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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
Mar. 31, 2018
Dec. 31, 2017
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment $ 4,812 $ 5,027
Unpaid Principal Balance 5,753 6,205
Valuation Allowance 270 279
Commitments to Lend Additional Funds 219 204
Commercial [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 540 550
Unpaid Principal Balance 833 915
Valuation Allowance 42 44
Commitments to Lend Additional Funds 214 199
Commercial Real Estate [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 254 280
Unpaid Principal Balance 573 596
Valuation Allowance 9 11
Residential Mortgages [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 1,881 1,946
Unpaid Principal Balance 2,118 2,339
Valuation Allowance 109 116
Commitments to Lend Additional Funds 1 1
Other Retail [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 299 302
Unpaid Principal Balance 383 400
Valuation Allowance 19 22
Commitments to Lend Additional Funds 4 4
Credit Card [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 234 230
Unpaid Principal Balance 234 230
Valuation Allowance 60 60
Total Loans, Excluding GNMA and Covered Loans [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 3,208 3,308
Unpaid Principal Balance 4,141 4,480
Valuation Allowance 239 253
Commitments to Lend Additional Funds 219 204
Covered Loans [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 38 38
Unpaid Principal Balance 46 44
Valuation Allowance 1 1
Government National Mortgage Association [Member]    
Financing Receivable, Impaired [Line Items]    
Period-end Recorded Investment 1,566 1,681
Unpaid Principal Balance 1,566 1,681
Valuation Allowance $ 30 $ 25