Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Feb. 05, 2015	Feb. 04, 2014
Numerators
Income from continuing operations attributable to W. R. Grace & Co. shareholders	$ 38.1		$ 32.6	$ 48.5	$ 62.8
Income (loss) from discontinued operations, net of income taxes	0.6		24.8	(9.3)	47.3
Net income attributable to W. R. Grace & Co. shareholders	$ 38.7	$ 0.5	$ 57.4	$ 39.2	$ 110.1
Denominators
Weighted average common shares—basic calculation (in shares)	70,500,000		72,600,000	70,500,000	72,700,000
Dilutive effect of employee stock options (in shares)	400,000		600,000	500,000	600,000
Weighted average common shares—diluted calculation (in shares)	70,900,000	71,100,000	73,200,000	71,000,000	73,300,000
Basic earnings per share attributable to W. R. Grace & Co. shareholders
Net income from continuing operations attributable to W. R. Grace & Co. shareholders (in USD per share)	$ 0.54	$ 0.14	$ 0.45	$ 0.69	$ 0.86
(Loss) income from discontinued operations (in USD per share)	0.01		0.34	(0.13)	0.65
Net income	0.55	0.01	0.79	0.56	1.51
Diluted earnings per share attributable to W. R. Grace & Co. shareholders
Income (Loss) from Continuing Operations, Per Diluted Share	0.54	0.14	0.45	0.68	0.86
Income (loss) from discontinued operations, net of income taxes	0.01		0.33	(0.13)	0.64
Net income	$ 0.55	$ 0.01	$ 0.78	$ 0.55	$ 1.50
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive options outstanding	1,000,000		400,000	1,200,000	400,000
Stock Repurchase Program, Authorized Amount						$ 500.0	$ 500.0
Stock repurchased during period (in shares)				472,400	1,123,508
Cash paid for repurchases of common stock				$ 35.1	$ 108.7