Loans - Loans Classified as TDR Loans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	$ 16	$ 20
Commercial Loan [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	2	0
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	2	0
Commercial Loan [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	0	0
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	0	0
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	14	20
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	13	19
Consumer Loans [Member] | Credit Card Receivables [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	$ 1	$ 1