Loans - Loans Classified as TDR Loans (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during the previous 12 months which became contractually delinquent	$ 48	$ 58
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans which were classified as TDR loans during the previous 12 months which became contractually delinquent	14	14
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	12	12
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	2	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	34	44
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	34	43
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	$ 1