Loans - Loans Classified as TDR Loans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	$ 57	$ 5	$ 159	$ 60
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent				48
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent				48
Commercial Loans [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	57	5	159	12
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent	57	4	159	9
Consumer Loans [Member] | Credit Card Receivables [Member]
Financing Receivable, Modifications [Line Items]
TDR loans during previous months which became contractually delinquent		$ 1		$ 3