CONDENSED CONSOLIDATED STATEMENTS OF EARNINGS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Net sales	$ 2,615,269	$ 2,563,668	$ 5,156,398	$ 5,070,206
Cost of merchandise sold	1,575,313	1,523,609	3,097,250	2,985,094
Gross profit	1,039,956	1,040,059	2,059,148	2,085,112
Warehousing, marketing and administrative expenses	807,891	734,470	1,531,595	1,462,431
Operating earnings	232,065	305,589	527,553	622,681
Other income (expense):
Interest income	465	162	658	327
Interest expense	(19,905)	(16,806)	(36,884)	(30,531)
Loss from equity method investment	(6,121)	(5,427)	(14,495)	(11,815)
Other non-operating income and (expense)	692	(538)	1,037	(98)
Total other expense	(24,869)	(22,609)	(49,684)	(42,117)
Earnings before income taxes	207,196	282,980	477,869	580,564
Income taxes	100,237	103,535	188,057	209,475
Net earnings	106,959	179,445	289,812	371,089
Less: Net earnings attributable to noncontrolling interest	9,038	6,769	17,147	11,700
Net earnings attributable to W.W. Grainger, Inc.	$ 97,921	$ 172,676	$ 272,665	$ 359,389
Earnings per share:
Basic (in dollars per share)	$ 1.68	$ 2.81	$ 4.64	$ 5.81
Diluted (in dollars per share)	$ 1.67	$ 2.79	$ 4.61	$ 5.77
Weighted average number of shares outstanding:
Basic (in shares)	58,012,731	60,891,298	58,363,416	61,278,981
Diluted (in shares)	58,287,312	61,301,545	58,741,262	61,699,603
Cash dividends paid per share (in dollars per share)	$ 1.28	$ 1.22	$ 2.50	$ 2.39