Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 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	$ 0.6	$ 0.6
Amortization of net deferred actuarial loss included in net periodic benefit cost, Pre-Tax Amount	11.5	10.2	34.8	30.7
Other Comprehensive Income, Defined Benefit Plan, Other Changes in Funded Status Recognized in Net Periodic Benefit Cost, before Tax	33.5	(28.4)	116.6	(88.8)
Benefit plans, net, Pre-Tax Amount	45.2	(18.0)	152.0	(57.5)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Parent	5.0	14.5	(18.3)	5.1
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Portion Attributable to Parent	0.1	2.3	(0.6)	4.6
Other comprehensive income attributable to W. R. Grace and Co. shareholders, Pre-Tax Amount	50.3	(1.2)	133.1	(47.8)
Defined benefit pension and other postretirement plans, Tax Benefit/(Expense)
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Pension Cost, Tax	(0.2)	(0.1)	(0.3)	(0.2)
Other Comprehensive Income, Amortization of Defined Benefit Plan, Net Deferred Actuarial Gain (Loss), Recognized in Net Periodic Benefit Cost Tax Effect	(3.8)	(3.5)	(11.7)	(10.5)
Other Comprehensive Income, Defined Benefit Plan, Other Changes in Funded Status Recognized in Net Periodic Benefit Cost Tax Effect	(12.4)	8.6	(41.7)	27.9
Benefit plans, net, Tax Benefit/(Expense)	(16.4)	5.0	(53.7)	17.2
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Portion Attributable to Parent	0	0	0	0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax, Portion Attributable to Parent	(0.1)	(0.8)	0.2	(1.6)
Other comprehensive income attributable to W. R. Grace and Co. shareholders, Tax Benefit/(Expense)	(16.5)	4.2	(53.5)	15.6
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	(0.1)	0.3	(0.4)
Amortization of net deferred actuarial loss included in net periodic benefit cost, After-Tax Amount	7.7	6.7	23.1	20.2
Other changes in funded status, After-Tax Amount	21.1	(19.8)	74.9	(60.9)
Benefit plans, net, After-Tax Amount	28.8	(13.0)	98.3	(40.3)
Currency translation adjustments, After-Tax Amount	5.0	14.5	(18.3)	5.1
Gain (loss) from hedging activities, net of income taxes	0	1.5	(0.4)	3.0
Other comprehensive income attributable to W. R. Grace & Co. shareholders, After-Tax Amount	$ 33.8	$ 3.0	$ 79.6	$ (32.2)