SPECIAL (GAINS) AND CHARGES - Restructuring and Non-Restructuring Activity (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Restructuring
Recorded expense			$ 78.0		$ 104.6
Net cash payments			(50.3)		(35.2)
Non-cash charges			(0.8)		(5.0)
Effect of foreign currency translation			(0.2)		(0.5)
Restructuring liability	$ 90.6		90.6		63.9
Other restructuring information
Special (gains) and charges	49.9	$ 12.1	90.2	$ 38.1
Non-restructuring Special (Gains) and Charges
Property, Plant and Equipment, Net	3,866.9		3,866.9		3,836.0
Special (gains) and charges
Other restructuring information
Restructuring charges incurred, pre-tax	30.9	8.9	68.0	9.2
Upstream energy spin-off	14.5		18.8
Upstream energy spin-off, net of tax	12.4		15.7
Special (gains) and charges	49.9	12.1	90.2	38.1
Business combination advisory and legal fees, pre tax	0.4	1.8	2.9	2.3
Business combination advisory and legal fees, after tax	0.3	1.3	2.1	1.7
Other special gains and charges	4.1	1.4	0.5	26.6
Other special gains and charges, after-tax	3.1		(1.2)
Other, Ecolab Foundation, pre-tax				25.0
Other, Ecolab Foundation, after tax				18.9
Cost of sales
Other restructuring information
Restructuring charges incurred, pre-tax	6.6	0.4	10.0	0.4
Special (gains) and charges	7.9	(0.1)	11.5	(0.1)
Business combination advisory and legal fees, pre tax	1.3	(0.5)	1.5	(0.5)
Interest expense
Other restructuring information
Special (gains) and charges			0.2
Business combination advisory and legal fees, pre tax			0.2
Business combination advisory and legal fees, after tax			0.1
Employee termination costs
Restructuring
Recorded expense			63.6		94.1
Net cash payments			(39.8)		(32.8)
Effect of foreign currency translation			(0.2)		(0.5)
Restructuring liability	84.4		84.4		60.8
Asset disposals
Restructuring
Recorded expense			0.6		5.0
Net cash payments			0.2
Non-cash charges			(0.8)		(5.0)
Other
Restructuring
Recorded expense			13.8		5.5
Net cash payments			(10.7)		(2.4)
Restructuring liability	6.2		6.2		3.1
Product and sold equipment
Other restructuring information
Business combination advisory and legal fees, pre tax		0.5
Business combination advisory and legal fees, after tax		0.4
Product and sold equipment | Cost of sales
Other restructuring information
Special (gains) and charges	7.9	(0.1)	11.5	(0.1)
Business combination advisory and legal fees, pre tax			1.5
Business combination advisory and legal fees, after tax			1.1
2018 Restructuring Plan
Other restructuring information
Restructuring charge expected to be incurred, pre-tax	260.0		260.0
Restructuring charge expected to be incurred, after tax	190.0		190.0
2018 Restructuring Plan | Special (gains) and charges
Restructuring
Restructuring liability	90.6		90.6
Other restructuring information
Restructuring charges incurred to date, pre-tax	182.6		182.6
Restructuring charges incurred to date, after-tax	139.1		139.1
Restructuring charges incurred, pre-tax	37.5		78.0
Restructuring charges incurred, after tax	29.1		59.5
Prior Year Plans
Restructuring
Cash payments			(4.3)
Restructuring liability	$ 10.5		10.5		$ 14.9
Other restructuring information
Restructuring charges incurred, pre-tax		0.8		0.5
Restructuring charges incurred, after tax		$ 0.6		$ 0.3
Cash payments			$ 4.3