Credit Quality (Summary of Transactions in the ALLL by Portfolio Segment) (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, allowance changes due to adoption of accounting standards	$ 13	$ (3)
Losses charged-off	159	108
Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Losses charged-off	61	20
Commercial Portfolio Segment | Financial Asset Acquired with Credit Deterioration
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, allowance changes due to adoption of accounting standards	31
Residential Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Losses charged-off	2	2
Residential Portfolio Segment | Financial Asset Acquired with Credit Deterioration
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, allowance changes due to adoption of accounting standards	1
Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Losses charged-off	96	86
Consumer Portfolio Segment | Financial Asset Acquired with Credit Deterioration
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, allowance changes due to adoption of accounting standards	1
Other Consumer Loans, Point of Sale
Financing Receivable, Allowance for Credit Loss [Line Items]
Losses charged-off	$ 13	$ 11