Consolidated Statements of Operations (unaudited) - USD ($) shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Net sales		$ 266.9	$ 296.3	$ 755.2	$ 849.3
Cost of goods sold		161.8	185.9	468.9	539.7
Gross profit		105.1	110.4	286.3	309.6
Selling, general and administrative expenses		66.3	67.3	206.7	219.8
Research and development expenses		4.5	5.2	13.8	15.4
Interest expense and related financing costs		5.7	5.9	17.3	86.4
Repositioning expenses		4.4	3.7	15.6	5.8
Restructuring expenses and asset impairments		3.8	14.3	8.8	13.2
Other income, net		(2.2)	(0.9)	(5.7)	(11.3)
Total costs and expenses		82.5	95.5	256.5	329.3
Income (loss) from continuing operations before income taxes		22.6	14.9	29.8	(19.7)
(Provision for) benefit from income taxes		(5.5)	(7.6)	5.2	(15.8)
Income (loss) from continuing operations		17.1	7.3	35.0	(35.5)
(Loss) income from discontinued operations, net of income taxes		(0.4)	18.2	5.9	26.7
Net income (loss)		16.7	25.5	40.9	(8.8)
Less: Net income attributable to noncontrolling interests		(0.1)	(0.1)	(0.3)	(0.3)
Net income (loss) attributable to GCP shareholders		16.6	25.4	40.6	(9.1)
Amounts Attributable to GCP Shareholders:
Income (loss) from continuing operations attributable to GCP shareholders		17.0	7.2	34.7	(35.8)
(Loss) income from discontinued operations, net of income taxes		$ (0.4)	$ 18.2	$ 5.9	$ 26.7
Basic earnings (loss) per share:
Income (loss) from continuing operations attributable to GCP shareholders (in usd per share)		$ 0.23	$ 0.10	$ 0.48	$ (0.50)
(Loss) income from discontinued operations, net of income taxes (in usd per share)		(0.01)	0.25	0.08	0.37
Net income (loss) attributable to GCP shareholders (in usd per share)	[1]	$ 0.23	$ 0.35	$ 0.56	$ (0.13)
Weighted average number of basic shares (in shares)		72.7	72.2	72.5	72.1
Diluted earnings (loss) per share:
Income (loss) from continuing operations attributable to GCP shareholders (in dollars per share)	[2]	$ 0.23	$ 0.10	$ 0.48	$ (0.50)
(Loss) income from discontinued operations, net of income taxes (in dollars per share)	[2]	(0.01)	0.25	0.08	0.37
Net income (loss) attributable to GCP shareholders (in dollars per share)	[1],[2]	$ 0.23	$ 0.35	$ 0.56	$ (0.13)
Weighted average number of diluted shares (in shares)	[2]	72.8	72.7	72.9	72.1

[1] Amounts may not sum due to rounding.

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