Credit Quality (Summary of Portfolio Loans, by Class, that Received Payment Deferrals or Forbearances) (Detail) - COVID-19 Hardship Relief Programs $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) Loans
Financing Receivable, Impaired [Line Items]
Number of Loans Placed into Programs | Loans	14,714
Principal Balance of Loans Placed into Programs	$ 627
30 to 89 days past due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	36
90 Days and Greater Past Due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	$ 36
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Impaired [Line Items]
Number of Loans Placed into Programs | Loans	402
Principal Balance of Loans Placed into Programs	$ 40
Commercial Portfolio Segment | Commercial and Industrial Loans | 30 to 89 days past due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	0
Commercial Portfolio Segment | Commercial and Industrial Loans | 90 Days and Greater Past Due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	$ 0
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-Occupied
Financing Receivable, Impaired [Line Items]
Number of Loans Placed into Programs | Loans	1
Principal Balance of Loans Placed into Programs	$ 0
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-Occupied | 30 to 89 days past due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	0
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-Occupied | 90 Days and Greater Past Due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	$ 0
Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Impaired [Line Items]
Number of Loans Placed into Programs | Loans	69
Principal Balance of Loans Placed into Programs	$ 32
Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied | 30 to 89 days past due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	0
Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied | 90 Days and Greater Past Due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	$ 0
Residential Mortgage Loans
Financing Receivable, Impaired [Line Items]
Number of Loans Placed into Programs | Loans	1,592
Principal Balance of Loans Placed into Programs	$ 361
Residential Mortgage Loans | 30 to 89 days past due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	32
Residential Mortgage Loans | 90 Days and Greater Past Due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	$ 35
Consumer Portfolio Segment | Home Equity
Financing Receivable, Impaired [Line Items]
Number of Loans Placed into Programs | Loans	240
Principal Balance of Loans Placed into Programs	$ 22
Consumer Portfolio Segment | Home Equity | 30 to 89 days past due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	0
Consumer Portfolio Segment | Home Equity | 90 Days and Greater Past Due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	$ 0
Consumer Portfolio Segment | Indirect secured consumer loans
Financing Receivable, Impaired [Line Items]
Number of Loans Placed into Programs | Loans	5,384
Principal Balance of Loans Placed into Programs	$ 114
Consumer Portfolio Segment | Indirect secured consumer loans | 30 to 89 days past due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	0
Consumer Portfolio Segment | Indirect secured consumer loans | 90 Days and Greater Past Due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	$ 0
Consumer Portfolio Segment | Credit Card
Financing Receivable, Impaired [Line Items]
Number of Loans Placed into Programs | Loans	4,673
Principal Balance of Loans Placed into Programs	$ 28
Consumer Portfolio Segment | Credit Card | 30 to 89 days past due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	3
Consumer Portfolio Segment | Credit Card | 90 Days and Greater Past Due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	$ 1
Consumer Portfolio Segment | Other Consumer Loans
Financing Receivable, Impaired [Line Items]
Number of Loans Placed into Programs | Loans	2,353
Principal Balance of Loans Placed into Programs	$ 30
Consumer Portfolio Segment | Other Consumer Loans | 30 to 89 days past due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	1
Consumer Portfolio Segment | Other Consumer Loans | 90 Days and Greater Past Due
Financing Receivable, Impaired [Line Items]
Balances of Accounts that were Past Due Prior to Placement into Programs	$ 0