CONSOLIDATED STATEMENT OF INCOME - USD ($) shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CONSOLIDATED STATEMENT OF INCOME
Net sales	$ 3,650.7	$ 3,563.3	$ 3,462.7	$ 3,161.6	$ 3,352.1	$ 3,386.1	$ 3,317.2	$ 3,097.4	$ 13,838.3	$ 13,152.8	$ 13,545.1
Cost of sales (including special charges of (a))	1,950.7	1,891.3	1,871.6	1,691.5	1,745.1	1,737.2	1,785.2	1,631.4	7,405.1	6,898.9	7,223.5
Selling, general and administrative expenses	1,123.9	1,087.3	1,115.3	1,090.6	1,046.3	1,071.6	1,093.3	1,088.2	4,417.1	4,299.4	4,345.5
Special (gains) and charges	(51.6)	4.9	36.8	6.2	3.8	3.2	26.2	6.3	(3.7)	39.5	414.8
Operating income	627.7	579.8	439.0	373.3	556.9	574.1	412.5	371.5	2,019.8	1,915.0	1,561.3
Interest expense, net	77.8	55.1	59.6	62.5	68.3	64.9	65.3	66.1	255.0	264.6	243.6
Income before income taxes	549.9	524.7	379.4	310.8	488.6	509.2	347.2	305.4	1,764.8	1,650.4	1,317.7
Provision for income taxes	(21.8)	128.9	81.3	54.0	116.6	129.7	83.6	73.4	242.4	403.3	300.5
Net income including noncontrolling interest	571.7	395.8	298.1	256.8	372.0	379.5	263.6	232.0	1,522.4	1,247.1	1,017.2
Net income attributable to noncontrolling interest	5.8	3.4	1.5	3.3	5.7	5.4	5.2	1.2	14.0	17.5	15.1
Net income attributable to Ecolab	$ 565.9	$ 392.4	$ 296.6	$ 253.5	$ 366.3	$ 374.1	$ 258.4	$ 230.8	$ 1,508.4	$ 1,229.6	$ 1,002.1
Earnings attributable to Ecolab per common share
Basic (in dollars per share)	$ 1.96	$ 1.36	$ 1.02	$ 0.87	$ 1.26	$ 1.28	$ 0.88	$ 0.78	$ 5.21	$ 4.20	$ 3.38
Diluted (in dollars per share)	$ 1.93	$ 1.34	$ 1.01	$ 0.86	$ 1.24	$ 1.27	$ 0.87	$ 0.77	5.13	4.14	3.32
Dividends declared per common share (in dollars per share)									$ 1.520	$ 1.420	$ 1.340
Weighted-average common shares outstanding
Basic (in shares)	289.1	289.0	289.8	290.6	291.7	291.6	292.4	294.4	289.6	292.5	296.4
Diluted (in shares)	293.6	293.4	294.1	295.0	295.5	295.7	296.5	298.3	294.0	296.7	301.4