Loans - Summary of Nonaccrual Loans and Accruing Receivables 90 Days or More Delinquent (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	$ 1,101		$ 1,305
Total accruing loans contractually past due 90 days or more	21		34
Total nonperforming loans	1,122		1,339
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	182		254
Nonaccrual loans	139		254
Total accruing loans contractually past due 90 days or more	1		6
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	65		166
Total accruing loans contractually past due 90 days or more	0		0
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	74		21
Total accruing loans contractually past due 90 days or more	1		5
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	0		65
Total accruing loans contractually past due 90 days or more	0		0
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	0		2
Total accruing loans contractually past due 90 days or more	0		1
Commercial Loans [Member] | Nonaccrual Loans Held-for-sale [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	43		0
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	919		1,051
Nonaccrual loans	915		1,026
Total accruing loans contractually past due 90 days or more	20		28
Consumer Loans [Member] | Nonaccrual Loans Held-for-sale [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	4		25
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	847		949
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]
Nonaccrual loans	68		77
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]
Nonaccrual loans	915	[1],[2],[3]	1,026	[1],[2],[3]
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	10		14
Consumer Loans [Member] | Other consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual loans	0		0
Total accruing loans contractually past due 90 days or more	$ 10		$ 14

[1] At December 31, 2014 and 2013, residential mortgage loan nonaccrual balances include $817 million and $841 million, respectively, of loans that are carried at the lower of amortized cost or fair value of the collateral less cost to sell.

[2] Residential mortgage nonaccrual loans for all periods does not include guaranteed loans purchased from the Government National Mortgage Association ("GNMA"). Repayment of these loans are predominantly insured by the Federal Housing Administration and as such, these loans have different risk characteristics from the rest of our customer loan portfolio.

[3] 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.