CONSOLIDATED STATEMENT OF INCOME - USD ($) shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net sales	$ 3,760.5	$ 3,747.2	$ 3,689.6	$ 3,470.9	$ 3,649.0	$ 3,564.5	$ 3,460.0	$ 3,162.4	$ 14,668.2	$ 13,835.9	$ 13,151.8
Cost of sales (including special charges of (a))	2,216.8	2,190.7	2,146.1	2,072.3	2,129.0	2,055.7	2,036.6	1,842.9	8,625.9	8,064.2	7,533.9
Selling, general and administrative expenses	948.8	964.7	1,036.8	1,018.3	962.4	939.8	967.0	956.1	3,968.6	3,825.3	3,708.2
Special (gains) and charges	13.0	75.6	12.1	26.0	(51.6)	4.9	36.8	6.2	126.7	(3.7)	39.5
Operating income	581.9	516.2	494.6	354.3	609.2	564.1	419.6	357.2	1,947.0	1,950.1	1,870.2
Other (income) expense	(19.9)	(21.0)	(19.6)	(19.4)	(16.8)	(16.9)	(16.8)	(16.8)	(79.9)	(67.3)	(43.8)
Interest expense, net	53.9	55.7	56.3	56.4	77.8	55.1	59.6	62.5	222.3	255.0	264.6
Income before income taxes	547.9	481.5	457.9	317.3	548.2	525.9	376.8	311.5	1,804.6	1,762.4	1,649.4
Provision for income taxes	147.7	43.2	104.3	69.1	(20.2)	129.3	80.5	54.2	364.3	243.8	402.9
Net income including noncontrolling interest	400.2	438.3	353.6	248.2	568.4	396.6	296.3	257.3	1,440.3	1,518.6	1,246.5
Net income attributable to noncontrolling interest	5.1	2.9	2.3	0.9	5.8	3.4	1.5	3.3	11.2	14.0	17.5
Net income attributable to Ecolab	$ 395.1	$ 435.4	$ 351.3	$ 247.3	$ 562.6	$ 393.2	$ 294.8	$ 254.0	$ 1,429.1	$ 1,504.6	$ 1,229.0
Earnings attributable to Ecolab per common share
Basic (in dollars per share)	$ 1.37	$ 1.51	$ 1.22	$ 0.86	$ 1.95	$ 1.36	$ 1.02	$ 0.87	$ 4.95	$ 5.20	$ 4.20
Diluted (in dollars per share)	$ 1.35	$ 1.48	$ 1.20	$ 0.84	$ 1.92	$ 1.34	$ 1.00	$ 0.86	$ 4.88	$ 5.12	$ 4.14
Weighted-average common shares outstanding
Basic (in shares)	288.0	288.8	288.8	288.6	289.1	289.0	289.8	290.6	288.6	289.6	292.5
Diluted (in shares)	292.2	293.4	293.3	292.7	293.6	293.4	294.1	295.0	292.8	294.0	296.7
Product and sold equipment
Net sales									$ 12,128.6	$ 11,431.8	$ 10,904.1
Cost of sales (including special charges of (a))									7,078.5	6,576.9	6,153.3
Service and lease equipment
Net sales									2,539.6	2,404.1	2,247.7
Cost of sales (including special charges of (a))									$ 1,547.4	$ 1,487.3	$ 1,380.6