Loans - Summary of Past Due Status of Loans (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	$ 581		$ 760
Days Past Due, 90 + days	1,268		1,367
Total Past Due	1,849		2,127
Current	65,861	[1]	61,131	[1]
Total loans	67,710		63,258		61,452
Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	73		208
Days Past Due, 90 + days	124		261
Total Past Due	197		469
Current	48,312	[1]	43,681	[1]
Total loans	48,509		44,150
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	3		89
Days Past Due, 90 + days	58		152
Total Past Due	61		241
Current	8,858	[1]	8,216	[1]
Total loans	8,919		8,457		7,920
Commercial Loan [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	42		73
Days Past Due, 90 + days	35		70
Total Past Due	77		143
Current	13,591	[1]	12,465	[1]
Total loans	13,668		12,608		12,497
Commercial Loan [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	0		30
Days Past Due, 90 + days	4		8
Total Past Due	4		38
Current	23,366	[1]	19,971	[1]
Total loans	23,370		20,009		19,011
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	28		16
Days Past Due, 90 + days	27		31
Total Past Due	55		47
Current	2,497	[1]	3,029	[1]
Total loans	2,552		3,076		3,140
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	508		552
Days Past Due, 90 + days	1,144		1,106
Total Past Due	1,652		1,658
Current	17,549	[1]	17,450	[1]
Total loans	19,201		19,108
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	457		493
Days Past Due, 90 + days	1,043		976
Total Past Due	1,500		1,469
Current	14,220	[1]	13,902	[1]
Total loans	15,720		15,371		15,086
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	29		40
Days Past Due, 90 + days	64		82
Total Past Due	93		122
Current	1,994	[1]	2,202	[1]
Total loans	2,087		2,324		2,387
Consumer Loans [Member] | Credit Card Receivables [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	15		14
Days Past Due, 90 + days	13		15
Total Past Due	28		29
Current	828	[1]	786	[1]
Total loans	856		815		796
Consumer Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	7		5
Days Past Due, 90 + days	24		33
Total Past Due	31		38
Current	507	[1]	560	[1]
Total loans	$ 538		$ 598		$ 615

[1] Loans less than 30 days past due are presented as current.