Consolidated Statements of Comprehensive (Loss) Income (unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 1.2	$ 21.6
Other comprehensive (loss) income:
Defined benefit pension and other postretirement plans, net of income taxes	0.1	0.0
Currency translation adjustments, net of income taxes	(33.8)	3.3
Gain (loss) from hedging activities, net of income taxes	0.2	(0.1)
Total other comprehensive (loss) income	(33.5)	3.2
Comprehensive (loss) income	(32.3)	24.8
Less: Comprehensive income attributable to noncontrolling interests	(0.1)	(0.2)
Comprehensive (loss) income attributable to GCP shareholders	$ (32.4)	$ 24.6