Loans - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Loans held for sale, at lower of cost or fair value	$ 1,245	$ 1,192
Financing Receivable, Troubled Debt Restructuring, Commitment to Lend	220	256
Performing
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructurings included in impaired loans	1,600	1,600
Federal Home Loan banks
Loans and Leases Receivable Disclosure [Line Items]
Loans Pledged as Collateral	14,400	15,800
Line of Credit Facility, Remaining Borrowing Capacity	19,200	19,300
Federal Reserve Discount Window
Loans and Leases Receivable Disclosure [Line Items]
Loans Pledged as Collateral	7,200	9,200
Line of Credit Facility, Remaining Borrowing Capacity	5,800	7,600
Consumer Banking | Performing
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructurings included in impaired loans	1,100	1,200
Commercial Banking | Performing
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructurings included in impaired loans	$ 276	$ 282