EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Notes Details [Abstract]
Net earnings attributable to W.W. Grainger, Inc. as reported	$ 217,660	$ 190,704	$ 429,498	$ 378,220
Distributed earnings available to participating securities	(826)	(996)	(1,717)	(1,706)
Undistributed earnings available to participating securities	(2,265)	(2,503)	(5,006)	(5,143)
Numerator for basic earnings per share - Undistributed and distributed earnings available to common shareholders	214,569	187,205	422,775	371,371
Undistributed earnings allocated to participating securities	2,265	2,503	5,006	5,143
Undistributed earnings reallocated to participating securities	(2,230)	(2,455)	(4,925)	(5,041)
Numerator for diluted earnings per share - Undistributed and distributed earnings available to common shareholders	$ 214,604	$ 187,253	$ 422,856	$ 371,473
Denominator for basic earnings per share - weighted average shares (in shares)	69,664,697	69,937,085	69,613,947	70,034,142
Effect of dilutive securities (in shares)	1,136,353	1,370,555	1,174,256	1,446,535
Denominator for diluted earnings per share - weighted average shares adjusted for dilutive securities (in shares)	70,801,050	71,307,640	70,788,203	71,480,677
Earnings per share Two-class method
Basic (in dollars per share)	$ 3.08	$ 2.68	$ 6.07	$ 5.30
Diluted (in dollars per share)	$ 3.03	$ 2.63	$ 5.97	$ 5.20