Summary of Significant Accounting Policies - Narrative (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($) payment_period Location Segment
Property, Plant and Equipment [Line Items]
Number of client-focused reportable segment | Segment	2
Maximum limit of individual homogeneous loans collective evaluation for impairment and excluded from impaired loan disclosures | $	$ 1,000,000
Lower Limit
Property, Plant and Equipment [Line Items]
Days contractually past due for interest and principal and the loan is not well-secured and in the process of collection	90 days
Loans and leases receivable nonperforming to performing status	6
Restructured loans and leases receivable nonperforming to performing status	6
Period for which troubled debt restructurings with modified terms is performing before ceasing to be classified as impaired loan	6
Troubled debt restructuring loans and leases receivable to Performing status	6
Upper Limit
Property, Plant and Equipment [Line Items]
Number of days past due for disclosure purposes to be categorized as a current	29 days
Buildings | Upper Limit
Property, Plant and Equipment [Line Items]
Charge for depreciation, range of life	30 years
Equipment | Lower Limit
Property, Plant and Equipment [Line Items]
Charge for depreciation, range of life	3 years
Equipment | Upper Limit
Property, Plant and Equipment [Line Items]
Charge for depreciation, range of life	10 years
Leasehold Improvements | Upper Limit
Property, Plant and Equipment [Line Items]
Charge for depreciation, range of life	15 years
WEALTH MANAGEMENT
Property, Plant and Equipment [Line Items]
Minimum assets requirement to be managed | $	$ 200,000,000
Services provided by business units, states | Location	18
Computer Software | Lower Limit
Property, Plant and Equipment [Line Items]
Software, useful life	3 years
Computer Software | Upper Limit
Property, Plant and Equipment [Line Items]
Software, useful life	10 years