Consolidated Statements of Comprehensive (Loss) Income (unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 43.5	$ 38.5	$ 86.4	$ 38.8
Other comprehensive income (loss):
Defined benefit pension and other postretirement plans, net of income taxes	(0.4)	(0.4)	(0.7)	(0.7)
Currency translation adjustments	(8.3)	1.3	(9.7)	(4.1)
Gain (loss) from hedging activities, net of income taxes	(0.2)	(0.3)	0.5	(3.3)
Total other comprehensive income (loss) attributable to noncontrolling interests		0.0	0.0	2.6
Total other comprehensive income (loss)	(8.9)	0.6	(9.9)	(5.5)
Comprehensive income (loss)	34.6	39.1	76.5	33.3
Less: comprehensive (income) loss attributable to noncontrolling interests	0.4	0.2	0.4	(2.2)
Comprehensive income (loss) attributable to W. R. Grace & Co. shareholders	$ 35.0	$ 39.3	$ 76.9	$ 31.1