Allowance for Credit Losses - Summary of Changes in Allowance for Credit Losses and Related Loan Balance by Product (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		$ 703	$ 574	$ 680	$ 606
Provision for credit losses		(6)	85	47	101
Charge offs		(64)	(48)	(102)	(115)
Recoveries		15	13	23	32
Net (charge offs) recoveries		(49)	(35)	(79)	(83)
Balance at end of period		648	624	648	624
Ending balance: collectively evaluated for impairment						$ 598		$ 550
Ending balance: individually evaluated for impairment						50		74
Total allowances for credit losses		703	574	680	606	648	$ 680	624
Collectively evaluated for impairment						81,540		70,098
Individually evaluated for impairment	[1]					513		508
Loans carried at the lower of amortized cost or fair value less cost to sell						1,564		1,592
Total loans						83,617	77,741	72,198
Commercial Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans						63,596	58,087
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		90	93	89	108
Provision for credit losses		(3)	6	(1)	8
Charge offs		(1)	(5)	(2)	(24)
Recoveries		3	0	3	2
Net (charge offs) recoveries		2	(5)	1	(22)
Balance at end of period		89	94	89	94
Ending balance: collectively evaluated for impairment						86		90
Ending balance: individually evaluated for impairment						3		4
Total allowances for credit losses		90	93	89	108	89	89	94
Collectively evaluated for impairment						11,388		9,469
Individually evaluated for impairment	[1]					132		213
Loans carried at the lower of amortized cost or fair value less cost to sell						0		0
Total loans						11,520	10,300	9,682
Commercial Loans [Member] | Business and Corporate Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		295	129	275	112
Provision for credit losses		(2)	56	22	75
Charge offs		(38)	(6)	(44)	(11)
Recoveries		5	1	7	4
Net (charge offs) recoveries		(33)	(5)	(37)	(7)
Balance at end of period		260	180	260	180
Ending balance: collectively evaluated for impairment						257		172
Ending balance: individually evaluated for impairment						3		8
Total allowances for credit losses		295	129	275	112	260	275	180
Collectively evaluated for impairment						19,624		15,913
Individually evaluated for impairment	[1]					88		43
Loans carried at the lower of amortized cost or fair value less cost to sell						0		0
Total loans						19,712	17,819	15,956
Commercial Loans [Member] | Global Banking [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		128	67	107	68
Provision for credit losses		2	29	23	36
Charge offs		0	0	0	(8)
Recoveries		0	0	0	0
Net (charge offs) recoveries		0	0	0	(8)
Balance at end of period		130	96	130	96
Ending balance: collectively evaluated for impairment						130		96
Ending balance: individually evaluated for impairment						0		0
Total allowances for credit losses		128	67	107	68	130	107	96
Collectively evaluated for impairment						28,929		24,268
Individually evaluated for impairment	[1]					13		0
Loans carried at the lower of amortized cost or fair value less cost to sell						0		0
Total loans						28,942	26,387	24,268
Commercial Loans [Member] | Other Commercial [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		21	19	21	20
Provision for credit losses		(3)	(9)	(2)	(13)
Charge offs		0	0	(1)	0
Recoveries		0	3	0	6
Net (charge offs) recoveries		0	3	(1)	6
Balance at end of period		18	13	18	13
Ending balance: collectively evaluated for impairment						17		11
Ending balance: individually evaluated for impairment						1		2
Total allowances for credit losses		21	19	21	20	18	21	13
Collectively evaluated for impairment						3,415		3,117
Individually evaluated for impairment	[1]					7		10
Loans carried at the lower of amortized cost or fair value less cost to sell						0		0
Total loans						3,422	3,581	3,127
Consumer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Total loans						20,021	19,654
Consumer Loans [Member] | Residential Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		95	156	107	186
Provision for credit losses		(6)	7	(6)	(9)
Charge offs		(10)	(19)	(24)	(36)
Recoveries		4	5	6	8
Net (charge offs) recoveries		(6)	(14)	(18)	(28)
Balance at end of period		83	149	83	149
Ending balance: collectively evaluated for impairment						42		93
Ending balance: individually evaluated for impairment						41		56
Total allowances for credit losses		95	156	107	186	83	107	149
Collectively evaluated for impairment						15,478		14,355
Individually evaluated for impairment	[1]					262		215
Loans carried at the lower of amortized cost or fair value less cost to sell						1,493		1,527
Total loans						17,233	16,661	16,097
Consumer Loans [Member] | Home Equity Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		29	52	32	49
Provision for credit losses		0	(8)	(2)	(6)
Charge offs		(3)	(3)	(5)	(8)
Recoveries		1	1	2	7
Net (charge offs) recoveries		(2)	(2)	(3)	(1)
Balance at end of period		27	42	27	42
Ending balance: collectively evaluated for impairment						26		40
Ending balance: individually evaluated for impairment						1		2
Total allowances for credit losses		29	52	32	49	27	32	42
Collectively evaluated for impairment						1,610		1,830
Individually evaluated for impairment	[1]					5		19
Loans carried at the lower of amortized cost or fair value less cost to sell						71		65
Total loans						1,686	1,784	1,914
Consumer Loans [Member] | Credit Cards [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		35	45	39	50
Provision for credit losses		4	4	7	9
Charge offs		(8)	(12)	(16)	(23)
Recoveries		2	2	3	3
Net (charge offs) recoveries		(6)	(10)	(13)	(20)
Balance at end of period		33	39	33	39
Ending balance: collectively evaluated for impairment						32		37
Ending balance: individually evaluated for impairment						1		2
Total allowances for credit losses		35	45	39	50	33	39	39
Collectively evaluated for impairment						686		673
Individually evaluated for impairment	[1]					6		8
Loans carried at the lower of amortized cost or fair value less cost to sell						0		0
Total loans						692	720	681
Consumer Loans [Member] | Other consumer [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		10	13	10	13
Provision for credit losses		2	0	6	1
Charge offs		(4)	(3)	(10)	(5)
Recoveries		0	1	2	2
Net (charge offs) recoveries		(4)	(2)	(8)	(3)
Balance at end of period		8	11	8	11
Ending balance: collectively evaluated for impairment						8		11
Ending balance: individually evaluated for impairment						0		0
Total allowances for credit losses		$ 10	$ 13	$ 10	$ 13	8	10	11
Collectively evaluated for impairment						410		473
Individually evaluated for impairment	[1]					0		0
Loans carried at the lower of amortized cost or fair value less cost to sell						0		0
Total loans						$ 410	$ 489	$ 473

[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 $775 million and $725 million at June 30, 2015 and 2014, respectively.