Loans - Summary of Past Due Status of Loans (Detail) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2016		Dec. 31, 2015		Jun. 30, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		$ 1,040		$ 1,407
Current	[1]	78,770		81,510
Total loans		79,810		82,917		$ 83,617
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		182		131
Current	[1]	59,361		62,322
Total loans		59,543		62,453
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		80		64
Current	[1]	10,893		9,936
Total loans		10,973		10,000		11,520
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		91		61
Current	[1]	18,984		19,055
Total loans		19,075		19,116		19,712
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]	26,357		29,969
Total loans		26,357	[2]	29,969	[2]	28,942
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		11		6
Current	[1]	3,127		3,362
Total loans		3,138		3,368		3,422
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		858		1,276
Current	[1]	19,409		19,188
Total loans		20,267		20,464
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		774	[3]	1,178
Current	[1]	16,893	[3]	16,580
Total loans		17,667	[3],[4]	17,758		17,233
Transfer of loans to held-for-sale	[3]	369
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		55		65
Current	[1]	1,456		1,535
Total loans		1,511		1,600		1,686
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		17		19
Current	[1]	651		680
Total loans		668		699		692
Consumer Loans [Member] | Other consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Days Past Due, 30 Days or More		12		14
Current	[1]	409		393
Total loans		421		407		$ 410
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		566		496
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		144		67
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		51		31
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		88		36
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		5		0
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		422		429
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	[3]	397
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		11		15
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		8		10
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		6		7
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		474		911
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		38		64
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		29		33
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		3		25
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		436		847
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		377	[3]	781
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		44		50
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		9
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		$ 6		$ 7

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

[2] Represents large multinational firms including globally focused U.S. corporate and financial institutions and U.S. dollar lending to multinational banking customers managed by HSBC on a global basis. Also includes loans to HSBC affiliates which totaled $5,072 million and $4,815 million at June 30, 2016 and December 31, 2015, respectively. See Note 14, "Related Party Transactions," for additional information regarding loans to HSBC affiliates.

[3] The decrease in past due loans at June 30, 2016 reflects the impact of the transfer of certain residential mortgage loans with a carrying value of $369 million to held for sale during the first half of 2016. See Note 6, "Loans Held for Sale," for additional details.

[4] The decrease in nonaccrual loans at June 30, 2016 reflects the impact of the transfer of certain residential mortgage loans with a carrying value of $369 million to held for sale during the first half of 2016.