Loans - Status of Commercial Loan Portfolio (Detail) - USD ($) $ in Millions	Mar. 31, 2016		Dec. 31, 2015		Mar. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Accruing Loans Contractually Past Due 90 days or More	$ 17		$ 17
Total loans	81,732		82,917		$ 81,458
Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	61,108		62,187
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest	503		265
Accruing Loans Contractually Past Due 90 days or More	1		1
Total loans	61,612		62,453
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	10,117		9,947
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest	53		53
Accruing Loans Contractually Past Due 90 days or More	0		0
Total loans	10,170		10,000		10,901
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	19,212		18,948
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest	199		167
Accruing Loans Contractually Past Due 90 days or More	1		1
Total loans	19,412		19,116		19,251
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	28,716		29,925
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest	250		44
Accruing Loans Contractually Past Due 90 days or More	0		0
Total loans	28,966	[1]	29,969	[1]	28,029
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	3,063		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	$ 3,064		$ 3,368		$ 3,466

[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 $5,107 million and $4,815 million at March 31, 2016 and December 31, 2015, respectively. See Note 14, "Related Party Transactions," for additional information regarding loans to HSBC affiliates.