CONDENSED CONSOLIDATED STATEMENTS OF EARNINGS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Net sales	$ 2,541,129	$ 2,506,538
Cost of merchandise sold	1,521,937	1,461,485
Gross profit	1,019,192	1,045,053
Warehousing, marketing and administrative expenses	723,704	727,961
Operating earnings	295,488	317,092
Other income (expense):
Interest income	193	165
Interest expense	(16,979)	(13,725)
Loss from equity method investment	(8,374)	(6,388)
Other non-operating income	345	440
Total other expense, net	(24,815)	(19,508)
Earnings before income taxes	270,673	297,584
Income taxes	87,820	105,940
Net earnings	182,853	191,644
Less: Net earnings attributable to noncontrolling interest	8,109	4,931
Net earnings attributable to W.W. Grainger, Inc.	$ 174,744	$ 186,713
Earnings per share:
Basic (in dollars per share)	$ 2.95	$ 3.00
Diluted (in dollars per share)	$ 2.93	$ 2.98
Weighted average number of shares outstanding:
Basic (in shares)	58,720,066	61,668,682
Diluted (in shares)	59,202,882	62,099,801
Cash dividends paid per share (in dollars per share)	$ 1.22	$ 1.17