Loans - Summary of Past Due Status of Loans (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	$ 503		$ 588
Days Past Due, 90 + days	1,043		1,229
Total Days Past Due, 30 Days or More	1,546		1,817
Current	76,195	[1]	65,878	[1]
Total loans	77,741		67,695		63,258
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	72		89
Days Past Due, 90 + days	37		106
Total Days Past Due, 30 Days or More	109		195
Current	57,978	[1]	48,299	[1]
Total loans	58,087		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	25		6
Days Past Due, 90 + days	22		58
Total Days Past Due, 30 Days or More	47		64
Current	10,253	[1]	8,970	[1]
Total loans	10,300		9,034		8,457
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	32		48
Days Past Due, 90 + days	9		36
Total Days Past Due, 30 Days or More	41		84
Current	17,778	[1]	14,362	[1]
Total loans	17,819		14,446		12,608
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	26,387	[1]	21,614	[1]
Total loans	26,387		21,625		20,009
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	15		27
Days Past Due, 90 + days	6		9
Total Days Past Due, 30 Days or More	21		36
Current	3,560	[1]	3,353	[1]
Total loans	3,581		3,389		3,076
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	431		499
Days Past Due, 90 + days	1,006		1,123
Total Days Past Due, 30 Days or More	1,437		1,622
Current	18,217	[1]	17,579	[1]
Total loans	19,654		19,201
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	390		443
Days Past Due, 90 + days	931		1,037
Total Days Past Due, 30 Days or More	1,321		1,480
Current	15,340	[1]	14,346	[1]
Total loans	16,661		15,826		15,371
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	21		28
Days Past Due, 90 + days	56		59
Total Days Past Due, 30 Days or More	77		87
Current	1,707	[1]	1,924	[1]
Total loans	1,784	[2]	2,011		2,324
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	699	[1]	824	[1]
Total loans	720	[3]	854		815
Consumer Loans [Member] | Other consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due, 30-89 days	9		12
Days Past Due, 90 + days	9		13
Total Days Past Due, 30 Days or More	18		25
Current	471	[1]	485	[1]
Total loans	$ 489		$ 510		$ 598

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

[2] Home equity mortgage maturities reflect estimates based on historical payment patterns.

[3] As credit card receivables do not have stated maturities, the table reflects estimates based on historical payment patterns.