Allowance for Credit Losses - Summary of Changes in Allowance for Credit Losses and Related Loan Balance by Product (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 605		$ 619		$ 647		$ 743
Provision for credit losses	54	[1]	84	[1]	142	[1]	173	[1]
Charge-offs	(73)		(76)		(231)		(329)
Recoveries	9		10		37		50
Net (charge offs) recoveries	(64)		(66)		(194)		(279)
Balance at end of period	595		637		595		637
Ending balance: collectively evaluated for impairment	466		391		466		391
Ending balance: individually evaluated for impairment	129		246		129		246
Total allowances for credit losses	595		637		595		637
Collectively evaluated for impairment	65,258		58,920		65,258		58,920
Individually evaluated for impairment	846	[2]	1,253	[2]	846	[2]	1,253	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	1,606		1,279		1,606		1,279
Total loans	67,710		61,452		67,710		61,452		63,258
Commercial Loan [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans	48,509				48,509				44,150
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	110		198		162		212
Provision for credit losses	(10)		(11)		(15)		(36)
Charge-offs	(3)		(9)		(62)		(12)
Recoveries	1		3		13		17
Net (charge offs) recoveries	(2)		(6)		(49)		5
Balance at end of period	98		181		98		181
Ending balance: collectively evaluated for impairment	81		79		81		79
Ending balance: individually evaluated for impairment	17		102		17		102
Total allowances for credit losses	98		181		98		181
Collectively evaluated for impairment	8,499		7,387		8,499		7,387
Individually evaluated for impairment	420	[2]	533	[2]	420	[2]	533	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	8,919		7,920		8,919		7,920		8,457
Commercial Loan [Member] | Business and Corporate Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	103		80		97		78
Provision for credit losses	32		18		49		39
Charge-offs	(7)		(8)		(22)		(31)
Recoveries	3		2		7		6
Net (charge offs) recoveries	(4)		(6)		(15)		(25)
Balance at end of period	131		92		131		92
Ending balance: collectively evaluated for impairment	99		82		99		82
Ending balance: individually evaluated for impairment	32		10		32		10
Total allowances for credit losses	131		92		131		92
Collectively evaluated for impairment	13,612		12,389		13,612		12,389
Individually evaluated for impairment	56	[2]	108	[2]	56	[2]	108	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	13,668		12,497		13,668		12,497		12,608
Commercial Loan [Member] | Global Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	69		44		41		131
Provision for credit losses	(2)		12		26		9
Charge-offs	0		0		0		(84)
Recoveries	0		0		0		0
Net (charge offs) recoveries	0		0		0		(84)
Balance at end of period	67		56		67		56
Ending balance: collectively evaluated for impairment	58		41		58		41
Ending balance: individually evaluated for impairment	9		15		9		15
Total allowances for credit losses	67		56		67		56
Collectively evaluated for impairment	23,305		18,868		23,305		18,868
Individually evaluated for impairment	65	[2]	143	[2]	65	[2]	143	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	23,370		19,011		23,370		19,011		20,009
Commercial Loan [Member] | Other Commercial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	17		18		17		21
Provision for credit losses	0		0		(4)		(9)
Charge-offs	0		0		0		0
Recoveries	0		0		4		6
Net (charge offs) recoveries	0		0		4		6
Balance at end of period	17		18		17		18
Ending balance: collectively evaluated for impairment	17		17		17		17
Ending balance: individually evaluated for impairment	0		1		0		1
Total allowances for credit losses	17		18		17		18
Collectively evaluated for impairment	2,491		3,054		2,491		3,054
Individually evaluated for impairment	61	[2]	86	[2]	61	[2]	86	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	2,552		3,140		2,552		3,140		3,076
Consumer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period									114
Balance at end of period	81				81				114
Ending balance: individually evaluated for impairment	0				0
Total allowances for credit losses	81				81				114
Total loans	19,201				19,201				19,108
Consumer Loans [Member] | Residential Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	196		188		210		192
Provision for credit losses	(1)		33		10		72
Charge-offs	(40)		(24)		(69)		(73)
Recoveries	3		3		7		9
Net (charge offs) recoveries	(37)		(21)		(62)		(64)
Balance at end of period	158		200		158		200
Ending balance: collectively evaluated for impairment	92		93		92		93
Ending balance: individually evaluated for impairment	66		107		66		107
Total allowances for credit losses	158		200		158		200
Collectively evaluated for impairment	13,899		13,462		13,899		13,462
Individually evaluated for impairment	215	[2]	345	[2]	215	[2]	345	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	1,606		1,279		1,606		1,279
Total loans	15,720		15,086		15,720		15,086		15,371
Consumer Loans [Member] | Home Equity Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	52		47		45		52
Provision for credit losses	28		13		58		55
Charge-offs	(15)		(18)		(38)		(65)
Recoveries	1		0		1		0
Net (charge offs) recoveries	(14)		(18)		(37)		(65)
Balance at end of period	66		42		66		42
Ending balance: collectively evaluated for impairment	64		36		64		36
Ending balance: individually evaluated for impairment	2		6		2		6
Total allowances for credit losses	66		42		66		42
Collectively evaluated for impairment	2,068		2,365		2,068		2,365
Individually evaluated for impairment	19	[2]	22	[2]	19	[2]	22	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	2,087		2,387		2,087		2,387		2,324
Consumer Loans [Member] | Credit Card [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	45		31		55		39
Provision for credit losses	6		15		17		35
Charge-offs	(7)		(14)		(30)		(47)
Recoveries	1		2		3		7
Net (charge offs) recoveries	(6)		(12)		(27)		(40)
Balance at end of period	45		34		45		34
Ending balance: collectively evaluated for impairment	42		29		42		29
Ending balance: individually evaluated for impairment	3	[3]	5		3	[3]	5
Total allowances for credit losses	45		34		45		34
Collectively evaluated for impairment	846		780		846		780
Individually evaluated for impairment	10	[4],[5]	16	[2]	10	[4],[5]	16	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	856		796		856		796		815
Consumer Loans [Member] | Other Consumer [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	13		13		20		18
Provision for credit losses	1		4		1		8
Charge-offs	(1)		(3)		(10)		(17)
Recoveries	0		0		2		5
Net (charge offs) recoveries	(1)		(3)		(8)		(12)
Balance at end of period	13		14		13		14
Ending balance: collectively evaluated for impairment	13		14		13		14
Ending balance: individually evaluated for impairment			0				0
Total allowances for credit losses	13		14		13		14
Collectively evaluated for impairment	538		615		538		615
Individually evaluated for impairment	0	[2]	0	[2]	0	[2]	0	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	$ 538		$ 615		$ 538		$ 615		$ 598

[1] The provision assigned to the segments is based on the segments’ net charge offs and the change in allowance for credit losses.

[2] 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.

[3] Included in the allowance for credit losses.

[4] 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.

[5] 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