Provisions - Summary of Provisions (Detail) - CAD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure of Provisions [line items]
Decommissioning liability	$ 60	$ 100	$ 129
Office lease provision	35	13	$ 22
Total	95	113
Current portion	17	16
Long-term portion	$ 78	$ 97

The amount of current provisions. [Refer: Provisions]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-IssueDate 2020-01-01
-Paragraph 54
-Subparagraph l
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-URIDate 2020-01-01

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of non-current provisions. [Refer: Provisions]

+ References

+ Details

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of provision for costs related to decommissioning, restoration and rehabilitation. [Refer: Other provisions]

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 37
-IssueDate 2020-01-01
-Section D Examples: disclosures
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=37&code=ifrs-tx-2020-en-r&doctype=Illustrative%20Examples&dita_xref=IAS37_IE_D_TI
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-URIDate 2020-01-01

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Balance Type:	credit
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- Definition

The amount of liabilities of uncertain timing or amount.

+ References

+ Details

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Namespace Prefix:	ifrs-full_
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Balance Type:	credit
Period Type:	instant

- Definition

Disclosure of provisions line items.

+ References

No definition available.

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Namespace Prefix:	obe_
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Balance Type:	na
Period Type:	duration

- Definition

Office lease provision.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant