Consolidated Statements of Operations (unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenues	$ 470.5	$ 494.9	$ 1,453.6	$ 1,412.1
Cost of goods sold	279.5	292.7	864.6	841.7
Gross profit	191.0	202.2	589.0	570.4
Selling, general and administrative expenses	74.2	74.7	223.7	223.5
Research and development expenses	14.9	15.7	48.2	46.5
Costs related to legacy matters	3.7	74.6	52.1	78.8
Equity in earnings of unconsolidated affiliate	(3.8)	(5.9)	(13.9)	(19.5)
Restructuring and repositioning expenses	3.4	8.4	12.1	32.8
Interest expense and related financing costs	18.6	20.4	58.2	59.6
Other (income) expense, net	(1.1)	(2.3)	(3.2)	0.3
Total costs and expenses	109.9	185.6	377.2	422.0
Income (loss) before income taxes	81.1	16.6	211.8	148.4
(Provision for) benefit from income taxes	(27.3)	(0.7)	(57.0)	(50.5)
Net income (loss)	53.8	15.9	154.8	97.9
Less: Net (income) loss attributable to noncontrolling interests	(0.1)	0.2	(0.2)	0.6
Net income (loss) attributable to W. R. Grace & Co. shareholders	$ 53.7	$ 16.1	$ 154.6	$ 98.5
Basic earnings per share:
Net income (loss) (in dollars per share)	$ 0.81	$ 0.24	$ 2.31	$ 1.46
Weighted average number of basic shares (in shares)	66.7	67.1	66.8	67.3
Diluted earnings per share:
Net income (loss) (in dollars per shares)	$ 0.80	$ 0.24	$ 2.31	$ 1.46
Weighted average number of diluted shares (in shares)	66.8	67.2	66.9	67.4
Dividends per common share (in dollars per shares)	$ 0.27	$ 0.24	$ 0.81	$ 0.72