Consolidated Statements of Operations (unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenues	$ 418.7	$ 513.6	$ 840.2	$ 983.1
Cost of goods sold	299.4	304.2	561.3	585.1
Gross profit	119.3	209.4	278.9	398.0
Selling, general and administrative expenses	71.9	76.3	143.0	149.5
Research and development expenses	16.7	16.3	33.7	33.3
Costs related to legacy matters	2.8	1.5	5.5	48.4
Equity in earnings of unconsolidated affiliate	(3.4)	(6.0)	(4.6)	(10.1)
Restructuring and repositioning expenses	23.9	6.4	26.6	8.7
Interest expense and related financing costs	19.2	19.6	37.5	39.6
Other (income) expense, net	(8.6)	0.1	(17.4)	(2.1)
Total costs and expenses	122.5	114.2	224.3	267.3
Income (loss) before income taxes	(3.2)	95.2	54.6	130.7
(Provision for) benefit from income taxes	(6.4)	(18.8)	(22.1)	(29.7)
Net income (loss)	(9.6)	76.4	32.5	101.0
Less: Net (income) loss attributable to noncontrolling interests	2.3	(0.2)	2.2	(0.1)
Net income (loss) attributable to W. R. Grace & Co. shareholders	$ (7.3)	$ 76.2	$ 34.7	$ 100.9
Basic earnings per share:
Net income (loss) (in dollars per share)	$ (0.11)	$ 1.14	$ 0.52	$ 1.51
Weighted average number of basic shares (in shares)	66.2	66.8	66.3	66.8
Diluted earnings per share:
Net income (loss) (in dollars per shares)	$ (0.11)	$ 1.14	$ 0.52	$ 1.51
Weighted average number of diluted shares (in shares)	66.2	67.0	66.4	66.9
Dividends per common share (in dollars per shares)	$ 0.30	$ 0.27	$ 0.60	$ 0.54