Loans - Summary of Past Due Status of Loans (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012		Jun. 30, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	$ 662		$ 760
Days Past Due, 90 + days	1,180		1,367
Total Past Due	1,842		2,127
Current	64,863	[1]	61,131	[1]
Total loans	66,705		63,258		56,064
Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	124		208
Days Past Due, 90 + days	101		261
Total Past Due	225		469
Current	47,039	[1]	43,681	[1]
Total loans	47,264		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	79		89
Days Past Due, 90 + days	38		152
Total Past Due	117		241
Current	8,412	[1]	8,216	[1]
Total loans	8,529		8,457		7,977
Commercial Loan [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	25		73
Days Past Due, 90 + days	39		70
Total Past Due	64		143
Current	12,327	[1]	12,465	[1]
Total loans	12,391		12,608		11,256
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	8		8
Total Past Due	8		38
Current	23,331	[1]	19,971	[1]
Total loans	23,339		20,009		15,042
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	20		16
Days Past Due, 90 + days	16		31
Total Past Due	36		47
Current	2,969	[1]	3,029	[1]
Total loans	3,005		3,076		3,142
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	538		552
Days Past Due, 90 + days	1,079		1,106
Total Past Due	1,617		1,658
Current	17,824	[1]	17,450	[1]
Total loans	19,441		19,108
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	37		40
Days Past Due, 90 + days	64		82
Total Past Due	101		122
Current	2,071	[1]	2,202	[1]
Total loans	2,172		2,324		2,455
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	487		493
Days Past Due, 90 + days	978		976
Total Past Due	1,465		1,469
Current	14,372	[1]	13,902	[1]
Total loans	15,837		15,371		14,758
Consumer Loans [Member] | Credit Card Receivables [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	11		14
Days Past Due, 90 + days	11		15
Total Past Due	22		29
Current	836	[1]	786	[1]
Total loans	858		815		783
Consumer Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	3		5
Days Past Due, 90 + days	26		33
Total Past Due	29		38
Current	545	[1]	560	[1]
Total loans	$ 574		$ 598		$ 651

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