Loans - Components of Loans (Details) - USD ($) $ in Millions	Sep. 30, 2017		Dec. 31, 2016		Sep. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 67,593		$ 73,875		$ 77,625
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	48,128		54,216
Commercial Loans [Member] | Real Estate, Including Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	10,442		10,890		10,958
Commercial Loans [Member] | Business and Corporate Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	13,328		14,080		14,057	[1]
Commercial Loans [Member] | Global Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	19,950	[2],[3]	23,481	[2],[3]	25,559	[1]
Commercial Loans [Member] | Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,408	[2]	5,765	[2]	7,458
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	19,465		19,659
Consumer Loans [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	17,196		17,181		17,091
Consumer Loans [Member] | Home Equity Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,234		1,408		1,454
Consumer Loans [Member] | Credit Cards [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	656		688		668
Consumer Loans [Member] | Other consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 379		$ 382		$ 380

[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 14, "Business Segments." As a result, we reclassified $3.6 billion of loans and $21 million of allowance for credit losses from business and corporate banking to global banking at September 30, 2016 to conform with the current year presentation

[2] During the first quarter of 2017, in conjunction with the creation of the new Corporate Center segment as discussed further in Note 14, "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 $1,820 million and $3,274 million at September 30, 2017 and December 31, 2016, respectively. All tables below have been restated to reflect this reclassification, as applicable. See Note 13, "Related Party Transactions," for additional information regarding loans to HSBC affiliates.

[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.