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				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 568		$ 603		$ 647		$ 743
Provision for credit losses	67	[1]	89	[1]	88	[1]	89	[1]
Charge-offs	(48)		(91)		(158)		(253)
Recoveries	18		18		28		40
Net (charge offs) recoveries	(30)		(73)		(130)		(213)
Balance at end of period	605		619		605		619
Ending balance: collectively evaluated for impairment	486		384		486		384
Ending balance: individually evaluated for impairment	119		235		119		235
Total allowances for credit losses	605		619		605		619
Collectively evaluated for impairment	64,278		53,610		64,278		53,610
Individually evaluated for impairment	859	[2]	1,599	[2]	859	[2]	1,599	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	1,568		855		1,568		855
Total loans	66,705		56,064		66,705		56,064		63,258
Commercial Loan [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans	47,264				47,264				44,150
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	116		205		162		212
Provision for credit losses	(14)		(5)		(5)		(25)
Charge-offs	(1)		(2)		(59)		(3)
Recoveries	9		0		12		14
Net (charge offs) recoveries	8		(2)		(47)		11
Balance at end of period	110		198		110		198
Ending balance: collectively evaluated for impairment	84		87		84		87
Ending balance: individually evaluated for impairment	26		111		26		111
Total allowances for credit losses	110		198		110		198
Collectively evaluated for impairment	8,064		7,386		8,064		7,386
Individually evaluated for impairment	465		591		465		591
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	8,529		7,977		8,529		7,977		8,457
Commercial Loan [Member] | Business and Corporate Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	96		76		97		78
Provision for credit losses	15		15		17		21
Charge-offs	(9)		(13)		(15)		(23)
Recoveries	1		2		4		4
Net (charge offs) recoveries	(8)		(11)		(11)		(19)
Balance at end of period	103		80		103		80
Ending balance: collectively evaluated for impairment	91		73		91		73
Ending balance: individually evaluated for impairment	12		7		12		7
Total allowances for credit losses	103		80		103		80
Collectively evaluated for impairment	12,323		11,141		12,323		11,141
Individually evaluated for impairment	68		115		68		115
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	12,391		11,256		12,391		11,256		12,608
Commercial Loan [Member] | Global Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	40		25		41		131
Provision for credit losses	29		19		28		(3)
Charge-offs	0		0		0		(84)
Recoveries	0		0		0		0
Net (charge offs) recoveries	0		0		0		(84)
Balance at end of period	69		44		69		44
Ending balance: collectively evaluated for impairment	69		31		69		31
Ending balance: individually evaluated for impairment	0		13		0		13
Total allowances for credit losses	69		44		69		44
Collectively evaluated for impairment	23,321		14,928		23,321		14,928
Individually evaluated for impairment	18		114		18		114
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	23,339		15,042		23,339		15,042		20,009
Commercial Loan [Member] | Other Commercial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	17		20		17		21
Provision for credit losses	(4)		(7)		(4)		(9)
Charge-offs	0		0		0		0
Recoveries	4		5		4		6
Net (charge offs) recoveries	4		5		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	2,941		3,055		2,941		3,055
Individually evaluated for impairment	64		87		64		87
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	3,005		3,142		3,005		3,142		3,076
Consumer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period									114
Balance at end of period	95				95				114
Ending balance: individually evaluated for impairment	0				0
Total allowances for credit losses	95				95				114
Total loans	19,441				19,441				19,108
Consumer Loans [Member] | Residential Mortgage [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	192		182		210		192
Provision for credit losses	14		24		11		39
Charge-offs	(13)		(23)		(29)		(49)
Recoveries	3		5		4		6
Net (charge offs) recoveries	(10)		(18)		(25)		(43)
Balance at end of period	196		188		196		188
Ending balance: collectively evaluated for impairment	122		95		122		95
Ending balance: individually evaluated for impairment	74		93		74		93
Total allowances for credit losses	196		188		196		188
Collectively evaluated for impairment	14,057		13,243		14,057		13,243
Individually evaluated for impairment	212	[2]	660	[2]	212	[2]	660	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	1,568		855		1,568		855
Total loans	15,837		14,758		15,837		14,758		15,371
Consumer Loans [Member] | Home Equity Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	50		43		45		52
Provision for credit losses	13		34		30		42
Charge-offs	(11)		(30)		(23)		(47)
Recoveries	0		0		0		0
Net (charge offs) recoveries	(11)		(30)		(23)		(47)
Balance at end of period	52		47		52		47
Ending balance: collectively evaluated for impairment	49		43		49		43
Ending balance: individually evaluated for impairment	3		4		3		4
Total allowances for credit losses	52		47		52		47
Collectively evaluated for impairment	2,151		2,441		2,151		2,441
Individually evaluated for impairment	21	[2]	14	[2]	21	[2]	14	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	2,172		2,455		2,172		2,455		2,324
Consumer Loans [Member] | Credit Card [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	42		35		55		39
Provision for credit losses	13		9		11		20
Charge-offs	(11)		(16)		(23)		(33)
Recoveries	1		3		2		5
Net (charge offs) recoveries	(10)		(13)		(21)		(28)
Balance at end of period	45		31		45		31
Ending balance: collectively evaluated for impairment	41		25		41		25
Ending balance: individually evaluated for impairment	4		6		4		6
Total allowances for credit losses	45		31		45		31
Collectively evaluated for impairment	847		765		847		765
Individually evaluated for impairment	11		18	[2]	11		18	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	858		783		858		783		815
Consumer Loans [Member] | Other Consumer [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	15		17		20		18
Provision for credit losses	1		0		0		4
Charge-offs	(3)		(7)		(9)		(14)
Recoveries	0		3		2		5
Net (charge offs) recoveries	(3)		(4)		(7)		(9)
Balance at end of period	13		13		13		13
Ending balance: collectively evaluated for impairment	13		13		13		13
Ending balance: individually evaluated for impairment			0				0
Total allowances for credit losses	13		13		13		13
Collectively evaluated for impairment	574		651		574		651
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	$ 574		$ 651		$ 574		$ 651		$ 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] (1) 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 $657 million and $510 million at June 30, 2013 and 2012, respectively.