Loans - Summary of Nonaccrual Loans and Accruing Receivables 90 Days or More Delinquent (Detail) - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans		$ 1,062	$ 1,101
Total accruing loans contractually past due 90 days or more		20	21
Total nonperforming loans		1,082	1,122
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans		144	139
Total nonaccruing loans		202	182
Total accruing loans contractually past due 90 days or more		1	1
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans		49	65
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	74
Total accruing loans contractually past due 90 days or more		1	1
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans		21	0
Total accruing loans contractually past due 90 days or more		0	0
Commercial Loans [Member] | Nonaccrual Loans Held-for-sale [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans		58	43
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans		857	915
Total nonaccruing loans		860	919
Total accruing loans contractually past due 90 days or more		19	20
Consumer Loans [Member] | Nonaccrual Loans Held-for-sale [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans		3	4
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans	[1],[2],[3]	790	847
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	[1],[3]	67	68
Total accruing loans contractually past due 90 days or more		0	0
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans		0	0
Total accruing loans contractually past due 90 days or more		9	10
Consumer Loans [Member] | Other consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual Loans	[1],[3]	0	0
Total accruing loans contractually past due 90 days or more		$ 10	$ 10

[1] At September 30, 2015 and December 31, 2014, nonaccrual consumer mortgage loans include $740 million and $817 million, respectively, of loans that are carried at the lower of amortized cost or fair value of the collateral less cost to sell.

[2] Nonaccrual consumer mortgage 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 consumer loan portfolio.

[3] Nonaccrual consumer mortgage loans include 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.