Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 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
Amortization of net deferred actuarial loss included in net periodic benefit cost, Pre-Tax Amount	10.0	9.0
Other changes in funded status, Pre-Tax Amount	7.5	10.9
Benefit plans, net, Pre-Tax Amount	17.7	20.2
Currency translation adjustments, Pre-Tax Amount	6.2	1.8
Gain (loss) from hedging activities, Pre-Tax Amount	(0.2)	1.1
Other comprehensive income (loss) attributable to W. R. Grace and Co. shareholders, Pre-Tax Amount	23.7	23.1
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)
Amortization of net deferred actuarial loss included in net periodic benefit cost, Tax Benefit/(Expense)	(3.4)	(3.1)
Other changes in funded status, Tax Benefit/(Expense)	(4.1)	(3.8)
Benefit plans, net, Tax Benefit/(Expense)	(7.6)	(7.0)
Gain (loss) from hedging activities, Tax Benefit/(Expense)	0.1	(0.4)
Other comprehensive income (loss) attributable to W. R. Grace and Co. shareholders, Tax Benefit/(Expense)	(7.5)	(7.4)
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
Amortization of net deferred actuarial loss included in net periodic benefit cost, After-Tax Amount	6.6	5.9
Other changes in funded status, After-Tax Amount	3.4	7.1
Benefit plans, net, After-Tax Amount	10.1	13.2
Currency translation adjustments, After-Tax Amount	6.2	1.8
Gain (loss) from hedging activities, After-Tax Amount	(0.1)	0.7
Total other comprehensive income attributable to W. R. Grace & Co. shareholders	$ 16.2	$ 15.7