Loans - Summary of Past Due Status of Loans (Detail) - USD ($) $ in Millions		Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		$ 1,407		$ 1,546
Current	[1]	81,510		76,195
Total loans		82,917		77,741	$ 67,695
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		131		109
Current	[1]	62,322		57,978
Total loans		62,453		58,087
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		64		47
Current	[1]	9,936		10,253
Total loans		10,000		10,300	9,034
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		61		41
Current	[1]	19,055		17,778
Total loans		19,116		17,819	14,446
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		0		0
Current	[1]	29,969		26,387
Total loans		29,969		26,387	21,625
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		6		21
Current	[1]	3,362		3,560
Total loans		3,368		3,581	3,389
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		1,276		1,437
Current	[1]	19,188		18,217
Total loans		20,464		19,654
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		1,178		1,321
Current	[1]	16,580		15,340
Total loans		17,758		16,661	15,826
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		65		77
Current	[1]	1,535		1,707
Total loans		1,600	[2]	1,784	2,011
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		19		21
Current	[1]	680		699
Total loans		699	[3]	720	854
Consumer Loans [Member] | Other consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		14		18
Current	[1]	393		471
Total loans		407		489	$ 510
Financing Receivables, 30 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		496		503
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		67		72
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		31		25
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		36		32
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		0		0
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		0		15
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		429		431
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		397		390
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		15		21
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		10		11
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer Loans [Member] | Other consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		7		9
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		911		1,043
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		64		37
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		33		22
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		25		9
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		0		0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		6		6
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		847		1,006
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		781		931
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		50		56
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		9		10
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Loans [Member] | Other consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		$ 7		$ 9

[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.