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Basis of Presentation - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Maturity period of investments description	Three months or less

X

- Definition

Maturity period to qualify as cash equivalent maximum.

+ References

No definition available.

+ Details

Name:	nov_MaturityPeriodToQualifyAsCashEquivalentMaximum
Namespace Prefix:	nov_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

Name:	us-gaap_AccountingPoliciesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration