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Income Taxes - Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2015
Income Tax Disclosure [Abstract] |  |
Unrecognized tax benefit beginning balance | $ 1 |
Gross increases - tax positions in current period |  | $ 1
Settlement | (1) |
Unrecognized tax benefit ending balance | $ 0 | $ 1

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- Definition Unrecognized tax benefits gross increases resulting from current period tax positions. + References No definition available. + Details
Name: | dnow_UnrecognizedTaxBenefitsGrossIncreasesResultingFromCurrentPeriodTaxPositions
Namespace Prefix: | dnow_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Unrecognized tax benefits increases or (decreases) related to settlements. + References No definition available. + Details
Name: | dnow_UnrecognizedTaxBenefitsIncreasesOrDecreasesRelatedToSettlements
Namespace Prefix: | dnow_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_IncomeTaxDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
Name: | us-gaap_UnrecognizedTaxBenefits
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant