Loans - Summary of Past Due Status of Loans (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013		Jun. 30, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	$ 479		$ 588
Days Past Due, 90 + days	1,051		1,229
Total Past Due	1,530		1,817
Current	70,668	[1]	65,878	[1]
Total loans	72,198		67,695		66,705
Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	41		89
Days Past Due, 90 + days	41		106
Total Past Due	82		195
Current	52,951	[1]	48,299	[1]
Total loans	53,033		48,494
Commercial Loan [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	7		6
Days Past Due, 90 + days	14		58
Total Past Due	21		64
Current	9,661	[1]	8,970	[1]
Total loans	9,682		9,034		8,529
Commercial Loan [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	7		48
Days Past Due, 90 + days	27		36
Total Past Due	34		84
Current	15,922	[1]	14,362	[1]
Total loans	15,956		14,446		12,391
Commercial Loan [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	0		8
Days Past Due, 90 + days	0		3
Total Past Due	0		11
Current	24,268	[1]	21,614	[1]
Total loans	24,268		21,625		23,339
Commercial Loan [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	27		27
Days Past Due, 90 + days	0		9
Total Past Due	27		36
Current	3,100	[1]	3,353	[1]
Total loans	3,127		3,389		3,005
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	438		499
Days Past Due, 90 + days	1,010		1,123
Total Past Due	1,448		1,622
Current	17,717	[1]	17,579	[1]
Total loans	19,165		19,201
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	400		443
Days Past Due, 90 + days	935		1,037
Total Past Due	1,335		1,480
Current	14,762	[1]	14,346	[1]
Total loans	16,097		15,826		15,837
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	18		28
Days Past Due, 90 + days	54		59
Total Past Due	72		87
Current	1,842	[1]	1,924	[1]
Total loans	1,914		2,011		2,172
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	10		16
Days Past Due, 90 + days	11		14
Total Past Due	21		30
Current	660	[1]	824	[1]
Total loans	681		854		858
Consumer Loans [Member] | Other consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	10		12
Days Past Due, 90 + days	10		13
Total Past Due	20		25
Current	453	[1]	485	[1]
Total loans	$ 473		$ 510		$ 574

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