Consolidated Statements of Operations (unaudited) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019		Jun. 30, 2020		Jun. 30, 2019
Income Statement [Abstract]
Net sales		$ 195.4	$ 262.2		$ 412.1		$ 488.3
Cost of goods sold		119.0	163.2		253.8		307.1
Gross profit		76.4	99.0		158.3		181.2
Selling, general and administrative expenses		65.7	71.4		133.8		140.4
Research and development expenses		3.7	4.6		8.6		9.3
Interest expense and related financing costs		5.0	5.7		10.7		11.6
Repositioning expenses		1.0	5.8		3.7		11.2
Restructuring expenses and asset impairments		0.4	4.4		3.5		5.0
Other income, net		(2.7)	(1.7)		(4.9)		(3.5)
Total costs and expenses		73.1	90.2		155.4		174.0
Income from continuing operations before income taxes		3.3	8.8		2.9		7.2
(Provision for) benefit from income taxes		(4.5)	(5.7)		(2.6)		10.7
(Loss) income from continuing operations		(1.2)	3.1		0.3		17.9
(Loss) income from discontinued operations, net of income taxes		0.0	(0.5)		(0.3)		6.3
Net (loss) income		(1.2)	2.6		0.0		24.2
Less: Net income attributable to noncontrolling interests		(0.1)	0.0		(0.2)		(0.2)
Net (loss) income attributable to GCP shareholders		(1.3)	2.6		(0.2)		24.0
Amounts Attributable to GCP Shareholders:
(Loss) income from continuing operations attributable to GCP shareholders		(1.3)	3.1		0.1		17.7
(Loss) income from discontinued operations, net of income taxes		0.0	(0.5)		(0.3)		6.3
Net (loss) income attributable to GCP shareholders		$ (1.3)	$ 2.6		$ (0.2)		$ 24.0
Basic earnings (loss) per share:
(Loss) income from continuing operations attributable to GCP shareholders (in usd per share)	[1]	$ (0.02)	$ 0.04		$ 0		$ 0.24
(Loss) income from discontinued operations, net of income taxes (in usd per share)	[1]	0	(0.01)		0		0.09
Net (loss) income attributable to GCP shareholders (in usd per share)	[1],[2]	$ (0.02)	$ 0.04		$ 0		$ 0.33
Weighted average number of basic shares (in shares)	[1]	72,900,000	72,600,000		72,900,000		72,500,000
Diluted earnings (loss) per share:
(Loss) income from continuing operations attributable to GCP shareholders (in dollars per share)	[1]	$ (0.02)	$ 0.04		$ 0		$ 0.24
(Loss) income from discontinued operations, net of income taxes (in dollars per share)	[1]	0	(0.01)		0		0.09
Net (loss) income attributable to GCP shareholders (in dollars per share)	[1],[2]	$ (0.02)	$ 0.04		$ 0		$ 0.33
Weighted average number of diluted shares (in shares)		72,900,000	73,000,000.0	[1]	73,000,000.0	[1]	72,900,000	[1]

[1] Dilutive effect is only applicable to the periods during which GCP generated net income from continuing operations.

[2] Amounts may not sum due to rounding.