Loans - Summary of Nonaccrual Loans and Accruing Receivables 90 Days or More Delinquent (Detail) (USD $)	Sep. 30, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	$ 1,360,000,000		$ 1,629,000,000
Total accruing loans contractually past due 90 days or more	46,000,000		80,000,000
Total nonperforming loans	1,406,000,000		1,709,000,000
Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	210,000,000		463,000,000
Total accruing loans contractually past due 90 days or more	9,000,000		37,000,000
Commercial Loan [Member] | Construction and land loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	44,000,000		104,000,000
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	103,000,000		281,000,000
Total accruing loans contractually past due 90 days or more	0		8,000,000
Commercial Loan [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	47,000,000		47,000,000
Total accruing loans contractually past due 90 days or more	0		28,000,000
Commercial Loan [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	14,000,000		18,000,000
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	2,000,000		13,000,000
Total accruing loans contractually past due 90 days or more	9,000,000		1,000,000
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	1,105,000,000		1,129,000,000
Total accruing loans contractually past due 90 days or more	37,000,000		43,000,000
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	1,020,000,000		1,038,000,000
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	85,000,000		86,000,000
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	1,105,000,000	[1]	1,124,000,000	[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	13,000,000		15,000,000
Consumer Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	0		5,000,000
Total accruing loans contractually past due 90 days or more	24,000,000		28,000,000
Nonaccrual Loans Held For Sale [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	$ 45,000,000		$ 37,000,000

[1] Nonaccrual residential mortgages includes all receivables which are 90 or more days contractually delinquent as well as loans discharged under Chapter 7 bankruptcy and not re-affirmed and second lien loans where the first lien loan that we own or service is 90 or more days contractually delinquent.