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Investments in affiliates and joint ventures - Narrative (Details)	12 Months Ended
	Dec. 31, 2019	Nov. 01, 2018
Nuna East Ltd.
Variable Interest Entity [Line Items]
Ownership percentage	37.25%	37.25%
Nuna West Mining Ltd.
Variable Interest Entity [Line Items]
Ownership percentage	49.00%	49.00%
Nuna Pang Contracting Ltd.
Variable Interest Entity [Line Items]
Ownership percentage	37.25%	37.25%
Nuna Logistics Partnership
Variable Interest Entity [Line Items]
Ownership percentage	49.00%	49.00%
Dene North Site Services Partnership | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
NL Partnership Interest in VIEs	49.00%
Mikisew North American Limited Partnership [Member] | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
NL Partnership Interest in VIEs	49.00%

X

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

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+ References

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- Definition

Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=118582676&loc=SL6759159-111685

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