| Document and Entity Information | Apr. 28, 2020 |
| Document Type | 8-K |
| Document Period End Date | Apr. 28, 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, State or Province | MN |
| Entity Address, City or Town | Saint Paul |
| Entity Address, Postal Zip Code | 55102 |
| City Area Code | 800 |
| Local Phone Number | 232-6522 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000031462 |
| Amendment Flag | false |
| Common Stock [Member] | |
| Title of 12(b) Security | Common Stock, $1.00 par value |
| Trading Symbol | ECL |
| Security Exchange Name | NYSE |
| Euro Notes due 2025 [Member} | |
| Title of 12(b) Security | 2.625% Euro Notes due 2025 |
| Trading Symbol | ECL 25 |
| Security Exchange Name | NYSE |
| Euro Notes due 2024 [Member] | |
| Title of 12(b) Security | 1.000% Euro Notes due 2024 |
| Trading Symbol | ECL 24 |
| Security Exchange Name | NYSE |
