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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
Dec. 31, 2017
Dec. 31, 2016
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment $ 5,027 $ 5,529
Unpaid Principal Balance 6,205 7,202
Valuation Allowance 279 346
Commitments to Lend Additional Funds 204 289
Commercial [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 550 849
Unpaid Principal Balance 915 1,364
Valuation Allowance 44 68
Commitments to Lend Additional Funds 199 284
Commercial Real Estate [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 280 293
Unpaid Principal Balance 596 697
Valuation Allowance 11 10
Residential Mortgages [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 1,946 2,274
Unpaid Principal Balance 2,339 2,847
Valuation Allowance 116 153
Commitments to Lend Additional Funds 1  
Other Retail [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 302 281
Unpaid Principal Balance 400 456
Valuation Allowance 22 22
Commitments to Lend Additional Funds 4 4
Credit Card [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 230 222
Unpaid Principal Balance 230 222
Valuation Allowance 60 64
Total Loans, Excluding GNMA and Covered Loans [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 3,308 3,919
Unpaid Principal Balance 4,480 5,586
Valuation Allowance 253 317
Commitments to Lend Additional Funds 204 288
Covered Loans [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 38 36
Unpaid Principal Balance 44 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 1,681 1,574
Unpaid Principal Balance 1,681 1,574
Valuation Allowance $ 25 $ 28