Related Party Transactions - Additional Information (Details) - USD ($)	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Related Party Transaction [Line Items]
Long-term debt	$ 31,475,000,000		$ 30,628,000,000
Derivative, notional amount	5,512,901,000,000		5,556,668,000,000
Preferred stock issued	1,265,000,000		1,265,000,000
Return of capital to parent	2,400,000,000	$ 0
HNAH [Member]
Related Party Transaction [Line Items]
Long-term debt	7,800,000,000		7,800,000,000
Maximum borrowing capacity	150,000,000		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
Return of capital to parent	2,400,000,000
HMUS [Member]
Related Party Transaction [Line Items]
Extended loans and lines of credit	12,800,000,000		12,800,000,000
Loans and leases receivable from related parties	2,360,000,000		2,235,000,000
Amount outstanding on line of credit	2,400,000,000		2,200,000,000
HSBC Bank Canada [Member]
Related Party Transaction [Line Items]
Extended loans and lines of credit	500,000,000		500,000,000
Loans and leases receivable from related parties	250,000,000		0
Amount outstanding on line of credit	250,000,000		0
Other HSBC affiliates [Member]
Related Party Transaction [Line Items]
Extended loans and lines of credit	4,000,000,000
Loans and leases receivable from related parties	78,000,000		39,000,000
Amount outstanding on line of credit	0		0
HSBC Affiliates [Member]
Related Party Transaction [Line Items]
Long-term debt	7,846,000,000		7,845,000,000
Loans and leases receivable from related parties	2,688,000,000		2,274,000,000
Derivative, notional amount	897,000,000,000		809,500,000,000
Fair value of derivative assets and liabilities	79,000,000		$ 108,000,000
Fixed Rate Note Maturing March 2021 [Member] \| HNAH [Member] \| Senior debt [Member]
Related Party Transaction [Line Items]
Long-term debt	1,500,000,000
Fixed Rate Note Maturing May 2021 [Member] \| HNAH [Member] \| Senior debt [Member]
Related Party Transaction [Line Items]
Long-term debt	2,000,000,000
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
Fixed Rate Note Maturing March 2026 [Member] \| HNAH [Member] \| Senior debt [Member]
Related Party Transaction [Line Items]
Long-term debt	$ 1,500,000,000

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

No definition available.

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- Definition

Loan and lease receivable revolving line of credit outstanding.

+ References

No definition available.

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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
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- Definition

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.

+ References

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-SubTopic 10
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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.

+ References

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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.

+ References

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Cash outflow to owners or shareholders, excluding ordinary dividends. Includes special dividends.

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-Name Accounting Standards Codification
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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.

+ References

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- Definition

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.

+ References

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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.

+ References

No definition available.

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