Other Comprehensive Income Comprehensive Income (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Increase (Decrease) in Accumulated Other Comprehensive Loss [Roll Forward]
Beginning, Defined Benefit Pension and Other Postretirement Plans	$ 641.8	$ 605.2
Beginning, Currency Translation Adjustments	35.6	30.2
Beginning, Gains and Losses from Hedging Activities	(0.3)	(2.7)
Beginning, Unrealized Loss on Investment	(0.8)	(0.8)
Beginning, Total	(607.3)	(578.5)
Other changes in funded status, After-Tax Amount	28.4	3.4
Currency translation adjustments, After-Tax Amount	(6.5)	6.2
Other comprehensive income (loss) before reclassifications, Gains and Losses from Hedging Activities	(0.1)	1.7
Other comprehensive income (loss) before reclassifications, Total	(22.0)	(7.9)
Amounts reclassified from accumulated other comprehensive loss, Defined Benefit Pension and Other Postretirement Plans	(7.8)	(6.7)
Amounts reclassified from accumulated other comprehensive loss, Gains and Losses from Hedging Activities	(0.3)	(1.6)
Amounts reclassified from accumulated other comprehensive loss, Total	(8.1)	(8.3)
Benefit plans, net, After-Tax Amount	(36.2)	(10.1)
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
Ending, Defined Benefit Pension and Other Postretirement Plans	605.6	595.1
Ending, Currency Translation Adjustments	29.1	36.4
Ending, Gains and Losses from Hedging Activities	0.1	(2.8)
Ending, Unrealized Loss on Investment	(0.8)	(0.8)
Ending, Total	$ (577.2)	$ (562.3)