Loans - Summary of Past Due Status of Loans (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	$ 492		$ 588
Days Past Due, 90 + days	1,025		1,229
Total Days Past Due, 30 Days or More	1,517		1,817
Current	71,922	[1]	65,878	[1]
Total loans	73,439		67,695		67,710
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	53		89
Days Past Due, 90 + days	37		106
Total Days Past Due, 30 Days or More	90		195
Current	53,972	[1]	48,299	[1]
Total loans	54,062		48,494
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	4		6
Days Past Due, 90 + days	11		58
Total Days Past Due, 30 Days or More	15		64
Current	9,646	[1]	8,970	[1]
Total loans	9,661		9,034		8,919
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	24		48
Days Past Due, 90 + days	20		36
Total Days Past Due, 30 Days or More	44		84
Current	17,311	[1]	14,362	[1]
Total loans	17,355		14,446		13,668
Commercial Loans [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 Days Past Due, 30 Days or More	0		11
Current	24,001	[1]	21,614	[1]
Total loans	24,001		21,625		23,370
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	25		27
Days Past Due, 90 + days	6		9
Total Days Past Due, 30 Days or More	31		36
Current	3,014	[1]	3,353	[1]
Total loans	3,045		3,389		2,552
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	439		499
Days Past Due, 90 + days	988		1,123
Total Days Past Due, 30 Days or More	1,427		1,622
Current	17,950	[1]	17,579	[1]
Total loans	19,377		19,201
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	399		443
Days Past Due, 90 + days	913		1,037
Total Days Past Due, 30 Days or More	1,312		1,480
Current	15,090	[1]	14,346	[1]
Total loans	16,402		15,826		15,720
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	19		28
Days Past Due, 90 + days	55		59
Total Days Past Due, 30 Days or More	74		87
Current	1,750	[1]	1,924	[1]
Total loans	1,824		2,011		2,087
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	11		16
Days Past Due, 90 + days	10		14
Total Days Past Due, 30 Days or More	21		30
Current	665	[1]	824	[1]
Total loans	686		854		856
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 Days Past Due, 30 Days or More	20		25
Current	445	[1]	485	[1]
Total loans	$ 465		$ 510		$ 538

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