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, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013		Dec. 31, 2013	Sep. 30, 2012
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 574		$ 568		$ 606		$ 647			$ 605
Provision (credit) for credit losses	85		67		101	[1]	88	[1]
Charge-offs	(48)		(48)		(115)		(158)
Recoveries	13		18		32		28
Net (charge offs) recoveries	(35)		(30)		(83)		(130)
Balance at end of period	624		605		624		605			605
Ending balance: collectively evaluated for impairment	550		486		550		486
Ending balance: individually evaluated for impairment	74		119		74		119
Total allowances for credit losses	624		605		624		605			605
Collectively evaluated for impairment	70,098		64,278		70,098		64,278
Individually evaluated for impairment	508	[2]	859	[2]	508	[2]	859	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	1,592		1,568		1,592		1,568
Total loans	72,198		66,705		72,198		66,705		67,695
Commercial Loan [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans	53,033				53,033				48,494
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	93		116		108		162			110
Provision (credit) for credit losses	6		(14)		8		(5)
Charge-offs	(5)		(1)		(24)		(59)
Recoveries	0		9		2		12
Net (charge offs) recoveries	(5)		8		(22)		(47)
Balance at end of period	94		110		94		110			110
Ending balance: collectively evaluated for impairment	90		84		90		84
Ending balance: individually evaluated for impairment	4		26		4		26
Total allowances for credit losses	94		110		94		110			110
Collectively evaluated for impairment	9,469		8,064		9,469		8,064
Individually evaluated for impairment	213	[2]	465	[2]	213	[2]	465	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	9,682		8,529		9,682		8,529		9,034
Commercial Loan [Member] | Business and Corporate Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	129		96		112		97			103
Provision (credit) for credit losses	56		15		75		17
Charge-offs	(6)		(9)		(11)		(15)
Recoveries	1		1		4		4
Net (charge offs) recoveries	(5)		(8)		(7)		(11)
Balance at end of period	180		103		180		103			103
Ending balance: collectively evaluated for impairment	172		91		172		91
Ending balance: individually evaluated for impairment	8		12		8		12
Total allowances for credit losses	180		103		180		103			103
Collectively evaluated for impairment	15,913		12,323		15,913		12,323
Individually evaluated for impairment	43	[2]	68	[2]	43	[2]	68	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	15,956		12,391		15,956		12,391		14,446
Commercial Loan [Member] | Global Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	67		40		68		41			69
Provision (credit) for credit losses	29		29		36		28
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		69		96		69			69
Ending balance: collectively evaluated for impairment	96		69		96		69
Ending balance: individually evaluated for impairment	0		0		0		0
Total allowances for credit losses	96		69		96		69			69
Collectively evaluated for impairment	24,268		23,321		24,268		23,321
Individually evaluated for impairment	0	[2]	18	[2]	0	[2]	18	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	24,268		23,339		24,268		23,339		21,625
Commercial Loan [Member] | Other Commercial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	19		17		20		17			17
Provision (credit) for credit losses	(9)		(4)		(13)		(4)
Charge-offs	0		0		0		0
Recoveries	3		4		6		4
Net (charge offs) recoveries	3		4		6		4
Balance at end of period	13		17		13		17			17
Ending balance: collectively evaluated for impairment	11		17		11		17
Ending balance: individually evaluated for impairment	2		0		2		0
Total allowances for credit losses	13		17		13		17			17
Collectively evaluated for impairment	3,117		2,941		3,117		2,941
Individually evaluated for impairment	10	[2]	64	[2]	10	[2]	64	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	3,127		3,005		3,127		3,005		3,389
Consumer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans	19,165				19,165				19,201
Consumer Loans [Member] | Residential Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	156		192		186		210			196
Provision (credit) for credit losses	7		14		(9)		11
Charge-offs	(19)		(13)		(36)		(29)
Recoveries	5		3		8		4
Net (charge offs) recoveries	(14)		(10)		(28)		(25)
Balance at end of period	149		196		149		196			196
Ending balance: collectively evaluated for impairment	93		122		93		122
Ending balance: individually evaluated for impairment	56		74		56		74
Total allowances for credit losses	149		196		149		196			196
Collectively evaluated for impairment	14,290		14,057		14,290		14,057
Individually evaluated for impairment	215	[2]	212	[2]	215	[2]	212	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	1,592		1,568		1,592		1,568
Total loans	16,097		15,837		16,097		15,837		15,826
Consumer Loans [Member] | Home Equity Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	52		50		49		45			52
Provision (credit) for credit losses	(8)		13		(6)		30
Charge-offs	(3)		(11)		(8)		(23)
Recoveries	1		0		7		0
Net (charge offs) recoveries	(2)		(11)		(1)		(23)
Balance at end of period	42		52		42		52			52
Ending balance: collectively evaluated for impairment	40		49		40		49
Ending balance: individually evaluated for impairment	2		3		2		3
Total allowances for credit losses	42		52		42		52			52
Collectively evaluated for impairment	1,895		2,151		1,895		2,151
Individually evaluated for impairment	19	[2]	21	[2]	19	[2]	21	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	1,914		2,172		1,914		2,172		2,011
Consumer Loans [Member] | Credit Card [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	45		42		50		55			45
Provision (credit) for credit losses	4		13		9		11
Charge-offs	(12)		(11)		(23)		(23)
Recoveries	2		1		3		2
Net (charge offs) recoveries	(10)		(10)		(20)		(21)
Balance at end of period	39		45		39		45			45
Ending balance: collectively evaluated for impairment	37		41		37		41
Ending balance: individually evaluated for impairment	2		4		2		4
Total allowances for credit losses	39		45		39		45			45
Collectively evaluated for impairment	673		847		673		847
Individually evaluated for impairment	8	[2]	11	[2]	8	[2]	11	[2]
Loans carried at the lower of amortized cost or fair value less cost to sell	0		0		0		0
Total loans	681		858		681		858		854
Consumer Loans [Member] | Other consumer [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	13		15		13		20			13
Provision (credit) for credit losses	0		1		1		0
Charge-offs	(3)		(3)		(5)		(9)
Recoveries	1		0		2		2
Net (charge offs) recoveries	(2)		(3)		(3)		(7)
Balance at end of period	11		13		11		13			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			13
Collectively evaluated for impairment	473		574		473		574
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	$ 473		$ 574		$ 473		$ 574		$ 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 $725 million and $657 million at June 30, 2014 and 2013, respectively.