Loans - Summary of Nonaccrual Loans and Accruing Receivables 90 Days or More Delinquent (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	$ 1,790	$ 1,828
Total accruing loans contractually past due 90 days or more	51	61
Total nonperforming loans	1,841	1,889
Nonaccrual loans held for sale [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	51	91
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	658	825
Total accruing loans contractually past due 90 days or more	9	14
Commercial Loans [Member] | Construction and land loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	98	103
Commercial Loans [Member] | Other real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	353	512
Total accruing loans contractually past due 90 days or more	1	1
Commercial Loans [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	46	58
Total accruing loans contractually past due 90 days or more	7	11
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	142	137
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	19	15
Total accruing loans contractually past due 90 days or more	1	2
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	1,081	912
Total accruing loans contractually past due 90 days or more	42	47
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	979	815
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	97	89
Consumer Loans [Member] | Total residential mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	1,076	904
Consumer Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	5	8
Total accruing loans contractually past due 90 days or more	27	27
Consumer Loans [Member] | Credit Card Receivables [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total accruing loans contractually past due 90 days or more	$ 15	$ 20