EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share [Abstract]
Net earnings attributable to W.W. Grainger, Inc. as reported	$ 205,915	$ 217,660	$ 422,568	$ 429,498
Distributed earnings available to participating securities	(727)	(826)	(1,562)	(1,717)
Undistributed earnings available to participating securities	(1,666)	(2,265)	(3,765)	(5,006)
Numerator for basic earnings per share – Undistributed and distributed earnings available to common shareholders	203,522	214,569	417,241	422,775
Undistributed earnings allocated to participating securities	1,666	2,265	3,765	5,006
Undistributed earnings reallocated to participating securities	(1,645)	(2,230)	(3,716)	(4,925)
Numerator for diluted earnings per share – Undistributed and distributed earnings available to common shareholders	$ 203,543	$ 214,604	$ 417,290	$ 422,856
Denominator for basic earnings per share - weighted average shares (in shares)	68,453,602	69,664,697	68,576,232	69,613,947
Effect of dilutive securities	888,283	1,136,353	932,893	1,174,256
Denominator for diluted earnings per share - weighted average shares adjusted for dilutive securities (in shares)	69,341,885	70,801,050	69,509,125	70,788,203
Basic (in dollars per share)	$ 2.97	$ 3.08	$ 6.08	$ 6.07
Diluted (in dollars per share)	$ 2.94	$ 3.03	$ 6.00	$ 5.97