Chapter 11 Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended		138 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2012 Chapter 11 Filing Entities	Sep. 30, 2011 Chapter 11 Filing Entities	Sep. 30, 2012 Chapter 11 Filing Entities	Sep. 30, 2011 Chapter 11 Filing Entities	Sep. 30, 2012 Chapter 11 Filing Entities	Sep. 30, 2012 Chapter 11 Filing Entities	Dec. 31, 2011 Chapter 11 Filing Entities
Components of liabilities subject to compromise are as follows:
Asbestos-related contingencies	$ 1,700.0		$ 1,700.0		$ 1,700.0		$ 1,700.0		$ 1,700.0		$ 1,700.0		$ 1,700.0
Pre-petition bank debt plus accrued interest	965.3		965.3		941.8		929.5		929.5		929.5		907.3
Environmental contingencies	143.3		143.3		149.9		143.3		143.3		143.3		149.9
Unfunded special pension arrangements	189.6		189.6		185.2		133.0		133.0		133.0		129.0
Income tax contingencies	80.7		80.7		69.3		80.7		80.7		80.7		69.3
Postretirement benefits other than pension							67.2		67.2		67.2		64.6
Drawn letters of credit plus accrued interest							35.8		35.8		35.8		34.5
Accounts payable							31.3		31.3		31.3		31.3
Retained obligations of divested businesses							28.4		28.4		28.4		28.4
Other accrued liabilities	157.6		157.6		149.5		97.9		97.9		97.9		89.8
Reclassification to current liabilities							(10.6)		(10.6)		(10.6)		(8.4)
Total Liabilities Subject to Compromise	3,236.5		3,236.5		3,195.7		3,236.5		3,236.5		3,236.5		3,195.7
Reconciliation of the changes in pre-filing date liability balances
Balance, Filing Date April 2, 2001											2,366.0	2,366.0
Cash disbursements and/or reclassifications under Bankruptcy Court orders:
Payment of environmental settlement liability			8.1	7.7							(252.0)
Freight and distribution order											(5.7)
Trade accounts payable order											(9.1)
Resolution of contingencies subject to Chapter 11											(130.0)
Other court orders for payments of certain operating expenses											(372.4)
Expense/(income) items:
Interest on pre-petition liabilities											539.5
Employee-related accruals											125.6
Provision for asbestos-related contingencies											744.8
Provision for environmental contingencies											353.4
Provision for income tax contingencies											(87.3)
Balance sheet reclassifications											(36.3)
Balance, end of period											3,236.5
Chapter 11 Expenses
Legal and financial advisory fees							4.6	4.5	13.2	17.3
Interest (income) expense							(0.2)	(0.1)	(0.6)	(0.4)
Chapter 11 expenses, net of interest income	4.4	4.4	12.6	16.9			4.4	4.4	12.6	16.9
Debtor-in-Possession Statements of Operations
Net sales, including intercompany	776.6	864.2	2,357.7	2,386.3					1,153.8	1,046.2
Cost of goods sold, including intercompany, exclusive of depreciation and amortization shown separately below									685.2	652.3
Selling, general and administrative expenses	130.8	148.2	401.2	424.0					192.8	210.8
Defined benefit pension expense	17.6	15.9	53.2	47.5					38.0	32.7
Depreciation and amortization			88.9	89.9					50.4	51.1
Chapter 11 expenses, net of interest income	4.4	4.4	12.6	16.9			4.4	4.4	12.6	16.9
Libby medical program settlement	0.1		19.6						19.6
Research and development expenses	15.4	16.8	47.9	49.1					26.8	27.4
Interest expense and related financing costs	11.5	11.1	34.1	32.5					30.8	29.8
Restructuring expenses			5.4						2.5	0.9
Provision for environmental remediation	0.6	1.1	1.8	1.6					1.1	1.7
Other income, net	(3.2)	2.7	(6.0)	0.8					(63.2)	(56.9)
Total costs and expenses	173.4	194.8	557.0	560.2					996.6	966.7
Income before income taxes and equity in net income of non-filing entities									157.2	79.5
Provision for income taxes	(35.4)	(40.4)	(102.0)	(102.5)					(60.4)	(30.6)
Income before equity in net income of non-filing entities									96.8	48.9
Equity in net income of non-filing entities									108.9	162.4
Net income attributable to W. R. Grace & Co. shareholders	75.5	81.3	205.7	211.3					205.7	211.3
OPERATING ACTIVITIES
Net income attributable to W. R. Grace and Co. shareholders	75.5	81.3	205.7	211.3					205.7	211.3
Reconciliation to net cash provided by operating activities:
Depreciation and amortization			88.9	89.9					50.4	51.1
Equity in net income of non-filing entities									(108.9)	(162.4)
Provision for income taxes	35.4	40.4	102.0	102.5					60.4	30.6
Income taxes paid, net of refunds			(41.6)	(38.3)					(2.9)	(12.3)
Libby medical program settlement	0.1		19.6						19.6
Libby medical program settlement paid			(19.6)						(19.6)
Tax benefits from stock-based compensation			(23.0)						(23.0)
Defined benefit pension expense	17.6	15.9	53.2	47.5					38.0	32.7
Payments under defined benefit pension arrangements			(122.5)	(260.0)					(113.5)	(250.0)
Changes in assets and liabilities, excluding the effect of foreign currency translation:
Trade accounts receivable			(3.7)	(86.8)					(7.6)	(32.6)
Inventories			20.6	(89.3)					45.0	(48.6)
Accounts payable			(6.0)	54.8					(13.5)	36.8
All other items, net			(10.2)	7.7					7.7	60.6
Net cash provided by (used for) operating activities									137.8	(82.8)
INVESTING ACTIVITIES
Capital expenditures			(94.0)	(97.1)					(57.1)	(52.5)
Transfer to restricted cash and cash equivalents			(24.1)	(27.7)					(13.2)	(6.8)
Net cash used for investing activities									(70.3)	(59.3)
FINANCING ACTIVITIES
Net borrowings under credit arrangements			24.6	10.0					(0.4)	(0.6)
Proceeds from exercise of stock options			25.7	10.3					25.7	10.3
Tax benefits from stock-based compensation			23.0						23.0
Net cash provided by financing activities									48.3	9.7
Net increase (decrease) in cash and cash equivalents									115.8	(132.4)
Cash and cash equivalents, beginning of period			1,048.3	1,015.7					788.6	787.2
Cash and cash equivalents, end of period	1,251.2	923.8	1,251.2	923.8			904.4	654.8	904.4	654.8	904.4
Current Assets
Cash and cash equivalents	1,251.2	923.8	1,251.2	923.8			904.4	654.8	904.4	654.8	904.4
Restricted cash and cash equivalents	160.6		160.6		136.5		96.1		96.1		96.1		82.9
Trade accounts receivable, net	471.2		471.2		461.8		133.1		133.1		133.1		125.5
Accounts receivable-unconsolidated affiliate	12.2		12.2		11.2		11.1		11.1		11.1		10.2
Receivables from non-filing entities, net							169.7		169.7		169.7		143.1
Inventories	309.0		309.0		329.1		115.0		115.0		115.0		160.0
Other current assets	95.1		95.1		93.0		65.8		65.8		65.8		67.3
Total Current Assets	2,358.1		2,358.1		2,146.4		1,495.2		1,495.2		1,495.2		1,377.6
Properties and equipment, net	735.4		735.4		723.5		426.1		426.1		426.1		418.8
Deferred income taxes	756.5		756.5		759.4		737.3		737.3		737.3		752.7
Asbestos-related insurance	500.0		500.0		500.0		500.0		500.0		500.0		500.0
Loans receivable from non-filing entities, net							340.7		340.7		340.7		362.3
Investment in non-filing entities							429.6		429.6		429.6		333.6
Investment in unconsolidated affiliate	81.2		81.2		70.8		81.2		81.2		81.2		70.8
Other assets	38.0		38.0		38.0		61.1		61.1		61.1		63.7
Total Assets	4,756.5		4,756.5		4,494.0		4,071.2		4,071.2		4,071.2		3,879.5
Liabilities Not Subject to Compromise
Current liabilities (including $XX due to unconsolidated affiliate) (2011-$3.5)	634.2		634.2		632.9		248.2		248.2		248.2		250.7
Underfunded defined benefit pension plans							137.4		137.4		137.4		215.5
Other liabilities (including $XX due to unconsolidated affiliate) (2011-$18.3)	43.6		43.6		49.1		56.2		56.2		56.2		58.1
Total Liabilities Not Subject to Compromise	1,117.8		1,117.8		1,130.8		441.8		441.8		441.8		524.3
Liabilities Subject to Compromise	3,236.5		3,236.5		3,195.7		3,236.5		3,236.5		3,236.5		3,195.7
Total Liabilities	4,354.3		4,354.3		4,326.5		3,678.3		3,678.3		3,678.3		3,720.0
Total W. R. Grace & Co. Shareholders' Equity	392.8		392.8		159.4		392.8		392.8		392.8		159.4
Noncontrolling interests in Chapter 11 filing entities	9.4		9.4		8.1		0.1		0.1		0.1		0.1
Total Equity	402.2	75.7	402.2	75.7	167.5	(68.8)	392.9		392.9		392.9		159.5
Total Liabilities and Equity	4,756.5		4,756.5		4,494.0		4,071.2		4,071.2		4,071.2		3,879.5
Due to unconsolidated affiliate, current							3.6		3.6		3.6		3.5
Due to unconsolidated affiliate, noncurrent							$ 22.1		$ 22.1		$ 22.1		$ 18.3