Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Jan. 29, 2021	Jun. 30, 2020
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2020
Entity File Number	1-9328
Entity Registrant Name	ECOLAB INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	41-0231510
Entity Address, Address Line One	1 Ecolab Place
Entity Address, City or Town	St. Paul
Entity Address, State or Province	MN
Entity Address, Postal Zip Code	55102
City Area Code	800
Local Phone Number	232-6522
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 56,528,667,907
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		285,849,956
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0000031462
Amendment Flag	false
Common Stock
Title of 12(b) Security	Common Stock, $1.00 par value
Trading Symbol	ECL
Security Exchange Name	NYSE
2.625% Euro Notes due 2025
Title of 12(b) Security	2.625% Euro Notes due 2025
Trading Symbol	ECL 25
Security Exchange Name	NYSE
1.000% Euro Notes due 2024
Title of 12(b) Security	1.000% Euro Notes due 2024
Trading Symbol	ECL 24
Security Exchange Name	NYSE