Consolidated Statements of Comprehensive (Loss) Income (unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 47.1	$ 39.7	$ 133.5	$ 78.5
Other comprehensive income (loss):
Defined benefit pension and other postretirement plans, net of income taxes	(0.3)	(0.3)	(1.0)	(1.0)
Currency translation adjustments, net of income taxes	(12.1)	(2.3)	(21.8)	(6.4)
Gain (loss) from hedging activities, net of income taxes	(0.4)	0.6	0.1	(2.7)
Total other comprehensive income (loss) attributable to noncontrolling interests	0.0	0.0	0.0	2.6
Total other comprehensive income (loss)	(12.8)	(2.0)	(22.7)	(7.5)
Comprehensive income (loss)	34.3	37.7	110.8	71.0
Less: comprehensive (income) loss attributable to noncontrolling interests	0.3	(0.1)	0.7	(2.3)
Comprehensive income (loss) attributable to W. R. Grace & Co. shareholders	$ 34.6	$ 37.6	$ 111.5	$ 68.7