Loans - Summary of TDR and Related Credit Loss Reserves for TDR Loans (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012
Financing Receivable, Impaired [Line Items]
TDR Loans	$ 1,435	[1],[2],[3]	$ 1,434	[1],[2],[3]
Individually evaluated for impairment	846	[4]			1,253	[4]
Allowance for credit losses on TDR Loans	117	[5]	140	[5]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	129				246
Unpaid Principal Balance of TDR Loans	1,674		1,701
Commercial Loan [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	504	[1],[2]	460	[1],[2]
Allowance for credit losses on TDR Loans	46	[5]	26	[5]
Unpaid Principal Balance of TDR Loans	563		569
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	375	[1],[2]	343	[1],[2]
Individually evaluated for impairment	420	[4]			533	[4]
Allowance for credit losses on TDR Loans	12	[5]	23	[5]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	17				102
Unpaid Principal Balance of TDR Loans	393		398
Commercial Loan [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	51	[1],[2]	86	[1],[2]
Individually evaluated for impairment	56	[4]			108	[4]
Allowance for credit losses on TDR Loans	30	[5]	3	[5]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	32				10
Unpaid Principal Balance of TDR Loans	89		137
Commercial Loan [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	51	[1],[2]	0	[1],[2]
Individually evaluated for impairment	65	[4]			143	[4]
Allowance for credit losses on TDR Loans	4	[5]	0	[5]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	9				15
Unpaid Principal Balance of TDR Loans	51		0
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	27	[1],[2]	31	[1],[2]
Individually evaluated for impairment	61	[4]			86	[4]
Allowance for credit losses on TDR Loans	0	[5]	0	[5]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0				1
Unpaid Principal Balance of TDR Loans	30		34
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	931	[1],[2]	974	[1],[2]
Allowance for credit losses on TDR Loans	71	[5]	114	[5]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0
Unpaid Principal Balance of TDR Loans	1,111		1,132
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	921	[1],[2],[6]	960	[1],[2],[6]
Individually evaluated for impairment	215	[4]			345	[4]
Allowance for credit losses on TDR Loans	68	[5]	109	[5]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	66				107
Unpaid Principal Balance of TDR Loans	1,101		1,118
Consumer Loans [Member] | Credit Card Receivables [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans			14	[1],[2]
Individually evaluated for impairment	10	[1],[2]			16	[4]
Allowance for credit losses on TDR Loans			5	[5]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	3	[5]			5
Unpaid Principal Balance of TDR Loans	$ 10		$ 14

[1] TDR Loans are considered to be impaired loans. For consumer loans, all such loans are considered impaired loans regardless of accrual status. For commercial loans, impaired loans include other loans in addition to TDRs which totaled $98 million and $237 million at September 30, 2013 and December 31, 2012, respectively.

[2] The TDR Loan balances included in the table above reflect the current carrying amount of TDR Loans and includes all basis adjustments on the loan, such as unearned income, unamortized deferred fees and costs on originated loans, partial charge-offs and premiums or discounts on purchased loans. The following table reflects the unpaid principal balance of TDR Loans: September 30, 2013 December 31, 2012 (in millions)Commercial loans: Construction and other real estate$393 $398Business and corporate banking89 137Global banking51 —Other commercial30 34Total commercial563 569Consumer loans: Residential mortgages1,101 1,118Credit cards10 14Total consumer1,111 1,132Total$1,674 $1,701

[3] Includes $404 million and $519 million at September 30, 2013 and December 31, 2012, respectively, which are classified as nonaccrual loans.

[4] For consumer loans, these amounts represent TDR Loans for which we evaluate reserves using a discounted cash flow methodology. Each loan is individually identified as a TDR Loan and then grouped together with other TDR Loans with similar characteristics. The discounted cash flow analysis is then applied to these groups of TDR Loans. Loans individually evaluated for impairment exclude TDR loans that are carried at the lower of amortized cost or fair value of the collateral less cost to sell which totaled $687 million and $516 million at September 30, 2013 and 2012, respectively.

[5] Included in the allowance for credit losses.

[6] Includes $687 million and $608 million at September 30, 2013 and December 31, 2012, respectively, of loans that are recorded at the lower of amortized cost or fair value of the collateral less cost to sell.