Related Party Transactions - Narrative (Details) - USD ($)		3 Months Ended	12 Months Ended
		Sep. 30, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Long-term debt	[1]		$ 18,661,000,000	$ 17,591,000,000
Loans receivable from related parties	[1]		58,987,000,000	59,380,000,000
Notional value of derivative contracts			1,301,082,000,000	1,327,929,000,000
Proceeds from sale of trading assets			10,000,000	0	$ 0
Preferred stock issued			265,000,000	265,000,000
Preferred stock outstanding			265,000,000	265,000,000
Return of capital to parent			0	2,000,000,000	$ 1,000,000,000
HNAH
Related Party Transaction [Line Items]
Return of capital to parent			1,500,000,000
HNAH
Related Party Transaction [Line Items]
Long-term debt			6,500,000,000	6,000,000,000
Maximum borrowing capacity			4,000,000,000
Amount outstanding under the loan agreement			0	0
Preferred stock issued			265,000,000	265,000,000
Preferred stock outstanding			265,000,000	265,000,000
HNAH | Loans And Lines Of Credit
Related Party Transaction [Line Items]
Loans receivable from related parties			1,300,000,000	1,250,000,000
HNAH | Loans And Lines Of Credit Maturing In May 2024
Related Party Transaction [Line Items]
Loans receivable from related parties			1,000,000,000
HNAH | Loans And Lines Of Credit Maturing In July 2024
Related Party Transaction [Line Items]
Loans receivable from related parties			300,000,000
HMUS | Loans And Lines Of Credit
Related Party Transaction [Line Items]
Extended loans and lines of credit			13,300,000,000	12,800,000,000
Loans receivable from related parties			1,318,000,000	2,243,000,000
Other HSBC affiliates | Loans And Lines Of Credit
Related Party Transaction [Line Items]
Extended loans and lines of credit			3,900,000,000
Loans receivable from related parties			0	0
Other HSBC affiliates | Short Term Lending
Related Party Transaction [Line Items]
Loans receivable from related parties			0	64,000,000
Related Party
Related Party Transaction [Line Items]
Long-term debt			6,511,000,000	6,011,000,000
Loans receivable from related parties			2,618,000,000	3,557,000,000
Notional value of derivative contracts			719,600,000,000	789,200,000,000
Fair value of derivative assets and liabilities			29,000,000	$ 24,000,000
Affiliated Entity
Related Party Transaction [Line Items]
Increase to additional paid-in-capital		$ 8,000,000
Proceeds from sale of trading assets		$ 900,000,000
Fixed Rate Note Maturing June 2025 | HNAH | Senior debt:
Related Party Transaction [Line Items]
Long-term debt			2,000,000,000
Fixed Rate Note Maturing September 2025 | HNAH | Senior debt:
Related Party Transaction [Line Items]
Long-term debt			2,000,000,000
Fixed Rate Note Maturing December 2027 | HNAH | Senior debt:
Related Party Transaction [Line Items]
Long-term debt			500,000,000
Fixed Rate Note Maturing June 2030 | HNAH | Senior debt:
Related Party Transaction [Line Items]
Long-term debt			1,500,000,000
Fixed Rate Note Maturing December 2028 | HNAH | Senior debt:
Related Party Transaction [Line Items]
Long-term debt			$ 500,000,000

[1] The following table summarizes assets and liabilities related to our consolidated variable interest entities ("VIEs") at December 31, 2023 and 2022. Assets and liabilities exclude intercompany balances that eliminate in consolidation. See Note 27, "Variable Interest Entities," for additional information. At December 31,20232022(in millions)AssetsLoans, net$— $162 Other assets23 44 Total assets$23 $206 LiabilitiesInterest, taxes and other liabilities$17 $22 Total liabilities$17 $22