Loans - Summary of Recorded Investments in TDRs by Class of Loan (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) contract	Dec. 31, 2018 USD ($) contract
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	269	208
Pre-Modification Outstanding Recorded Investment	$ 109.3	$ 149.1
Post-Modification Outstanding Recorded Investment	109.3	149.1
Recorded investment	$ 109.3	$ 149.1
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	82	91
Pre-Modification Outstanding Recorded Investment	$ 74.0	$ 132.3
Post-Modification Outstanding Recorded Investment	74.0	132.3
Recorded investment	$ 74.0	$ 132.3
Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	187	117
Pre-Modification Outstanding Recorded Investment	$ 35.3	$ 16.8
Post-Modification Outstanding Recorded Investment	35.3	16.8
Recorded investment	$ 35.3	$ 16.8
Commercial Real Estate Loan [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	12	13
Pre-Modification Outstanding Recorded Investment	$ 17.2	$ 27.6
Post-Modification Outstanding Recorded Investment	17.2	27.6
Recorded investment	$ 17.2	$ 27.6
Commercial Real Estate Loan [Member] | Commercial [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	7	9
Post-Modification Outstanding Recorded Investment	$ 2.1	$ 24.1
Recorded investment	$ 2.1	$ 24.1
Commercial Real Estate Loan [Member] | Commercial [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	1	1
Post-Modification Outstanding Recorded Investment	$ 0.6	$ 0.5
Recorded investment	$ 0.6	$ 0.5
Commercial Real Estate Loan [Member] | Commercial [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	4	3
Post-Modification Outstanding Recorded Investment	$ 14.5	$ 3.0
Recorded investment	$ 14.5	$ 3.0
Commercial and Industrial [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	33	47
Pre-Modification Outstanding Recorded Investment	$ 31.9	$ 73.1
Post-Modification Outstanding Recorded Investment	31.9	73.1
Recorded investment	$ 31.9	$ 73.1
Commercial and Industrial [Member] | Commercial [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	26	31
Post-Modification Outstanding Recorded Investment	$ 26.4	$ 48.4
Recorded investment	$ 26.4	$ 48.4
Commercial and Industrial [Member] | Commercial [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	3	11
Post-Modification Outstanding Recorded Investment	$ 0.8	$ 23.8
Recorded investment	$ 0.8	$ 23.8
Commercial and Industrial [Member] | Commercial [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	4	5
Post-Modification Outstanding Recorded Investment	$ 4.7	$ 0.9
Recorded investment	$ 4.7	$ 0.9
Equipment Financing [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	37	31
Pre-Modification Outstanding Recorded Investment	$ 24.9	$ 31.6
Post-Modification Outstanding Recorded Investment	24.9	31.6
Recorded investment	$ 24.9	$ 31.6
Equipment Financing [Member] | Commercial [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	5	3
Post-Modification Outstanding Recorded Investment	$ 1.6	$ 4.2
Recorded investment	$ 1.6	$ 4.2
Equipment Financing [Member] | Commercial [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	26	16
Post-Modification Outstanding Recorded Investment	$ 18.9	$ 17.6
Recorded investment	$ 18.9	$ 17.6
Equipment Financing [Member] | Commercial [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	6	12
Post-Modification Outstanding Recorded Investment	$ 4.4	$ 9.8
Recorded investment	$ 4.4	$ 9.8
Residential Mortgage Loan [Member] | Commercial [Member] | Foreclosure or Bankruptcy [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		21
Residential Mortgage Loan [Member] | Commercial [Member] | Bankruptcy [Member]
Financing Receivable, Modifications [Line Items]
Post-Modification Outstanding Recorded Investment		$ 3.7
Recorded investment		$ 3.7
Residential Mortgage Loan [Member] | Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	85	38
Pre-Modification Outstanding Recorded Investment	$ 26.3	$ 9.5
Post-Modification Outstanding Recorded Investment	26.3	9.5
Recorded investment	$ 26.3	$ 9.5
Residential Mortgage Loan [Member] | Retail Loans [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	24	10
Post-Modification Outstanding Recorded Investment	$ 10.1	$ 3.5
Recorded investment	$ 10.1	$ 3.5
Residential Mortgage Loan [Member] | Retail Loans [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	16	7
Post-Modification Outstanding Recorded Investment	$ 6.3	$ 2.3
Recorded investment	$ 6.3	$ 2.3
Residential Mortgage Loan [Member] | Retail Loans [Member] | Bankruptcy [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	45
Post-Modification Outstanding Recorded Investment	$ 9.9
Recorded investment	$ 9.9
Home Equity Loan [Member] | Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	102	79
Pre-Modification Outstanding Recorded Investment	$ 9.0	$ 7.3
Post-Modification Outstanding Recorded Investment	9.0	7.3
Recorded investment	$ 9.0	$ 7.3
Home Equity Loan [Member] | Retail Loans [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	18	10
Post-Modification Outstanding Recorded Investment	$ 2.9	$ 1.3
Recorded investment	$ 2.9	$ 1.3
Home Equity Loan [Member] | Retail Loans [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	30	20
Post-Modification Outstanding Recorded Investment	$ 2.9	$ 2.4
Recorded investment	$ 2.9	$ 2.4
Home Equity Loan [Member] | Retail Loans [Member] | Bankruptcy [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	54	49
Post-Modification Outstanding Recorded Investment	$ 3.2	$ 3.6
Recorded investment	$ 3.2	$ 3.6
Other Consumer [Member] | Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	0	0
Pre-Modification Outstanding Recorded Investment	$ 0.0	$ 0.0
Post-Modification Outstanding Recorded Investment	0.0	0.0
Recorded investment	$ 0.0	$ 0.0