SPECIAL (GAINS) AND CHARGES - Restructuring Activities, Acquisition and Integration Related Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Restructuring
Restructuring liability	$ 75.8		$ 75.8
Cash payments			17.8
Acquisition, integrated and other related costs
Property, Plant and Equipment, Net	3,778.0		3,778.0		$ 3,707.1
Special (gains) and charges
Restructuring
Restructuring charges incurred, pre-tax	73.1	$ 4.1	82.3	$ 34.6
Acquisition, integrated and other related costs
Acquisition and integration costs	2.4	1.8	4.7	12.7
Acquisition and integration costs, after tax	1.6		3.3
Other special gains and charges	0.1	2.2	26.7	9.1
Other special gains and charges, after-tax	0.1		20.6
Other, Ecolab Foundation, pre-tax			25.0
Other, Ecolab Foundation, after tax			18.9
Foreign currency translation (charges) recovery associated with remeasurement and deconsolidation, before tax		3.2		8.5
Special (gains) and charges | Anios and Swisher
Acquisition, integrated and other related costs
Acquisition and integration costs		1.8		12.7
Acquisition and integration costs, after tax		1.2		8.5
Cost of sales
Restructuring
Restructuring charges incurred, pre-tax	5.9		6.3	2.2
Acquisition, integrated and other related costs
Acquisition and integration costs	(0.1)	0.3	(0.6)	12.9
Acquisition and integration costs, after tax		0.2		8.2
Other special gains and charges	(2.2)		(2.2)	11.1
Global Energy
Acquisition, integrated and other related costs
Contract termination and litigation related charges, before tax		2.2		20.2
Contract termination and litigation related charges, after tax		1.4		15.9
VENEZUELA
Acquisition, integrated and other related costs
Foreign currency translation (charges) recovery associated with remeasurement and deconsolidation, before tax		3.2		8.5
Foreign currency translation (charges) recovery associated with remeasurement and deconsolidation, after tax		2.0		5.3
Product and equipment
Acquisition, integrated and other related costs
Other special gains and charges	2.2
Other special gains and charges, after-tax	1.7
2018 Restructuring Plan
Restructuring
Restructuring charge expected to be incurred, pre-tax	170.0		170.0
Restructuring charge expected to be incurred, after tax	130.0		130.0
2018 Restructuring Plan | Special (gains) and charges
Restructuring
Restructuring charges incurred, pre-tax	79.4		89.5
Restructuring charges incurred, after tax	60.5		68.1
Restructuring liability	75.8		75.8
Prior Year Plans
Restructuring
Restructuring liability	22.5		22.5		$ 41.5
Prior Year Plans | Special (gains) and charges
Restructuring
Restructuring charges incurred, pre-tax		4.1		36.8
Restructuring charges incurred, after tax		$ 1.7		$ 25.9
Restructuring net gain	0.4		0.9
Restructuring net gain, net of tax	$ 0.3		$ 0.6