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, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 624		$ 605		$ 606		$ 647
Provision for credit losses	23	[1]	54	[1]	124	[1]	142	[1]
Charge offs	(29)		(73)		(144)		(231)
Recoveries	13		9		45		37
Net (charge offs) recoveries	(16)		(64)		(99)		(194)
Balance at end of period	631		595		631		595
Ending balance: collectively evaluated for impairment	566		466		566		466
Ending balance: individually evaluated for impairment	65		129		65		129
Total allowances for credit losses	631		595		631		595
Collectively evaluated for impairment	71,372		65,258		71,372		65,258
Individually evaluated for impairment	485	[2]	846	[2]	485	[2]	846	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	1,582		1,606		1,582		1,606
Total loans	73,439		67,710		73,439		67,710		67,695
Commercial Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans	54,062				54,062				48,494
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	94		110		108		162
Provision for credit losses	(9)		(10)		(1)		(15)
Charge offs	0		(3)		(24)		(62)
Recoveries	1		1		3		13
Net (charge offs) recoveries	1		(2)		(21)		(49)
Balance at end of period	86		98		86		98
Ending balance: collectively evaluated for impairment	84		81		84		81
Ending balance: individually evaluated for impairment	2		17		2		17
Total allowances for credit losses	86		98		86		98
Collectively evaluated for impairment	9,459		8,499		9,459		8,499
Individually evaluated for impairment	202	[2]	420	[2]	202	[2]	420	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	9,661		8,919		9,661		8,919		9,034
Commercial Loans [Member] | Business and Corporate Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	180		103		112		97
Provision for credit losses	36		28		111		45
Charge offs	(5)		(3)		(16)		(18)
Recoveries	2		3		6		7
Net (charge offs) recoveries	(3)		0		(10)		(11)
Balance at end of period	213		131		213		131
Ending balance: collectively evaluated for impairment	206		99		206		99
Ending balance: individually evaluated for impairment	7		32		7		32
Total allowances for credit losses	213		131		213		131
Collectively evaluated for impairment	17,318		13,612		17,318		13,612
Individually evaluated for impairment	37	[2]	56	[2]	37	[2]	56	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	17,355		13,668		17,355		13,668		14,446
Commercial Loans [Member] | Global Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	96		69		68		41
Provision for credit losses	0		(2)		36		26
Charge offs	0		0		(8)		0
Recoveries	0		0		0		0
Net (charge offs) recoveries	0		0		(8)		0
Balance at end of period	96		67		96		67
Ending balance: collectively evaluated for impairment	96		58		96		58
Ending balance: individually evaluated for impairment	0		9		0		9
Total allowances for credit losses	96		67		96		67
Collectively evaluated for impairment	24,001		23,305		24,001		23,305
Individually evaluated for impairment	0	[2]	65	[2]	0	[2]	65	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	24,001		23,370		24,001		23,370		21,625
Commercial Loans [Member] | Other Commercial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	13		17		20		17
Provision for credit losses	1		0		(12)		(4)
Charge offs	0		0		0		0
Recoveries	3		0		9		4
Net (charge offs) recoveries	3		0		9		4
Balance at end of period	17		17		17		17
Ending balance: collectively evaluated for impairment	16		17		16		17
Ending balance: individually evaluated for impairment	1		0		1		0
Total allowances for credit losses	17		17		17		17
Collectively evaluated for impairment	3,035		2,491		3,035		2,491
Individually evaluated for impairment	10	[2]	61	[2]	10	[2]	61	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	3,045		2,552		3,045		2,552		3,389
Consumer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans	19,377				19,377				19,201
Consumer Loans [Member] | Residential Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	149		196		186		210
Provision for credit losses	(11)		(1)		(20)		10
Charge offs	(9)		(40)		(45)		(69)
Recoveries	3		3		11		7
Net (charge offs) recoveries	(6)		(37)		(34)		(62)
Balance at end of period	132		158		132		158
Ending balance: collectively evaluated for impairment	81		92		81		92
Ending balance: individually evaluated for impairment	51		66		51		66
Total allowances for credit losses	132		158		132		158
Collectively evaluated for impairment	14,662		13,963		14,662		13,963
Individually evaluated for impairment	224	[2]	215	[2]	224	[2]	215	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	1,516		1,542		1,516		1,542
Total loans	16,402		15,720		16,402		15,720		15,826
Consumer Loans [Member] | Home Equity Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	42		52		49		45
Provision for credit losses	(5)		28		(11)		58
Charge offs	(3)		(15)		(11)		(38)
Recoveries	2		1		9		1
Net (charge offs) recoveries	(1)		(14)		(2)		(37)
Balance at end of period	36		66		36		66
Ending balance: collectively evaluated for impairment	34		64		34		64
Ending balance: individually evaluated for impairment	2		2		2		2
Total allowances for credit losses	36		66		36		66
Collectively evaluated for impairment	1,753		2,004		1,753		2,004
Individually evaluated for impairment	5	[2]	19	[2]	5	[2]	19	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	66		64		66		64
Total loans	1,824		2,087		1,824		2,087		2,011
Consumer Loans [Member] | Credit Card [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	39		45		50		55
Provision for credit losses	9		10		18		21
Charge offs	(10)		(11)		(33)		(34)
Recoveries	2		1		5		3
Net (charge offs) recoveries	(8)		(10)		(28)		(31)
Balance at end of period	40		45		40		45
Ending balance: collectively evaluated for impairment	38		42		38		42
Ending balance: individually evaluated for impairment	2		3		2		3
Total allowances for credit losses	40		45		40		45
Collectively evaluated for impairment	679		846		679		846
Individually evaluated for impairment	7	[2]	10	[2]	7	[2]	10	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	686		856		686		856		854
Consumer Loans [Member] | Other consumer [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	11		13		13		20
Provision for credit losses	2		1		3		1
Charge offs	(2)		(1)		(7)		(10)
Recoveries	0		0		2		2
Net (charge offs) recoveries	(2)		(1)		(5)		(8)
Balance at end of period	11		13		11		13
Ending balance: collectively evaluated for impairment	11		13		11		13
Ending balance: individually evaluated for impairment	0		0		0		0
Total allowances for credit losses	11		13		11		13
Collectively evaluated for impairment	465		538		465		538
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	$ 465		$ 538		$ 465		$ 538		$ 510

[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 and certain small business 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 $741 million and $687 million at September 30, 2014 and 2013, respectively.