Chapter 11 Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended				3 Months Ended			9 Months Ended			150 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2013 Chapter 11 Filing Entities		Sep. 30, 2012 Chapter 11 Filing Entities	Sep. 30, 2013 Chapter 11 Filing Entities		Sep. 30, 2012 Chapter 11 Filing Entities	Sep. 30, 2013 Chapter 11 Filing Entities		Dec. 31, 2012 Chapter 11 Filing Entities		Apr. 02, 2001 Chapter 11 Filing Entities
Components of liabilities subject to compromise are as follows:
Asbestos-related contingencies	$ 2,065.0		$ 2,065.0		$ 2,065.0		$ 2,065.0			$ 2,065.0			$ 2,065.0		$ 2,065.0
Pre-petition bank debt plus accrued interest	997.5		997.5		973.3		960.1			960.1			960.1		937.2
Environmental contingencies	134.0		134.0		140.5		134.0			134.0			134.0		140.5
Unfunded special pension arrangements	174.8		174.8		188.1		127.4			127.4			127.4		134.3
Income tax contingencies	85.4		85.4		87.6		85.4			85.4			85.4		87.6
Postretirement benefits other than pension							58.4			58.4			58.4		63.9
Drawn letters of credit plus accrued interest							37.4			37.4			37.4		36.1
Accounts payable							31.3			31.3			31.3		31.3
Retained obligations of divested businesses							29.6			29.6			29.6		29.0
Other accrued liabilities	169.7		169.7		162.6		108.8			108.8			108.8		102.3
Reclassification to current liabilities							(11.0)	[1]		(11.0)	[1]		(11.0)	[1]	(10.1)	[1]
Liabilities Subject to Compromise	3,626.4		3,626.4		3,617.1		3,626.4			3,626.4			3,626.4		3,617.1
Reconciliation of the changes in pre-filing date liability balances
Balance, Filing Date April 2, 2001																	2,366.0
Cash disbursements and/or reclassifications under Bankruptcy Court orders:
Payment of environmental settlement liability			(11.2)	(8.1)									(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													(395.4)
Expense/(income) items:
Interest on pre-petition liabilities													578.0
Employee-related accruals													125.2
Provision for asbestos-related contingencies													1,109.8
Provision for environmental contingencies													359.0
Provision for income tax contingencies													(82.7)
Balance sheet reclassifications													(36.7)
Balance, end of period							3,626.4			3,626.4			3,626.4				2,366.0
Chapter 11 Expenses
Legal and financial advisory fees							3.6		4.6	12.4		13.2
Interest income							(0.7)		(0.2)	(1.4)		(0.6)
Chapter 11 expenses, net of interest income	2.9	4.4	11.0	12.6			2.9		4.4	11.0		12.6
Debtor-in-Possession Statements of Operations
Net sales, including intercompany	771.3	776.6	2,284.0	2,357.7						1,077.1		1,153.8
Cost of goods sold, including intercompany, exclusive of depreciation and amortization shown separately below										659.0		685.2
Selling, general and administrative expenses	125.2	130.8	391.7	401.2						175.5		192.8
Defined benefit pension expense	18.2	17.6	54.9	53.2						35.9		38.0
Depreciation and amortization			91.8	88.9						51.4		50.4
Chapter 11 expenses, net of interest income	2.9	4.4	11.0	12.6			2.9		4.4	11.0		12.6
Libby medical program settlement paid	0	(19.6)							(19.6)	0		19.6
Research and development expenses	15.0	15.4	48.5	47.9						27.8		26.8
Interest expense and related financing costs	10.7	11.5	32.1	34.1						28.1		30.8
Restructuring expenses			6.0							4.8		2.5
Provision for environmental remediation	1.7	0.6	4.0	1.8						3.8		1.1
Other income, net	0.7	(3.2)	5.1	(6.0)						(52.2)		(63.2)
Total costs and expenses	175.2	173.4	538.9	557.0						945.1		996.6
Income before income taxes and equity in net income of non-filing entities										132.0		157.2
Provision for income taxes	(39.8)	(35.4)	(106.7)	(102.0)						(52.9)		(60.4)
Income before equity in net income of non-filing entities										79.1		96.8
Equity in net income of non-filing entities										126.0		108.9
Net income attributable to W. R. Grace & Co. shareholders	69.4	75.5	205.1	205.7						205.1		205.7
Operating Activities
Net income attributable to W. R. Grace and Co. shareholders	69.4	75.5	205.1	205.7						205.1		205.7
Reconciliation to net cash provided by operating activities:
Depreciation and amortization			91.8	88.9						51.4		50.4
Equity in net income of non-filing entities										(126.0)		(108.9)
Provision for income taxes	39.8	35.4	106.7	102.0						52.9		60.4
Income taxes paid, net of refunds			(65.6)	(41.6)						(3.6)		(2.9)
Libby medical program settlement	0	0.1	0	19.6								19.6
Defined benefit pension expense	18.2	17.6	54.9	53.2						35.9		38.0
Payments under defined benefit pension arrangements			(63.6)	(122.5)						(54.2)		(113.5)
Changes in assets and liabilities, excluding the effect of foreign currency translation:
Trade accounts receivable			5.2	(3.7)						(7.5)		(7.6)
Inventories			(37.7)	20.6						(31.8)		45.0
Accounts payable			6.8	3.6						7.5		(7.2)
All other items, net			(7.1)	(10.2)						14.8		(22.3)
Net cash provided by (used for) operating activities										206.3		144.1
Tax benefits from stock-based compensation	33.7	(23.0)							(23.0)			(33.7)
Investing Activities
Capital expenditures			(117.9)	(103.6)						(68.6)		(63.4)
Short-term Investments	(500.0)	0	(500.0)	0	0		(500.0)		0	(500.0)		0	(500.0)		0
Transfer to restricted cash and cash equivalents			12.4	(24.1)						(11.2)		(13.2)
Net cash used for investing activities										(579.8)		(76.6)
Financing activities
Net repayments under credit arrangements			(3.0)	24.6						(0.3)		(0.4)
Proceeds from exercise of stock options			30.9	25.7						31.7		25.7
Excess tax benefits from stock-based compensation	(33.7)	23.0										(33.7)
Net cash provided by financing activities										(2.3)		48.3
Net decrease in cash and cash equivalents										(375.8)		115.8
Cash and cash equivalents, beginning of period			1,336.9	1,048.3						1,064.2		788.6
Cash and cash equivalents, end of period	1,054.7	1,251.2	1,054.7	1,251.2			688.4		904.4	688.4		904.4	688.4
Current Assets
Cash and cash equivalents	1,054.7	1,251.2	1,054.7	1,251.2			688.4		904.4	688.4		904.4	688.4
Restricted cash and cash equivalents	185.2		185.2		197.6		129.5			129.5			129.5		118.3
Trade accounts receivable, net	467.8		467.8		474.8		140.1			140.1			140.1		132.6
Accounts receivable—unconsolidated affiliate	16.1		16.1		15.6		14.9			14.9			14.9		14.1
Receivables from non-filing entities, net							154.1			154.1			154.1		160.5
Inventories	314.8		314.8		278.6		138.1			138.1			138.1		106.3
Other current assets	140.4		140.4		78.4		15.7			15.7			15.7		58.5
Total Current Assets	2,689.6		2,689.6		2,440.2		1,780.8			1,780.8			1,780.8		1,654.5
Properties and equipment, net	787.8		787.8		770.5		449.5			449.5			449.5		433.5
Deferred income taxes	814.6		814.6		956.3		788.0			788.0			788.0		935.5
Asbestos-related insurance	500.0		500.0		500.0		500.0			500.0			500.0		500.0
Loans receivable from non-filing entities, net							286.5			286.5			286.5		282.1
Investment in non-filing entities							556.3			556.3			556.3		449.5
Investment in unconsolidated affiliate	90.8		90.8		85.5		90.8			90.8			90.8		85.5
Other assets	36.1		36.1		24.5		58.1			58.1			58.1		47.2
Total Assets	5,230.0		5,230.0		5,090.2		4,510.0			4,510.0			4,510.0		4,387.8
Liabilities Not Subject to Compromise
Current liabilities (including $15.0 due to unconsolidated affiliate) (2012—$6.0)	640.3		640.3		646.3		209.6			209.6			209.6		244.7
Underfunded defined benefit pension plans							13.4			13.4			13.4		161.0
Other liabilities (including $24.1 due to unconsolidated affiliate) (2012—$22.4)	45.2		45.2		45.0		58.7			58.7			58.7		56.5
Total Liabilities Not Subject to Compromise	991.7		991.7		1,154.8		281.7			281.7			281.7		462.2
Liabilities Subject to Compromise	3,626.4		3,626.4		3,617.1		3,626.4			3,626.4			3,626.4		3,617.1
Total Liabilities	4,618.1		4,618.1		4,771.9		3,908.1			3,908.1			3,908.1		4,079.3
Total W. R. Grace & Co. Shareholders' Equity	601.8		601.8		308.4		601.8			601.8			601.8		308.4
Noncontrolling interests in Chapter 11 filing entities	10.1		10.1		9.9		0.1			0.1			0.1		0.1
Total Equity	611.9	402.2	611.9	402.2	318.3	167.5	601.9			601.9			601.9		308.5
Total Liabilities and Equity	5,230.0		5,230.0		5,090.2		4,510.0			4,510.0			4,510.0		4,387.8
Interest accrued on pre-petition liabilities subject to compromise			$ 28.1	$ 30.0						$ 28.1		$ 30.0

[1] (1)As of September 30, 2013, and December 31, 2012, approximately $11.0 million and $10.1 million, respectively, of certain pension and postretirement benefit obligations subject to compromise have been presented in "other current liabilities" in the Consolidated Balance Sheets in accordance with ASC 715 "Compensation—Retirement Benefits".