Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Feb. 05, 2015	Feb. 04, 2014
Numerators
Income from continuing operations attributable to W. R. Grace & Co. shareholders	$ 41.2	$ 33.7	$ 89.7	$ 96.5
(Loss) income from discontinued operations, net of income taxes	(1.6)	(19.9)	(10.9)	27.4
Net income attributable to W. R. Grace & Co. shareholders	$ 39.6	$ 13.8	$ 78.8	$ 123.9
Denominators
Weighted average common shares—basic calculation (in shares)	70,300,000	72,100,000	70,500,000	72,500,000
Dilutive effect of employee stock options (in shares)	400,000	600,000	400,000	600,000
Weighted average common shares—diluted calculation (in shares)	70,700,000	72,700,000	70,900,000	73,100,000
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)	$ 0.59	$ 0.47	$ 1.27	$ 1.33
(Loss) income from discontinued operations (in USD per share)	(0.03)	(0.28)	(0.15)	0.38
Net income	0.56	0.19	1.12	1.71
Diluted earnings per share attributable to W. R. Grace & Co. shareholders
Income (Loss) from Continuing Operations, Per Diluted Share	0.58	0.46	1.27	1.32
(Loss) income from discontinued operations, net of income taxes	(0.02)	(0.27)	(0.16)	0.37
Net income	$ 0.56	$ 0.19	$ 1.11	$ 1.69
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock Repurchase Program, Authorized Amount					$ 500.0	$ 500.0
Stock repurchased during period (in shares)			737,922	2,263,121
Cash paid for repurchases of common stock			$ 55.1	$ 220.1
Repurchase of common stock			$ 55.1	$ 220.1
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive options outstanding	1,000,000	600,000	1,000,000	400,000