Loans - Components of Loans (Details) - USD ($) $ in Millions		Mar. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		$ 61,526	$ 62,088
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		41,152	41,599
Commercial Loans [Member] | Real Estate, Including Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		10,087	10,464
Commercial Loans [Member] | Business and Corporate Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	[1]	13,125	13,479
Loans funded under the Payroll Protection Program		1,294	1,043
Commercial Loans [Member] | Global Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	[2]	13,157	13,519
Commercial Loans [Member] | Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		4,783	4,137
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		20,374	20,489
Consumer Loans [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		18,425	18,377
Consumer Loans [Member] | Home Equity Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		698	727
Consumer Loans [Member] | Credit Cards [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		937	1,066
Consumer Loans [Member] | Other consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	[3]	314	319
Consumer Loans [Member] | Student Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, designated under fair value option		30	32
Affiliated Entity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		1,652	1,100
Affiliated Entity [Member] | Commercial Loans [Member] | Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	[4]	1,652	1,100
Other [Member] | Commercial Loans [Member] | Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		$ 3,131	$ 3,037

[1] Includes loans funded under the Paycheck Protection Program ("PPP") which totaled $1,294 million and $1,043 million at March 31, 2021 and December 31, 2020, respectively. PPP loans are fully guaranteed by the Small Business Administration, if certain conditions are met.

[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] Includes certain student loans that we have elected to designate under the fair value option and are therefore carried at fair value, which totaled $30 million and $32 million at March 31, 2021 and December 31, 2020, respectively. See Note 10, "Fair Value Option," for further details.

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