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Cover
May 01, 2020
Cover [Abstract]  
Document Type 8-K
Document Period End Date May 01, 2020
Entity File Number 1-5684
Entity Registrant Name W.W. Grainger, Inc.
Entity Incorporation, State or Country Code IL
Entity Tax Identification Number 36-1150280
Entity Address, Address Line One 100 Grainger Parkway,
Entity Address, City or Town Lake Forest,
Entity Address, State or Province IL
Entity Address, Postal Zip Code 60045-5201
City Area Code 847
Local Phone Number   535-1000
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Title of 12(b) Security Common Stock
Trading Symbol GWW
Security Exchange Name NYSE
Entity Emerging Growth Company false
Entity Central Index Key 0000277135
Amendment Flag false