Loans - Components of Loans (Details) - USD ($) $ in Millions	Jun. 30, 2019		Dec. 31, 2018		Jun. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 72,478		$ 68,978		$ 66,399
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	52,745		49,342
Commercial Loans [Member] | Real Estate, Including Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	11,704		11,344		11,245
Commercial Loans [Member] | Business and Corporate Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	14,310		13,066		12,109
Commercial Loans [Member] | Global Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	20,896	[1]	20,167	[1]	18,877
Commercial Loans [Member] | Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,835	[2]	4,765	[2]	4,612
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	19,733		19,636
Consumer Loans [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	17,421		17,383		17,326
Consumer Loans [Member] | Home Equity Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	911		982		1,086
Consumer Loans [Member] | Credit Cards [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,129		1,019		841
Consumer Loans [Member] | Other consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	272		252		303
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 3,096		$ 2,274		$ 1,895

[1] 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] Includes loans to HSBC affiliates which totaled $3,096 million and $2,274 million at June 30, 2019 and December 31, 2018, respectively. See Note 14, "Related Party Transactions," for additional information regarding loans to HSBC affiliates.