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Allowance for Credit Losses - Summary of Changes in Allowance for Credit Losses and Related Loan Balance by Product - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2017
Dec. 31, 2015
Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]        
Loans $ 73,875 $ 72,563 $ 82,917  
Allowance for credit losses 1,017 681 912 $ 680
TDR loans carried at lower of amortized cost or fair value less cost to sell 672 655 881  
Affiliated Entity [Member]        
Financing Receivable, Allowance for Credit Losses [Line Items]        
Loans 3,274 6,750 4,815  
Commercial Loan [Member]        
Financing Receivable, Allowance for Credit Losses [Line Items]        
Loans 54,216 53,035    
Consumer Loans [Member]        
Financing Receivable, Allowance for Credit Losses [Line Items]        
Loans 19,659 19,528    
Residential Mortgage [Member] | Consumer Loans [Member]        
Financing Receivable, Allowance for Credit Losses [Line Items]        
Loans 17,181 17,273 17,758  
Allowance for credit losses 26 $ 25 $ 68 $ 107
Provision for credit losses and charge-offs related to lower of amortized cost or fair value adjustment attributable to credit factors for loans transferred to held for sale 11      
Additional charge-off for the existing allowance for credit losses on collateral dependent loans transferred to held for sale $ 22