Loans - Status of Commercial Loan Portfolio (Detail) - USD ($) $ in Millions	Jun. 30, 2017		Dec. 31, 2016		Jun. 30, 2016
Financing Receivable, Recorded Investment [Line Items]
Accruing Loans Contractually Past Due 90 days or More	$ 15		$ 18
Total loans	68,063		73,875		$ 79,810
Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	47,812		53,425
Nonaccrual Loans	775		790
Accruing Loans Contractually Past Due 90 days or More	1		1
Total loans	48,588		54,216
Commercial Loans [Member] | Real Estate, Including Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	10,190		10,834
Nonaccrual Loans	50		56
Accruing Loans Contractually Past Due 90 days or More	0		0
Total loans	10,240		10,890		10,973
Commercial Loans [Member] | Business and Corporate Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	12,679		13,892
Nonaccrual Loans	188		187
Accruing Loans Contractually Past Due 90 days or More	1		1
Total loans	12,868		14,080		14,636	[1]
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	20,510		22,935
Nonaccrual Loans	537		546
Accruing Loans Contractually Past Due 90 days or More	0		0
Total loans	21,047	[2],[3]	23,481	[2],[3]	25,724	[1]
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans	4,433		5,764
Nonaccrual Loans	0		1
Accruing Loans Contractually Past Due 90 days or More	0		0
Total loans	$ 4,433	[3]	$ 5,765	[3]	$ 8,210

[1] During the fourth quarter of 2016, we transferred certain client relationships from Commercial Banking to Global Banking and Markets as discussed further in Note 13, "Business Segments." As a result, we reclassified $4.4 billion of loans and $27 million of allowance for credit losses from business and corporate banking to global banking at June 30, 2016 to conform with the current year presentation

[2] Represents large multinational firms including globally focused U.S. corporate and financial institutions, U.S. dollar lending to multinational banking clients managed by HSBC on a global basis and complex large business clients supported by Global Banking and Markets relationship managers.

[3] Represents large multinational firms including globally focused U.S. corporate and financial institutions, U.S. dollar lending to multinational banking clients managed by HSBC on a global basis and complex large business clients supported by Global Banking and Markets relationship managers. (2)During the first quarter of 2017, in conjunction with the creation of the new Corporate Center segment as discussed further in Note 13, "Business Segments," we reclassified loans to HSBC affiliates from global banking to other commercial and revised the prior period to conform with the current year presentation. As a result, other commercial includes loans to HSBC affiliates which totaled $1,423 million and $3,274 million at June 30, 2017 and December 31, 2016, respectively. All tables below have been restated to reflect this reclassification, as applicable. See Note 12, "Related Party Transactions," for additional information regarding loans to HSBC affiliates.