Consolidated Statements of Comprehensive Loss (unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 1.6	$ 1.8
Other comprehensive loss:
Defined benefit pension and other postretirement plans, net of income taxes	0.0	0.1
Currency translation adjustments, net of income taxes	(8.0)	(33.8)
Gain from hedging activities, net of income taxes	0.0	0.2
Total other comprehensive loss	(8.0)	(33.5)
Comprehensive loss	(6.4)	(31.7)
Less: Comprehensive income attributable to noncontrolling interests	(0.1)	(0.1)
Comprehensive loss attributable to GCP shareholders	$ (6.5)	$ (31.8)