Loans - Summary of Aging Information by Class of Loan (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 43,596.1	$ 35,241.4
Originated [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	32,501.7	30,420.8
Past Due	233.7	229.2
Total loans	32,735.4	30,650.0
Originated [Member] | 30-89 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	149.8	143.2
Originated [Member] | 90 Days or More [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	83.9	86.0
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	30,714.3	25,077.7
Commercial [Member] | Commercial Real Estate Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	14,762.3	11,649.6
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	11,041.6	9,088.9
Commercial [Member] | Equipment Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	4,910.4	4,339.2
Commercial [Member] | Originated [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	24,312.9	21,878.9
Past Due	168.8	149.6
Total loans	24,481.7	22,028.5
Commercial [Member] | Originated [Member] | Commercial Real Estate Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	9,983.5	9,762.1
Past Due	29.0	36.4
Total loans	10,012.5	9,798.5
Commercial [Member] | Originated [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	9,738.0	8,261.5
Past Due	25.1	30.8
Total loans	9,763.1	8,292.3
Commercial [Member] | Originated [Member] | Equipment Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	4,591.4	3,855.3
Past Due	114.7	82.4
Total loans	4,706.1	3,937.7
Commercial [Member] | Originated [Member] | 30-89 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	113.0	98.7
Commercial [Member] | Originated [Member] | 30-89 Days [Member] | Commercial Real Estate Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	7.8	23.0
Commercial [Member] | Originated [Member] | 30-89 Days [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	10.5	6.9
Commercial [Member] | Originated [Member] | 30-89 Days [Member] | Equipment Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	94.7	68.8
Commercial [Member] | Originated [Member] | 90 Days or More [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	55.8	50.9
Commercial [Member] | Originated [Member] | 90 Days or More [Member] | Commercial Real Estate Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	21.2	13.4
Commercial [Member] | Originated [Member] | 90 Days or More [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	14.6	23.9
Commercial [Member] | Originated [Member] | 90 Days or More [Member] | Equipment Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	20.0	13.6
Retail Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	12,881.8	10,163.7
Retail Loans [Member] | Residential Mortgage Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	10,318.1	8,154.2
Retail Loans [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,406.5	1,962.5
Retail Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	157.2	47.0
Retail Loans [Member] | Originated [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	8,188.8	8,541.9
Past Due	64.9	79.6
Total loans	8,253.7	8,621.5
Retail Loans [Member] | Originated [Member] | Residential Mortgage Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	6,534.3	6,723.2
Past Due	54.6	66.0
Total loans	6,588.9	6,789.2
Retail Loans [Member] | Originated [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,615.0	1,776.0
Past Due	10.1	13.5
Total loans	1,625.1	1,789.5
Retail Loans [Member] | Originated [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	39.5	42.7
Past Due	0.2	0.1
Total loans	39.7	42.8
Retail Loans [Member] | Originated [Member] | 30-89 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	36.8	44.5
Retail Loans [Member] | Originated [Member] | 30-89 Days [Member] | Residential Mortgage Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	31.6	38.6
Retail Loans [Member] | Originated [Member] | 30-89 Days [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	5.0	5.8
Retail Loans [Member] | Originated [Member] | 30-89 Days [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0.2	0.1
Retail Loans [Member] | Originated [Member] | 90 Days or More [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	28.1	35.1
Retail Loans [Member] | Originated [Member] | 90 Days or More [Member] | Residential Mortgage Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	23.0	27.4
Retail Loans [Member] | Originated [Member] | 90 Days or More [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	5.1	7.7
Retail Loans [Member] | Originated [Member] | 90 Days or More [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 0.0	$ 0.0