Loans - Loans Classified as TDR Loans (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during previous 12 months which became contractually delinquent	$ 6	$ 14	$ 25	$ 36
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during previous 12 months which became contractually delinquent	$ 0	$ 7	$ 4	$ 12
Threshold period for troubled debt restructuring status	90 days	90 days	90 days	90 days
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during previous 12 months which became contractually delinquent	$ 0	$ 0	$ 0	$ 2
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during previous 12 months which became contractually delinquent	0	7	4	10
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during previous 12 months which became contractually delinquent	$ 6	$ 7	$ 21	$ 24
Threshold period for troubled debt restructuring status	60 days	60 days	60 days	60 days
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during previous 12 months which became contractually delinquent	$ 6	$ 6	$ 21	$ 23
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during previous 12 months which became contractually delinquent	$ 0	$ 1	$ 0	$ 1