Loans - Loans Classified as TDR Loans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	$ 11	$ 7	$ 24	$ 13
Commercial Loan [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	0	0	0	0
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	0	0	0	0
Commercial Loan [Member] | Business and Corporate Banking [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	0	0	0	0
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	0	0	0	0
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	11	7	24	13
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	11	7	24	13
Consumer Loans [Member] | Credit Card Receivables [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	$ 0	$ 0	$ 0	$ 0