Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Defined benefit pension and other postretirement plans, Pre-Tax Amount
Amortization of net prior service cost included in net periodic benefit cost, Pre-Tax Amount	$ 0.2	$ 0.3	$ 0.6	$ 0.9
Amortization of net deferred actuarial loss included in net periodic benefit cost, Pre-Tax Amount	10.2	8.7	30.7	26.2
Other changes in funded status, Pre-Tax Amount	(28.4)	(184.6)	(88.8)	(149.4)
Benefit plans, net, Pre-Tax Amount	(18.0)	(175.6)	(57.5)	(122.3)
Currency translation adjustments, Pre-Tax Amount	14.5	(7.6)	5.1	(6.3)
Gain (loss) from hedging activities, Pre-Tax Amount	2.3	(2.6)	4.6	(1.9)
Other comprehensive income (loss) attributable to W. R. Grace and Co. shareholders, Pre-Tax Amount	(1.2)	(185.8)	(47.8)	(130.5)
Defined benefit pension and other postretirement plans, Tax Benefit/(Expense)
Amortization of net prior service credit included in net periodic benefit cost, Tax Benefit/(Expense)	(0.1)	(0.1)	(0.2)	(0.3)
Amortization of net deferred actuarial loss included in net periodic benefit cost, Tax Benefit/(Expense)	(3.5)	(3.0)	(10.5)	(9.0)
Other changes in funded status, Tax Benefit/(Expense)	8.6	64.2	27.9	52.1
Benefit plans, net, Tax Benefit/(Expense)	5.0	61.1	17.2	42.8
Gain (loss) from hedging activities, Tax Benefit/(Expense)	(0.8)	0.9	(1.6)	0.7
Other comprehensive income (loss) attributable to W. R. Grace and Co. shareholders, Tax Benefit/(Expense)	4.2	62.0	15.6	43.5
Defined benefit pension and other postretirement plans, After-Tax Amount:
Amortization of net prior service credit included in net periodic benefit cost, After-Tax Amount	0.1	0.2	0.4	0.6
Amortization of net deferred actuarial loss included in net periodic benefit cost, After-Tax Amount	6.7	5.7	20.2	17.2
Other changes in funded status, After-Tax Amount	(19.8)	(120.4)	(60.9)	(97.3)
Benefit plans, net, After-Tax Amount	(13.0)	(114.5)	(40.3)	(79.5)
Currency translation adjustments, After-Tax Amount	14.5	(7.6)	5.1	(6.3)
Gain (loss) from hedging activities, After-Tax Amount	1.5	(1.7)	3.0	(1.2)
Other comprehensive income (loss) attributable to W. R. Grace & Co. shareholders	$ 3.0	$ (123.8)	$ (32.2)	$ (87.0)