Related Party Transactions - Additional Information (Details) - USD ($)	9 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Long-term debt	$ 20,048,000,000	$ 26,697,000,000
Notional value of derivative contracts	3,074,468,000,000	4,807,851,000,000
Preferred stock issued	1,265,000,000	1,265,000,000
HNAH [Member]
Related Party Transaction [Line Items]
Long-term debt	2,900,000,000	7,800,000,000
Maximum borrowing capacity	4,000,000,000.0	150,000,000
Amount outstanding under the loan agreement	0	0
Preferred stock issued	1,265,000,000	1,265,000,000
Preferred stock outstanding	1,265,000,000	1,265,000,000
HMUS [Member]
Related Party Transaction [Line Items]
Extended loans and lines of credit	12,000,000,000.0	12,000,000,000.0
Amount outstanding on line of credit	1,100,000,000	2,300,000,000
Loans and leases receivable from related parties	1,088,000,000	2,296,000,000
Other HSBC affiliates [Member]
Related Party Transaction [Line Items]
Extended loans and lines of credit	3,400,000,000	3,400,000,000
Amount outstanding on line of credit	0	0
Loans and leases receivable from related parties	92,000,000	47,000,000
HSBC Affiliates [Member]
Related Party Transaction [Line Items]
Long-term debt	2,866,000,000	7,848,000,000
Loans and leases receivable from related parties	1,180,000,000	2,343,000,000
Notional value of derivative contracts	862,700,000,000	1,111,500,000,000
Fair value of derivative assets and liabilities	491,000,000	$ 90,000,000
Floating Rate Note Maturing May 2025 [Member] \| HNAH [Member] \| Subordinated Debt [Member]
Related Party Transaction [Line Items]
Long-term debt	900,000,000
Fixed Rate Note Maturing September 2025 [Member] \| HNAH [Member] \| Senior debt [Member]
Related Party Transaction [Line Items]
Long-term debt	2,000,000,000.0
Deposits [Member]
Related Party Transaction [Line Items]
Fixed-rate senior debt obligations recharacterized as time deposits	5,000,000,000.0
Deposits [Member] \| Fixed Rate Note Maturing March 2021 [Member]
Related Party Transaction [Line Items]
Fixed-rate senior debt obligations recharacterized as time deposits	1,500,000,000
Deposits [Member] \| Fixed Rate Note Maturing May 2021 [Member]
Related Party Transaction [Line Items]
Fixed-rate senior debt obligations recharacterized as time deposits	2,000,000,000.0
Deposits [Member] \| Fixed Rate Note Maturing March 2026 [Member]
Related Party Transaction [Line Items]
Fixed-rate senior debt obligations recharacterized as time deposits	$ 1,500,000,000

Debt Obligations Recharacterized as Time Deposits

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- Definition

Loan and lease receivable extended loan and line of credit facility.

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No definition available.

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Loan and lease receivable revolving line of credit outstanding.

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

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Nominal or face amount used to calculate payment on derivative.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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- Definition

For an unclassified balance sheet, reflects the carrying amount of unpaid loan amounts due from related parties at the balance sheet date.

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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- Definition

Aggregate par or stated value of issued nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable preferred shares, par value and other disclosure concepts are in another section within stockholders' equity.

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Value of all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by shareholders, which is net of related treasury stock. May be all or a portion of the number of preferred shares authorized. These shares represent the ownership interest of the preferred shareholders.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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