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Investments in affiliates and joint ventures - Ownership Percentages (Details)	12 Months Ended
	Dec. 31, 2018
Kivalliq Services Ltd.
Variable Interest Entity [Line Items]
NL Partnership Interest in equity method investments	33.33%
HRN Contracting Ltd.
Variable Interest Entity [Line Items]
NL Partnership Interest in equity method investments	33.33%
Amik Nuna Forestry Services | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
NL Partnership Interest in VIEs	50.00%
Aroland Nuna | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
NL Partnership Interest in VIEs	49.00%
Fond Du Lac Nuna | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
NL Partnership Interest in VIEs	49.00%
Mahiikanuk Nuna | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
NL Partnership Interest in VIEs	49.00%
Met Nuna | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
NL Partnership Interest in VIEs	75.00%
Nuna Bauer | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
NL Partnership Interest in VIEs	50.00%
EDC Nuna Contracting | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
NL Partnership Interest in VIEs	70.00%
Attawapiskat Nuna | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
NL Partnership Interest in VIEs	75.00%
Westarc Drilling & Blasting Services Ltd. | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
NL Partnership Interest in VIEs	30.00%
Deton Cho Nuna | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
NL Partnership Interest in VIEs	60.00%
Nuna Deton Cho Winter Road Services | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
NL Partnership Interest in VIEs	75.00%
Nuna Deton Cho Contracting | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
NL Partnership Interest in VIEs	100.00%

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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- Definition

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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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 5A
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