Quality of Loans (Excluding PCI Loans) (Parenthetical) (Detail) - Commercial and Industrial - Taxi Medallion Loans - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 2.0	$ 2.7
Loans 90 Days Or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 43.5	$ 46.7

Recorded Investment in financing receivables that are past due at the balance sheet date.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953401-111524

Name:	us-gaap_FinancingReceivableRecordedInvestmentPastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant