Loans - Schedule of Impaired Financing Receivable (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	$ 202.4	$ 217.8	$ 256.6
Interest Income Recognized	5.7	6.4	5.6
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	111.1	128.2	163.6
Interest Income Recognized	3.0	4.0	3.5
Commercial [Member] \| Commercial Real Estate Loan [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	39.6	40.2	55.8
Interest Income Recognized	1.1	1.1	1.2
Commercial [Member] \| Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	44.5	49.6	63.4
Interest Income Recognized	1.6	2.8	1.9
Commercial [Member] \| Equipment Financing [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	27.0	38.4	44.4
Interest Income Recognized	0.3	0.1	0.4
Retail Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	91.3	89.6	93.0
Interest Income Recognized	2.7	2.4	2.1
Retail Loans [Member] \| Residential Mortgage Loan [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	68.3	68.7	71.8
Interest Income Recognized	2.1	1.9	1.7
Retail Loans [Member] \| Home Equity Loan [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	23.0	20.9	21.2
Interest Income Recognized	0.6	0.5	0.4
Retail Loans [Member] \| Other Consumer [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	0.0	0.0	0.0
Interest Income Recognized	$ 0.0	$ 0.0	$ 0.0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5258-111524

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Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

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