Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Numerators
Net income attributable to W. R. Grace & Co. shareholders	$ (111.6)		$ 75.5		$ 69.3		$ 60.9		$ 58.1		$ 81.3		$ 75.8		$ 54.2		$ 94.1	$ 269.4	$ 207.1
Denominators
Weighted average common shares-basic calculation																	74.9	73.6	72.7
Dilutive effect of employee stock options (in shares)																	1.4	1.9	1.7
Weighted average common shares-diluted calculation																	76.3	75.5	74.4
Basic earnings per share (in dollars per share)	$ (1.48)	[1]	$ 1.01	[1]	$ 0.93	[1]	$ 0.82	[1]	$ 0.79	[1]	$ 1.10	[1]	$ 1.03	[1]	$ 0.74	[1]	$ 1.26	$ 3.66	$ 2.85
Diluted earnings per share (in dollars per share)	$ (1.48)	[1]	$ 0.99	[1]	$ 0.90	[1]	$ 0.80	[1]	$ 0.77	[1]	$ 1.07	[1]	$ 1.00	[1]	$ 0.72	[1]	$ 1.23	$ 3.57	$ 2.78
Stock options excluded from computation of diluted earnings per share (in shares)																	0.4	1.3	0.9
Number of warrants not included in diluted earnings per share	10																10

[1] Per share results for the four quarters may differ from full-year per share results, as a separate computation of the weighted average number of shares outstanding is made for each quarter presented.