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SEGMENT INFORMATION - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) segment
Segment Reporting Information [Line Items]
Number of reportable segments | segment			2
Service revenues, percent of total revenues			1.00%
Unallocated expenses increase	$ 45	$ 37
Write down of corporate aircraft	$ 9
Unallocated expenses increase, percent	22.00%
United States [Member]
Segment Reporting Information [Line Items]
Intersegment sales increase	$ 17		$ 36

X

- Definition

Increase in Intersegment Sales for the respective Reporting Segment.

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	duration

X

- Definition

Grainger's Service Fee Revenue as a percentage of sales.

+ References

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Namespace Prefix:	gww_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Unallocated Expenses Increase (Decrease), Amount

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- Definition

Unallocated Expenses Increase (Decrease), Percent

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X

- Definition

The aggregate amount of write-downs for impairments recognized during the period for long-lived assets held for abandonment, exchange or sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2611-110228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

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X

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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