Loans - Credit Risk Profile of Commercial Loans (Detail) - USD ($) $ in Millions		Sep. 30, 2016		Dec. 31, 2015		Sep. 30, 2015
Financing Receivable, Recorded Investment [Line Items]
Total loans		$ 77,625		$ 82,917		$ 84,942
Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans		58,032		62,453
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans		10,958		10,000		12,096
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans		17,665		19,116		19,514
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans		26,414	[1]	29,969	[1]	29,808
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans		2,995		3,368		$ 3,334
Internal Investment Grade [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	36,703		43,854
Internal Investment Grade [Member] | Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	8,273		8,487
Internal Investment Grade [Member] | Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	8,561		10,373
Internal Investment Grade [Member] | Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	17,904		23,111
Internal Investment Grade [Member] | Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	[2]	1,965		1,883
Internal Noninvestment Grade [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans		21,329		18,599
Internal Noninvestment Grade [Member] | Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans		2,685		1,513
Internal Noninvestment Grade [Member] | Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans		9,104		8,743
Internal Noninvestment Grade [Member] | Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans		8,510		6,858
Internal Noninvestment Grade [Member] | Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans		$ 1,030		$ 1,485

[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.

[2] Investment grade includes commercial loans with credit ratings of at least BBB- or above or the equivalent based on our internal credit rating system.