Loans - Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Loans held for sale, at lower of cost or fair value	$ 905	$ 1,192
Loans and Leases Receivable, Impaired, Commitment to Lend	232	256
Performing
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructurings included in impaired loans	1,700	1,600
Federal Home Loan banks
Loans and Leases Receivable Disclosure [Line Items]
Loans Pledged as Collateral	15,300	15,800
Line of Credit Facility, Remaining Borrowing Capacity	18,800	19,300
Federal Reserve Discount Window
Loans and Leases Receivable Disclosure [Line Items]
Loans Pledged as Collateral	8,400	9,200
Line of Credit Facility, Remaining Borrowing Capacity	7,000	7,600
Consumer Banking | Performing
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructurings included in impaired loans	1,200	1,200
Commercial Banking | Performing
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructurings included in impaired loans	$ 300	$ 282