Loans - Loans Classified as TDR Loans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during the previous 12 months which became contractually delinquent	$ 10	$ 40	$ 39	$ 65
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during the previous 12 months which became contractually delinquent	0	30	12	30
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during the previous 12 months which became contractually delinquent	0	28	12	28
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during the previous 12 months which became contractually delinquent	0	2	0	2
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during the previous 12 months which became contractually delinquent	10	10	27	35
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during the previous 12 months which became contractually delinquent	10	10	27	34
Consumer Loans [Member] | Home Equity Line of Credit [Member]
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during the previous 12 months which became contractually delinquent	$ 0	$ 0	$ 0	$ 1