Stock Issued During Period, Shares, Warrants Exercised

No definition available.

Name:	open_StockIssuedDuringPeriodSharesWarrantsExercised
Namespace Prefix:	open_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Exercise price per share or per unit of warrants or rights outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=123467817&loc=d3e21475-112644

+ Details

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Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- 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.

+ Details

Name:	us-gaap_ClassOfWarrantOrRightLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

+ References

+ Details

Name:	us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of warrants or rights outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_ClassOfWarrantOrRightOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of expense (income) related to adjustment to fair value of warrant liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section 25
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=109262497&loc=d3e20148-110875

+ Details

Name:	us-gaap_FairValueAdjustmentOfWarrants
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash inflow associated with the amount received from holders exercising their stock warrants.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_ClassOfWarrantOrRightAxis=open_SeriesEWarrantsMember
Namespace Prefix:
Data Type:	na
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Period Type:

- Details

Name:	us-gaap_ClassOfWarrantOrRightAxis=open_PennyWarrantsWarrantCommitmentAndSeriesEWarrantsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

WARRANTS - Commitment to Issue Warrants (Details) - USD ($) $ / shares in Units, $ in Millions			12 Months Ended
	Jul. 09, 2021	Nov. 07, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Class of Warrant or Right [Line Items]
Warrants to purchase shares (in shares)			19,933,333
Exercise price of warrants (in dollars per share)			$ 11.50
Proceeds from warrant exercise	$ 22		$ 22	$ 0	$ 0
Increase to the warrant fair value adjustments			$ (12)	(31)	(6)
Series E Warrants
Class of Warrant or Right [Line Items]
Warrants to purchase shares (in shares)						242,713	121,356
Exercise price of warrants (in dollars per share)						$ 5.92	$ 5.92
Shares exercised and issued (in shares)		364,069
Proceeds from warrant exercise		$ 2
Warrants to purchase shares (in shares)			0
Penny Warrants, Warrant Commitment, and Series E Warrants
Class of Warrant or Right [Line Items]
Increase to the warrant fair value adjustments			$ 0	$ 3	$ 6