Income Taxes (Details 3) (USD $) In Millions, unless otherwise specified	1 Months Ended				12 Months Ended
	Nov. 30, 2011	Jul. 31, 2011	Apr. 30, 2010	Mar. 31, 2010	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010		Jan. 24, 2011	Dec. 31, 2009
Income Tax Disclosure [Abstract]
Amount of unrecognized tax benefits					$ 88.6		$ 69.3		$ 93.8
Amount of unrecognized tax benefits, excluding interest and penalties					83.1		62.4		79.2
Roll forward of uncertain tax positions
Additions for current year tax positions					3.4		0.6		0.7
Additions for prior year tax positions					22.0		0.5		5.1
Reductions for prior year tax positions and reclassifications	(10.6)				(0.8)		(17.8)	[1],[2]	(18.0)	[3],[4]
Settlements					(1.0)	[5]	(0.1)		(6.3)	[3]
Reductions for expirations of statute of limitations					(2.9)				(0.7)
Balance at the end of the period					83.1		62.4		79.2			98.4
Amount of tax benefit recorded				16.9
Interest reduction in preliminary tax and interest calculation			4.7
Amount of interest refunds received		7.5
Amount of additional interest benefit		2.8
Amount of additional interest benefit recorded net of tax		1.8
Income tax settlement for prior period											15.0
States taxes settled					9.7
States taxes, net of the federal income tax benefit, settled					6.3
Interest accrued settled					5.4
Interest accrued, net of the federal income tax benefit, settled					3.5
Income tax benefit on settlement									10.0
Amount of uncertain tax position reversed	10.6				0.8		17.8	[1],[2]	18.0	[3],[4]
Amount of uncertain tax positions reclassified to income taxes payable							6.7
Material change to aggregate recorded liabilities for uncertain tax positions in the next twelve months
Unrecognized tax benefits, net of indemnification					82.1
Indemnification assets that would be indemnified by a third party					1.0
Accrued interest and penalties related to uncertain tax positions					5.5		6.9		14.6
Non-US tax positions open to examination
Material change to aggregate recorded liabilities for uncertain tax positions in the next twelve months
Material changes to uncertain tax positions, upper range					81
Expected recognition of a deferred charge					4.2
Examination issues and settlements with U.S. federal, state, and foreign tax authorities
Material change to aggregate recorded liabilities for uncertain tax positions in the next twelve months
Decrease in unrecognized tax benefits during the next 12 months					$ 78

[1] On November 3, 2011, Grace received notice from the Canadian Revenue Agency that they had completed a review of Grace's Canadian transfer pricing for the years 2002, 2003, and 2004. As a result, Grace reversed $10.6 million of uncertain tax positions because they were effectively settled pursuant to ASC 740-10-25. A tax matter is effectively settled through examination when the taxing authority has completed an examination; the entity does not intend to appeal or litigate any aspect of a particular tax position for completed examination; and based on a tax authority's widely understood policy, the entity considers it remote that the taxing authority would subsequently examine or reexamine any of the positions once the examination process is completed.

[2] In 2011, $6.7 million of uncertain tax positions representing pre-petition federal and state settlements were reclassified to income taxes payable.

[3] On December 3, 2010, Grace and the Commissioner of the Department of Revenue for the Commonwealth of Massachusetts entered into a settlement agreement resolving all claims for pre-petition taxes and interest for the taxable years 1990 through the petition date. As an inducement to settlement, the Commonwealth waived the right to post-petition interest in exchange for immediate payment and settlement. Based upon the Commonwealth of Massachusetts' agreement to settle, Grace filed a motion with the Bankruptcy Court on December 6, 2010, to release funds for settlement. On January 6, 2011, the U.S. Bankruptcy Court approved the settlement and on January 24, 2011, Grace made payment of $15.0 million to the Commonwealth of Massachusetts. The total amount of state taxes and accrued interest settled on these claims was $9.7 million ($6.3 million net of the federal income tax benefit) and $5.4 million ($3.5 million net of the federal income tax benefit), respectively. As a result of the settlement, Grace recorded an income tax benefit of $10.0 million in 2010.

[4] On February 18, 2010, the Joint Committee on Taxation of the U.S. Congress (JCT) approved the settlement relating to the carryback of remaining NOLs from 1998 to the tax years 1990 through 1996, which resulted in a refund. Grace recorded a tax benefit in the amount of $16.9 million in March 2010. The recorded tax benefit included Grace's estimate of interest payable to Grace. On April 28, 2010, Grace received a preliminary tax and interest calculation from the Internal Revenue Service (IRS) that included approximately $4.7 million less interest than Grace included in the recorded tax benefit because it did not include the benefit of interest netting. In 2010, Grace filed a claim for refund in order to take advantage of interest netting. In July 2011, Grace received interest refunds in the amount of $7.5 million from the IRS and recorded the benefit of the additional IRS interest of $2.8 million ($1.8 million net of tax).

[5] In 2012, $1.0 million of uncertain tax positions representing withholding taxes due were paid as a result of the completion of Grace's Canadian audit for the years 2002, 2003, and 2004.