Individually Evaluated for Impairment	(34.5)	(86.6)
Loans and Leases Receivable, Net of Deferred Income	3,951.8	3,640.2
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	16.9	39.9
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0.0	0.0
Financing Receivable, Allowance for Credit Loss	16.9	39.9	10.5
Residential Real Estate [Member]
Valuation Allowance [Line Items]
Provision for Loan and Lease Losses	(11.2)	(3.1)
Financing Receivable, Allowance for Credit Loss, Writeoff	0.0	0.3
Financing Receivable, Allowance for Credit Loss, Recovery	(0.5)	(0.4)
Financing Receivable, Collectively Evaluated for Impairment	9,242.8	2,367.1
Financing Receivable, Individually Evaluated for Impairment	0.0	(11.4)
Loans and Leases Receivable, Net of Deferred Income	9,242.8	2,378.5
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	12.5	0.8
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0.0	0.0
Financing Receivable, Allowance for Credit Loss	12.5	0.8	3.8
Construction and land development [Member]
Valuation Allowance [Line Items]
Provision for Loan and Lease Losses	(9.5)	(15.7)
Financing Receivable, Allowance for Credit Loss, Writeoff	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Recovery	0.0	(0.1)
Financing Receivable, Collectively Evaluated for Impairment	2,997.6	2,427.9
Financing Receivable, Individually Evaluated for Impairment	(8.2)	(1.5)
Loans and Leases Receivable, Net of Deferred Income	3,005.8	2,429.4
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	12.5	22.0
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0.0	0.0
Financing Receivable, Allowance for Credit Loss	12.5	22.0	6.2
Warehouse lending [Member]
Valuation Allowance [Line Items]
Provision for Loan and Lease Losses	(0.4)	(3.2)
Financing Receivable, Allowance for Credit Loss, Writeoff	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Recovery	0.0	0.0
Financing Receivable, Collectively Evaluated for Impairment	5,155.9	4,340.2
Financing Receivable, Individually Evaluated for Impairment	0.0	0.0
Loans and Leases Receivable, Net of Deferred Income	5,155.9	4,340.2
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3.0	3.4
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0.0	0.0
Financing Receivable, Allowance for Credit Loss	3.0	3.4	0.2
Municipal and nonprofit [Member]
Valuation Allowance [Line Items]
Provision for Loan and Lease Losses	(2.2)	(1.5)
Financing Receivable, Allowance for Credit Loss, Writeoff	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Recovery	0.0	0.0
Financing Receivable, Collectively Evaluated for Impairment	1,579.2	1,726.9
Financing Receivable, Individually Evaluated for Impairment	0.0	(1.9)
Loans and Leases Receivable, Net of Deferred Income	1,579.2	1,728.8
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	13.7	15.9
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0.0	0.0
Financing Receivable, Allowance for Credit Loss	13.7	15.9	17.4
Other, loan segment [Member]
Valuation Allowance [Line Items]
Provision for Loan and Lease Losses	(2.5)	(0.9)
Financing Receivable, Allowance for Credit Loss, Writeoff	0.2	0.3
Financing Receivable, Allowance for Credit Loss, Recovery	(0.6)	(0.1)
Financing Receivable, Collectively Evaluated for Impairment	168.6	182.6
Financing Receivable, Individually Evaluated for Impairment	(0.3)	(0.6)
Loans and Leases Receivable, Net of Deferred Income	168.9	183.2
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2.9	5.0
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0.0	0.0
Financing Receivable, Allowance for Credit Loss	2.9	5.0	6.1
Equity fund resources
Valuation Allowance [Line Items]
Provision for Loan and Lease Losses	(7.7)	(0.5)
Financing Receivable, Allowance for Credit Loss, Writeoff	0.0	0.0
Financing Receivable, Allowance for Credit Loss, Recovery	0.0	0.0
Financing Receivable, Collectively Evaluated for Impairment	3,829.8	1,145.3
Financing Receivable, Individually Evaluated for Impairment	0.0	0.0
Loans and Leases Receivable, Net of Deferred Income	3,829.8	1,145.3
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	9.6	1.9
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0.0	0.0
Financing Receivable, Allowance for Credit Loss	$ 9.6	$ 1.9	$ 1.4