Consolidated Statements of Equity (unaudited) (Parenthetical) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Statement of Stockholders' Equity [Abstract]
Share repurchases (in shares)		15,800	125,400
Share repurchases	[1]	$ 0.3	$ 3.2
Cash payments for tax withholding obligations		$ 0.3	$ 3.2

[1] During the three months ended March 31, 2020 and 2019, GCP withheld and retained approximately 15,800 shares and 125,400 shares, respectively, of Company common stock in a non-cash transaction with a cost of $0.3 million and $3.2 million, respectively, in connection with fulfilling statutory tax withholding requirements for employees under the provisions of the Company's equity compensation programs. During the three months ended March 31, 2020 and 2019, cash payments for such tax withholding obligations were $0.3 million and $3.2 million, respectively.