Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Numerators
Net income attributable to W. R. Grace & Co. shareholders	$ 57.4	$ 136.2	$ 110.1	$ 186.3
Denominators
Weighted average common shares—basic calculation	72,600,000	75,900,000	72,700,000	76,500,000
Dilutive effect of employee stock options	600,000	900,000	600,000	1,000,000
Weighted average common shares—diluted calculation	73,200,000	76,800,000	73,300,000	77,500,000
Basic earnings per share	$ 0.79	$ 1.79	$ 1.51	$ 2.44
Diluted earnings per share	$ 0.78	$ 1.77	$ 1.50	$ 2.40
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	400,000	300,000	400,000	100,000
Stock Repurchase Program, Number of Shares Authorized to be Repurchased	500,000,000		500,000,000		500,000,000
Stock Repurchased During Period, Shares			1,123,508
Payments for Repurchase of Common Stock			$ 108.7	$ 233.7
Minimum [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock Repurchase Program, Period in Force			12 months
Maximum [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock Repurchase Program, Period in Force			24 months