Loans - Status of Commercial Loan Portfolio (Detail) - USD ($) $ in Millions	Sep. 30, 2016		Dec. 31, 2015		Sep. 30, 2015
Financing Receivable, Recorded Investment [Line Items]
Accruing Loans Contractually Past Due 90 days or More	$ 17		$ 17
Total loans	77,625		82,917		$ 84,942
Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	57,183		62,187
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest	848		265
Accruing Loans Contractually Past Due 90 days or More	1		1
Total loans	58,032		62,453
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	10,934		9,947
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest	24		53
Accruing Loans Contractually Past Due 90 days or More	0		0
Total loans	10,958		10,000		12,096
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	17,462		18,948
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest	202		167
Accruing Loans Contractually Past Due 90 days or More	1		1
Total loans	17,665		19,116		19,514
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	25,793		29,925
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest	621		44
Accruing Loans Contractually Past Due 90 days or More	0		0
Total loans	26,414	[1]	29,969	[1]	29,808
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	2,994		3,367
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest	1		1
Accruing Loans Contractually Past Due 90 days or More	0		0
Total loans	$ 2,995		$ 3,368		$ 3,334

[1] 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 $4,463 million and $4,815 million at September 30, 2016 and December 31, 2015, respectively. See Note 14, "Related Party Transactions," for additional information regarding loans to HSBC affiliates.