Loans - Summary of TDR and Related Credit Loss Reserves for TDR Loans (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
TDR Loans	$ 1,206	[1],[2],[3]	$ 1,370	[1],[2],[3]
Allowance for credit losses on TDR Loans	64	[4]	87	[4]
Unpaid Principal Balance of TDR Loans	1,442		1,609
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	229	[1],[2]	389	[1],[2]
Allowance for credit losses on TDR Loans	9	[4]	17	[4]
Unpaid Principal Balance of TDR Loans	275		448
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	200	[1],[2]	292	[1],[2]
Allowance for credit losses on TDR Loans	2	[4]	16	[4]
Unpaid Principal Balance of TDR Loans	215		309
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	29	[1],[2]	21	[1],[2]
Allowance for credit losses on TDR Loans	7	[4]	1	[4]
Unpaid Principal Balance of TDR Loans	60		60
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	0	[1],[2]	51	[1],[2]
Unpaid Principal Balance of TDR Loans	0		51
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	0	[1],[2]	25	[1],[2]
Unpaid Principal Balance of TDR Loans	0		28
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	977	[1],[2]	981	[1],[2]
Allowance for credit losses on TDR Loans	55	[4]	70	[4]
Unpaid Principal Balance of TDR Loans	1,167		1,161
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	950	[1],[2],[5]	953	[1],[2],[5]
Allowance for credit losses on TDR Loans	51		66	[4]
Unpaid Principal Balance of TDR Loans	1,116		1,113
Consumer Loans [Member] | Home Equity Line of Credit [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	20	[1],[2],[5]	20	[1],[2],[5]
Allowance for credit losses on TDR Loans	2	[4]	2	[4]
Unpaid Principal Balance of TDR Loans	44		40
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Impaired [Line Items]
TDR Loans	7	[1],[2]	8	[1],[2]
Allowance for credit losses on TDR Loans	2	[4]	2	[4]
Unpaid Principal Balance of TDR Loans	$ 7		$ 8

[1] 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, 2014 December 31, 2013 (in millions)Commercial loans: Construction and other real estate$215 $309Business and corporate banking60 60Global banking— 51Other commercial— 28Total commercial275 448Consumer loans: Residential mortgages1,116 1,113 Home equity mortgages44 40Credit cards7 8Total consumer1,167 1,161Total$1,442 $1,609

[2] 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 TDR Loans which totaled $20 million and $92 million at September 30, 2014 and December 31, 2013, respectively.

[3] Includes $478 million and $528 million at September 30, 2014 and December 31, 2013, respectively, of loans which are classified as nonaccrual.

[4] Included in the allowance for credit losses.

[5] Includes $741 million and $706 million at September 30, 2014 and December 31, 2013, respectively, of loans, primarily residential mortgages, that are recorded at the lower of amortized cost or fair value of the collateral less cost to sell.