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Loans - Summary of TDR and Related Credit Loss Reserves for TDR Loans - Additional Information (Detail) - USD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Other loans included in impaired loans apart from TDR loans $ 164 $ 54  
Residential mortgage loan TDR carried at lower of amortized cost or fair value less cost to sell 557 615 $ 655
Non Accrual loans included in TDR loan 230 286  
Commercial Loans [Member]      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Additional commitments to lend to commercial borrowers with modified TDRs $ 222 $ 151