Loans - Summary of Nonaccrual Loans and Accruing Receivables 90 Days or More Delinquent (Detail) - USD ($) $ in Millions		Mar. 31, 2016		Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonaccruing loans		$ 1,398		$ 1,179
Total accruing loans contractually past due 90 days or more		17		17
Total nonperforming loans		1,415		1,196
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest		503		265
Total nonaccruing loans		503		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		53		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		199		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		250		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		518		885
Total nonaccruing loans		895		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]	377		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]	447		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]	71		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 the transfer of certain residential mortgage loans with a carrying value of $345 million to held for sale during the first quarter of 2016.

[2] At March 31, 2016 and December 31, 2015, nonaccrual consumer mortgage loans held for investment include $451 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 March 31, 2016 reflects the impact of the transfer of certain residential mortgage loans with a carrying value of $345 million to held for sale during the first quarter of 2016.