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Loans - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Loans and Leases Receivable Disclosure [Line Items]        
Uncollectible Portion of Billed Finance Charges and Fees   $ 1,400 $ 1,100 $ 732
Finance Charge And Fees Reserves $ 491 491 402  
Loans held for sale, at lower of cost or fair value 971 971 1,043  
Payments for Origination of Mortgage Loans Held-for-sale   8,400 7,600 $ 6,400
Mortgage loans in process of foreclosure 149 149 382  
Loans and Leases Receivable, Impaired, Commitment to Lend 241 $ 241 $ 208  
Loans Sold Percent Retained Servicing   100.00% 100.00% 100.00%
Performing        
Loans and Leases Receivable Disclosure [Line Items]        
Troubled debt restructurings included in impaired loans 2,200 $ 2,200 $ 2,500  
Home loan | Other Assets        
Loans and Leases Receivable Disclosure [Line Items]        
Real estate acquired through foreclosure 39 39 69  
Consumer Portfolio Segment [Member] | Performing        
Loans and Leases Receivable Disclosure [Line Items]        
Troubled debt restructurings included in impaired loans 1,300 1,300 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 $ 574 574 487  
Consumer Home Loan [Member]        
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 $ 27,300 27,300 29,300  
Line of Credit Facility, Remaining Borrowing Capacity $ 21,000 $ 21,000 $ 24,900