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INVENTORIES - Activity in reserves for excess and obsolete inventory (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Inventory Disclosure [Abstract] |  |
Balance at beginning of period | $ (193) | $ (191)
Provision for excess and obsolete inventory | (20) | (25)
Disposal of unsaleable inventory | 55 | 29
Other | 4 | (6)
Balance at end of period | $ (154) | $ (193)

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- Definition Inventory Valuation Reserve, Adjustments for Business Acquisitions, Foreign Currency and Other + References No definition available. + Details
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- Definition Inventory Valuation Reserve, Disposal of Unsaleable Inventory + References No definition available. + Details
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Namespace Prefix: | gww_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Inventory Valuation Reserve, Provision for Excess and Obsolete Inventory + References No definition available. + Details
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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
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- Definition Amount of valuation reserve for inventory. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 330 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.BB) -URI http://asc.fasb.org/extlink&oid=27011343&loc=d3e100047-122729 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.6(a)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 330 -SubTopic 10 -Section 35 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=68049868&loc=d3e3927-108312 + Details
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Period Type: | instant