Consolidated Statements of Comprehensive Income (Loss) (unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 24.6	$ 43.4
Other comprehensive income (loss), net of income taxes:
Defined benefit pension and other postretirement plans	(0.1)	(0.2)
Currency translation adjustments	11.7	(18.2)
Gain (loss) from hedging activities	(3.0)	1.8
Total other comprehensive income (loss)	8.6	(16.6)
Comprehensive income (loss)	33.2	26.8
Less: comprehensive (income) loss attributable to noncontrolling interests	0.1	0.2
Comprehensive income (loss) attributable to W. R. Grace & Co. shareholders	$ 33.3	$ 27.0