Loans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans in process of foreclosure	$ 505	$ 382
Loans and Leases Receivable, Impaired, Commitment to Lend	271	208
Performing
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructurings included in impaired loans	2,400	2,500
Home loan | Other Assets
Loans and Leases Receivable Disclosure [Line Items]
Real estate acquired through foreclosure	56	69
Consumer Portfolio Segment [Member] | Performing
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructurings included in impaired loans	1,200	1,100
Commercial Banking | Criticized
Loans and Leases Receivable Disclosure [Line Items]
Minimum loan amount reviewed quarterly by management for further deterioration	1
Commercial Banking | Noncriticized
Loans and Leases Receivable Disclosure [Line Items]
Minimum loan amount requiring annual review	1
Commercial Banking | Performing
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructurings included in impaired loans	$ 497	487
Home Loans
Loans and Leases Receivable Disclosure [Line Items]
Threshold Period Past Due for Entering Foreclosure Process Status of Financing Receivables	120 days
Federal Home Loan Bank Advances [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans Pledged as Collateral	$ 27,700	29,300
Line of Credit Facility, Remaining Borrowing Capacity	$ 23,400	$ 24,900