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										12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period					$ 606					$ 647	$ 606		$ 647		$ 743
Provision for credit losses	64		23	85	16	51		54	67	21	188		193		293
Charge offs											(169)		(288)		(452)
Recoveries											55		54		63
Net (charge offs) recoveries											(114)		(234)		(389)
Balance at end of period	680					606					680		606		647
Ending balance: collectively evaluated for impairment	603					496					603		496		437
Ending balance: individually evaluated for impairment	77					110					77		110		210
Total allowances for credit losses	680					606					680		606		647
Collectively evaluated for impairment	75,630					65,341					75,630		65,341		60,718
Individually evaluated for impairment	530	[1]				742	[1]				530	[1]	742	[1]	1,063	[1]
Loans carried at the lower of amortized cost or fair value less cost to sell	1,581					1,612					1,581		1,612		1,477
Total loans	77,741					67,695					77,741		67,695		63,258
Commercial Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans	58,087					48,494					58,087		48,494
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period					108					162	108		162		212
Provision for credit losses											2		(7)		(33)
Charge offs											(24)		(62)		(36)
Recoveries											3		15		19
Net (charge offs) recoveries											(21)		(47)		(17)
Balance at end of period	89					108					89		108		162
Ending balance: collectively evaluated for impairment	84					76					84		76		76
Ending balance: individually evaluated for impairment	5					32					5		32		86
Total allowances for credit losses	89					108					89		108		162
Collectively evaluated for impairment	10,103					8,701					10,103		8,701		7,960
Individually evaluated for impairment	197	[1]				333	[1]				197	[1]	333	[1]	497	[1]
Loans carried at the lower of amortized cost or fair value less cost to sell	0					0					0		0		0
Total loans	10,300					9,034					10,300		9,034		8,457
Commercial Loans [Member] | Business and Corporate Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period					112					97	112		97		78
Provision for credit losses											174		48		48
Charge offs											(19)		(42)		(37)
Recoveries											8		9		8
Net (charge offs) recoveries											(11)		(33)		(29)
Balance at end of period	275					112					275		112		97
Ending balance: collectively evaluated for impairment	251					109					251		109		87
Ending balance: individually evaluated for impairment	24					3					24		3		10
Total allowances for credit losses	275					112					275		112		97
Collectively evaluated for impairment	17,729					14,420					17,729		14,420		12,502
Individually evaluated for impairment	90	[1]				26	[1]				90	[1]	26	[1]	106	[1]
Loans carried at the lower of amortized cost or fair value less cost to sell	0					0					0		0		0
Total loans	17,819					14,446					17,819		14,446		12,608
Commercial Loans [Member] | Global Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period					68					41	68		41		131
Provision for credit losses											47		26		14
Charge offs											(8)		0		(105)
Recoveries											0		1		1
Net (charge offs) recoveries											(8)		1		(104)
Balance at end of period	107					68					107		68		41
Ending balance: collectively evaluated for impairment	107					63					107		63		41
Ending balance: individually evaluated for impairment	0					5					0		5		0
Total allowances for credit losses	107					68					107		68		41
Collectively evaluated for impairment	26,387					21,560					26,387		21,560		19,991
Individually evaluated for impairment	0	[1]				65	[1]				0	[1]	65	[1]	18	[1]
Loans carried at the lower of amortized cost or fair value less cost to sell	0					0					0		0		0
Total loans	26,387					21,625					26,387		21,625		20,009
Commercial Loans [Member] | Other Commercial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period					20					17	20		17		21
Provision for credit losses											(7)		(5)		(10)
Charge offs											(1)		0		(1)
Recoveries											9		8		7
Net (charge offs) recoveries											8		8		6
Balance at end of period	21					20					21		20		17
Ending balance: collectively evaluated for impairment	20					20					20		20		17
Ending balance: individually evaluated for impairment	1					0					1		0		0
Total allowances for credit losses	21					20					21		20		17
Collectively evaluated for impairment	3,573					3,346					3,573		3,346		3,000
Individually evaluated for impairment	8	[1]				43	[1]				8	[1]	43	[1]	76	[1]
Loans carried at the lower of amortized cost or fair value less cost to sell	0					0					0		0		0
Total loans	3,581					3,389					3,581		3,389		3,076
Consumer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans	19,654					19,201					19,654		19,201
Consumer Loans [Member] | Residential Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period					186					210	186		210		192
Provision for credit losses											(40)		42		114
Charge offs											(55)		(78)		(107)
Recoveries											16		12		11
Net (charge offs) recoveries											(39)		(66)		(96)
Balance at end of period	107					186					107		186		210
Ending balance: collectively evaluated for impairment	64					120					64		120		105
Ending balance: individually evaluated for impairment	43					66					43		66		105
Total allowances for credit losses	107					186					107		186		210
Collectively evaluated for impairment	14,926					14,034					14,926		14,034		13,633
Individually evaluated for impairment	224	[1]				247	[1]				224	[1]	247	[1]	331	[1]
Loans carried at the lower of amortized cost or fair value less cost to sell	1,511					1,545					1,511		1,545		1,407
Total loans	16,661					15,826					16,661		15,826		15,371
Consumer Loans [Member] | Home Equity Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period					49					45	49		45		52
Provision for credit losses											(14)		54		72
Charge offs											(13)		(52)		(79)
Recoveries											10		2		0
Net (charge offs) recoveries											(3)		(50)		(79)
Balance at end of period	32					49					32		49		45
Ending balance: collectively evaluated for impairment	30					47					30		47		41
Ending balance: individually evaluated for impairment	2					2					2		2		4
Total allowances for credit losses	32					49					32		49		45
Collectively evaluated for impairment	1,709					1,924					1,709		1,924		2,233
Individually evaluated for impairment	5	[1]				20	[1]				5	[1]	20	[1]	21	[1]
Loans carried at the lower of amortized cost or fair value less cost to sell	70					67					70		67		70
Total loans	1,784	[2]				2,011					1,784	[2]	2,011		2,324
Consumer Loans [Member] | Credit Card [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period					50					55	50		55		39
Provision for credit losses											23		32		67
Charge offs											(41)		(41)		(62)
Recoveries											7		4		11
Net (charge offs) recoveries											(34)		(37)		(51)
Balance at end of period	39					50					39		50		55
Ending balance: collectively evaluated for impairment	37					48					37		48		50
Ending balance: individually evaluated for impairment	2					2					2		2		5
Total allowances for credit losses	39					50					39		50		55
Collectively evaluated for impairment	714					846					714		846		801
Individually evaluated for impairment	6	[1]				8	[1]				6	[1]	8	[1]	14	[1]
Loans carried at the lower of amortized cost or fair value less cost to sell	0					0					0		0		0
Total loans	720	[3]				854					720	[3]	854		815
Consumer Loans [Member] | Other consumer [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period					13					20	13		20		18
Provision for credit losses											3		3		21
Charge offs											(8)		(13)		(25)
Recoveries											2		3		6
Net (charge offs) recoveries											(6)		(10)		(19)
Balance at end of period	10					13					10		13		20
Ending balance: collectively evaluated for impairment	10					13					10		13		20
Ending balance: individually evaluated for impairment	0					0					0		0		0
Total allowances for credit losses	10					13					10		13		20
Collectively evaluated for impairment	489					510					489		510		598
Individually evaluated for impairment	0	[1]				0	[1]				0	[1]	0	[1]	0	[1]
Loans carried at the lower of amortized cost or fair value less cost to sell	0					0					0		0		0
Total loans	$ 489					$ 510					$ 489		$ 510		$ 598

[1] 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 $763 million, $706 million and $608 million at December 31, 2014, 2013 and 2012, respectively.

[2] Home equity mortgage maturities reflect estimates based on historical payment patterns.

[3] As credit card receivables do not have stated maturities, the table reflects estimates based on historical payment patterns.