Loans - Summary of Nonaccrual Loans and Accruing Receivables 90 Days or More Delinquent (Detail) - USD ($) $ in Millions		Sep. 30, 2016		Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans		$ 1,726		$ 1,179
Total accruing loans contractually past due 90 days or more		17		17
Total nonperforming loans		1,743		1,196
Residential Mortgage Loan Nonaccrual Carried At Lower Of Amortized Cost Or Fair Value Less Cost To Sell		318		768
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest		848		265
Total nonaccruing loans		848		291
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]
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest		24		53
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]
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest		202		167
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]
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest		621		44
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]
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest		1		1
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		0		26
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest		462		885
Total nonaccruing loans		878		888
Total accruing loans contractually past due 90 days or more		16		16
Consumer Loans [Member] | Nonaccrual Loans Held-for-sale [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans	[1]	416		3
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest	[1],[2],[3],[4]	389		814
Total accruing loans contractually past due 90 days or more		0	[5]	0
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest	[2],[4]	73		71
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]
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest		0		0
Total accruing loans contractually past due 90 days or more		9		9
Consumer Loans [Member] | Other consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest		0		0
Total accruing loans contractually past due 90 days or more		$ 7		$ 7

[1] The trend in nonaccrual loans reflects the impact of transfers of certain residential mortgage loans to held for sale during the nine months ended September 30, 2016.

[2] At September 30, 2016 and December 31, 2015, nonaccrual consumer mortgage loans held for investment include $318 million and $768 million, respectively, of loans that are carried at the lower of amortized cost or fair value of the collateral less cost to sell.

[3] Nonaccrual consumer mortgage loans for all periods does not include guaranteed loans purchased from the Government National Mortgage Association. 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.

[4] Nonaccrual consumer mortgage loans held for investment include all loans 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.

[5] The decrease in nonaccrual loans at September 30, 2016 reflects the impact of transfers of certain residential mortgage loans to held for sale during the nine months ended September 30, 2016.