Loans - Components of Loans (Details) - USD ($) $ in Millions		Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		$ 81,728	$ 68,553
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		61,246	48,211
Commercial Loans [Member] | Real Estate, Including Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		11,369	11,501
Commercial Loans [Member] | Business and Corporate Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		19,620	13,479
Commercial Loans [Member] | Global Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	[1]	24,141	17,915
Commercial Loans [Member] | Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		6,116	5,316
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		20,482	20,342
Consumer Loans [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		18,034	17,801
Consumer Loans [Member] | Home Equity Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		814	853
Consumer Loans [Member] | Credit Cards [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		1,300	1,405
Consumer Loans [Member] | Other consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	[2]	334	283
Consumer Loans [Member] | Student Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, designated under fair value option		37
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		3,087	2,343
Affiliated Entity [Member] | Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	[3]		2,343
Affiliated Entity [Member] | Commercial Loans [Member] | Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	[3]	3,087
Other [Member] | Commercial Loans [Member] | Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		$ 3,029	$ 2,973

[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 certain student loans that we have elected to designate under the fair value option and are therefore carried at fair value, which totaled $37 million at March 31, 2020. See Note 10, "Fair Value Option," for further details.

[3] See Note 14, "Related Party Transactions," for additional information regarding loans to HSBC affiliates.