Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
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	$ 0.2
Amortization of net deferred actuarial loss included in net periodic benefit cost, Pre-Tax Amount	11.7	10.0
Other changes in funded status, Pre-Tax Amount	42.9	7.5
Benefit plans, net, Pre-Tax Amount	54.8	17.7
Currency translation adjustments, Pre-Tax Amount	(6.5)	6.2
Gain (loss) from hedging activities, Pre-Tax Amount	0.6	(0.2)
Other comprehensive income attributable to W. R. Grace and Co. shareholders, Pre-Tax Amount	48.9	23.7
Defined benefit pension and other postretirement plans, Tax Benefit/(Expense)
Amortization of net prior service cost 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)	(4.0)	(3.4)
Other changes in funded status, Tax Benefit/(Expense)	(14.5)	(4.1)
Benefit plans, net, Tax Benefit/(Expense)	(18.6)	(7.6)
Currency translation adjustments, Tax Benefit/(Expense)	0	0
Gain (loss) from hedging activities, Tax Benefit/(Expense)	(0.2)	0.1
Other comprehensive income attributable to W. R. Grace and Co. shareholders, Tax Benefit/(Expense)	(18.8)	(7.5)
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)	(0.1)
Amortization of net deferred actuarial loss included in net periodic benefit cost, After-Tax Amount	7.7	6.6
Other changes in funded status, After-Tax Amount	28.4	3.4
Benefit plans, net, After-Tax Amount	(36.2)	(10.1)
Currency translation adjustments, After-Tax Amount	(6.5)	6.2
Gain (loss) from hedging activities, After-Tax Amount	0.4	(0.1)
Other comprehensive income attributable to W. R. Grace & Co. shareholders, After-Tax Amount	$ 30.1	$ 16.2