ACCUMULATED OTHER COMPREHENSIVE EARNINGS (LOSSES) (AOCE) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 2,093	$ 1,828	$ 1,905
Net current period activity	20	(48)	142
Ending balance	2,060	2,093	1,828
Foreign Currency Translation and Other
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(264)	(223)	(316)
Other comprehensive earnings (loss) before reclassifications, net of tax	25	(43)	75
Amounts reclassified to Net earnings	1	2	18
Amounts reclassified to Retained earnings		0
Net current period activity	26	(41)	93
Ending balance	(238)	(264)	(223)
AOCI Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(187)	(154)	(296)
Other comprehensive earnings (loss) before reclassifications, net of tax	30	(40)	162
Amounts reclassified to Net earnings	(10)	(8)	(20)
Amounts reclassified to Retained earnings		15
Net current period activity	20	(33)	142
Ending balance	(167)	(187)	(154)
AOCI Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(16)	(19)	(23)
Ending balance	(13)	(16)	(19)
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	3	4
Amounts reclassified to Net earnings	0	0	0
Amounts reclassified to Retained earnings		0
Net current period activity	3	3	4
AOCE Attributable to W.W. Grainger, Inc.
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(171)	(135)	(273)
Net current period activity	17	(51)	138
Ending balance	(154)	(171)	(135)
AOCE Attributable to W.W. Grainger, Inc.
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(171)	(135)	(273)
Other comprehensive earnings (loss) before reclassifications, net of tax	27	(43)	158
Amounts reclassified to Net earnings	(10)	(8)	(20)
Amounts reclassified to Retained earnings		15
Net current period activity	17	(36)	138
Ending balance	(154)	(171)	(135)
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	82	73	25
Other comprehensive earnings (loss) before reclassifications, net of tax	8	4	86
Amounts reclassified to Net earnings	(11)	(10)	(38)
Amounts reclassified to Retained earnings		15
Net current period activity	(3)	9	48
Ending balance	79	82	73
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	(5)	(4)	(5)
Other comprehensive earnings (loss) before reclassifications, net of tax	(3)	(1)	1
Amounts reclassified to Net earnings	0	0	0
Amounts reclassified to Retained earnings		0
Net current period activity	(3)	(1)	1
Ending balance	$ (8)	$ (5)	$ (4)

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