Consolidated Statements of Comprehensive Income (Loss) (unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 16.7	$ 25.5	$ 40.9	$ (8.8)
Other comprehensive loss:
Defined benefit pension and other postretirement plans, net of income taxes	0.0	0.2	0.0	(0.4)
Currency translation adjustments, net of income taxes	(14.9)	(9.1)	(15.5)	(27.3)
Gain from hedging activities, net of income taxes	0.1	0.0	0.0	0.1
Total other comprehensive loss	(14.8)	(8.9)	(15.5)	(27.6)
Comprehensive income (loss)	1.9	16.6	25.4	(36.4)
Less: Comprehensive income attributable to noncontrolling interests	(0.1)	(0.1)	(0.3)	(0.3)
Comprehensive income (loss) attributable to GCP shareholders	$ 1.8	$ 16.5	$ 25.1	$ (36.7)