Other Comprehensive Income Comprehensive Income (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 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 Comprehensive Income, Defined Benefit Plan, Other Changes in Funded Status Recognized in Net Periodic Benefit Cost Net of Tax	25.4	(44.5)	53.8	(41.1)
Currency translation adjustments, After-Tax Amount	(16.8)	(15.6)	(23.3)	(9.4)
Other comprehensive income (loss) before reclassifications, Gains and Losses from Hedging Activities			0.3	(1.5)
Other comprehensive income (loss) before reclassifications, Total			30.8	(52.0)
Amounts reclassified from accumulated other comprehensive loss, Defined Benefit Pension and Other Postretirement Plans	7.9	7.1	15.7	13.8
Amounts reclassified from accumulated other comprehensive loss, Gains and Losses from Hedging Activities	(1.0)	1.4	(0.7)	3.0
Amounts reclassified from accumulated other comprehensive loss, Total	6.9	8.5	15.0	16.8
Benefit plans, net, After-Tax Amount	33.3	(37.4)	69.5	(27.3)
Gain (loss) from hedging activities, net of income taxes	(0.8)	1.6	(0.4)	1.5
Other comprehensive income attributable to W. R. Grace & Co. shareholders, After-Tax Amount	15.7	(51.4)	45.8	(35.2)
Ending, Defined Benefit Pension and Other Postretirement Plans	(572.3)	(632.5)	(572.3)	(632.5)
Ending, Currency Translation Adjustments	12.3	20.8	12.3	20.8
Ending, Gains and Losses from Hedging Activities	(0.7)	(1.2)	(0.7)	(1.2)
Ending, Unrealized Loss on Investment	(0.8)	(0.8)	(0.8)	(0.8)
Ending, Total	$ (561.5)	$ (613.7)	$ (561.5)	$ (613.7)