ACCUMULATED OTHER COMPREHENSIVE EARNINGS (LOSSES) (AOCE) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 1,828
Net current period activity	(48)	$ 142	$ (51)
Ending balance	2,093	1,828
Foreign Currency Translation and Other
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(223)	(316)	(277)
Other comprehensive earnings (loss) before reclassifications, net of tax	(43)	75	(39)
Amounts reclassified to Net earnings	2	18	0
Amounts reclassified to Retained earnings	0
Net current period activity	(41)	93	(39)
Ending balance	(264)	(223)	(316)
AOCI Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(154)	(296)	(245)
Other comprehensive earnings (loss) before reclassifications, net of tax	(40)	162	(47)
Amounts reclassified to Net earnings	(8)	(20)	(4)
Amounts reclassified to Retained earnings	15
Net current period activity	(33)	142	(51)
Ending balance	(187)	(154)	(296)
AOCI Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(19)	(23)	(24)
Ending balance	(16)	(19)	(23)
Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive earnings (loss) before reclassifications, net of tax	3	4	1
Amounts reclassified to Net earnings	0	0	0
Amounts reclassified to Retained earnings	0
Net current period activity	3	4	1
AOCE Attributable to W.W. Grainger, Inc.
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(135)	(273)	(221)
Net current period activity	(51)	138	(52)
Ending balance	(171)	(135)	(273)
AOCE Attributable to W.W. Grainger, Inc.
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(135)	(273)	(221)
Other comprehensive earnings (loss) before reclassifications, net of tax	(43)	158	(48)
Amounts reclassified to Net earnings	(8)	(20)	(4)
Amounts reclassified to Retained earnings	15
Net current period activity	(36)	138	(52)
Ending balance	(171)	(135)	(273)
Defined Postretirement Benefit Plan \| Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	73	25	35
Other comprehensive earnings (loss) before reclassifications, net of tax	4	86	(6)
Amounts reclassified to Net earnings	(10)	(38)	(4)
Amounts reclassified to Retained earnings	15
Net current period activity	9	48	(10)
Ending balance	82	73	25
Other Employment-related Benefit Plans \| Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(4)	(5)	(3)
Other comprehensive earnings (loss) before reclassifications, net of tax	(1)	1	(2)
Amounts reclassified to Net earnings	0	0	0
Amounts reclassified to Retained earnings	0
Net current period activity	(1)	1	(2)
Ending balance	$ (5)	$ (4)	$ (5)

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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