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Loans - Summary of Receivables which were Modified and as Result Became Classified as TDR Loans (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Commercial Loans [Member]    
Financing Receivable, Impaired [Line Items]    
Loans which were modified and as a result became classified as TDR Loans $ 0 $ 0
Consumer Loans [Member]    
Financing Receivable, Impaired [Line Items]    
Loans which were modified and as a result became classified as TDR Loans 8 9
Consumer Loans [Member] | Residential Mortgage [Member]    
Financing Receivable, Impaired [Line Items]    
Loans which were modified and as a result became classified as TDR Loans 5 6
Consumer Loans [Member] | Home Equity Mortgages [Member]    
Financing Receivable, Impaired [Line Items]    
Loans which were modified and as a result became classified as TDR Loans 2 2
Consumer Loans [Member] | Credit Cards [Member]    
Financing Receivable, Impaired [Line Items]    
Loans which were modified and as a result became classified as TDR Loans $ 1 $ 1