Consolidated Statements of Operations (unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenues	$ 419.4	$ 470.5	$ 1,259.6	$ 1,453.6
Cost of goods sold	263.0	279.5	824.3	864.6
Gross profit	156.4	191.0	435.3	589.0
Selling, general and administrative expenses	68.1	74.2	211.1	223.7
Research and development expenses	15.6	14.9	49.3	48.2
Costs related to legacy matters	30.6	3.7	36.1	52.1
Equity in earnings of unconsolidated affiliate	(1.3)	(3.8)	(5.9)	(13.9)
Restructuring and repositioning expenses	2.4	3.4	29.0	12.1
Gain (Loss) on Extinguishment of Debt	(39.4)	0.0	(39.4)	0.0
Interest and Debt Expense Excluding Loss on Debt Extinguishment	19.8	18.6	57.3	58.2
Other (income) expense, net	5.3	(1.1)	(12.1)	(3.2)
Total costs and expenses	179.9	109.9	404.2	377.2
Income (loss) before income taxes	(23.5)	81.1	31.1	211.8
(Provision for) benefit from income taxes	30.2	(27.3)	8.1	(57.0)
Net income (loss)	6.7	53.8	39.2	154.8
Less: Net (income) loss attributable to noncontrolling interests	0.3	(0.1)	2.5	(0.2)
Net income (loss) attributable to W. R. Grace & Co. shareholders	$ 7.0	$ 53.7	$ 41.7	$ 154.6
Basic earnings per share:
Net income (loss) (in dollars per share)	$ 0.11	$ 0.81	$ 0.63	$ 2.31
Weighted average number of basic shares (in shares)	66.2	66.7	66.3	66.8
Diluted earnings per share:
Net income (loss) (in dollars per shares)	$ 0.11	$ 0.80	$ 0.63	$ 2.31
Weighted average number of diluted shares (in shares)	66.2	66.8	66.3	66.9
Dividends per common share (in dollars per shares)	$ 0.30	$ 0.27	$ 0.90	$ 0.81