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Loans and Allowance for Credit Losses - Summary of Impaired Loans, which Include Nonaccrual and TDR Loans, by Portfolio Class (Detail) - USD ($)
$ in Millions
Sep. 30, 2017
Dec. 31, 2016
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment $ 5,054 $ 5,529
Unpaid Principal Balance 6,409 7,202
Valuation Allowance 273 346
Commitments to Lend Additional Funds 173 289
Commercial [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 592 849
Unpaid Principal Balance 1,040 1,364
Valuation Allowance 39 68
Commitments to Lend Additional Funds 168 284
Commercial Real Estate [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 263 293
Unpaid Principal Balance 545 697
Valuation Allowance 11 10
Residential Mortgages [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 2,064 2,274
Unpaid Principal Balance 2,471 2,847
Valuation Allowance 121 153
Commitments to Lend Additional Funds 1  
Other Retail [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 298 281
Unpaid Principal Balance 508 456
Valuation Allowance 19 22
Commitments to Lend Additional Funds 4 4
Credit Card [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 231 222
Unpaid Principal Balance 231 222
Valuation Allowance 62 64
Total Loans, Excluding GNMA and Covered Loans [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 3,448 3,919
Unpaid Principal Balance 4,795 5,586
Valuation Allowance 252 317
Commitments to Lend Additional Funds 173 288
Covered Loans [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 35 36
Unpaid Principal Balance 43 42
Valuation Allowance 1 1
Commitments to Lend Additional Funds   1
Government National Mortgage Association [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 1,571 1,574
Unpaid Principal Balance 1,571 1,574
Valuation Allowance $ 20 $ 28