Loans - Summary of Nonaccrual Loans and Accruing Receivables 90 Days or More Delinquent (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	$ 1,466		$ 1,629
Total accruing loans contractually past due 90 days or more	40		80
Total nonperforming loans	1,506		1,709
Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	327		463
Total accruing loans contractually past due 90 days or more	5		37
Commercial Loan [Member] | Construction and land loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	47		104
Total accruing loans contractually past due 90 days or more	0		0
Commercial Loan [Member] | Other real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	218		281
Total accruing loans contractually past due 90 days or more	2		8
Commercial Loan [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	30		47
Total accruing loans contractually past due 90 days or more	2		28
Commercial Loan [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	18		18
Total accruing loans contractually past due 90 days or more	0		0
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	14		13
Total accruing loans contractually past due 90 days or more	1		1
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	1,105		1,129
Total accruing loans contractually past due 90 days or more	35		43
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	1,026		1,038
Total accruing loans contractually past due 90 days or more	0		0
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	74		86
Total accruing loans contractually past due 90 days or more	0		0
Consumer Loans [Member] | Total residential mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	1,100	[1]	1,124	[1]
Total accruing loans contractually past due 90 days or more	0		0
Consumer Loans [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total accruing loans contractually past due 90 days or more	13		15
Consumer Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	5		5
Total accruing loans contractually past due 90 days or more	22		28
Nonaccrual Loans Held For Sale [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	$ 34		$ 37

[1] Nonaccrual residential mortgages includes all receivables which are 90 or more days contractually delinquent as well as second lien loans where the first lien loan that we own or service is 90 or more days contractually delinquent.