Other Comprehensive Income (Loss) (Details 2) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2015	Dec. 31, 2015 country	Dec. 31, 2012 USD ($)
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	$ 3.0	$ 4.0	$ 6.6			$ 2.0
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	(66.1)	(22.8)	5.2			28.8
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	(3.7)	(5.0)	(0.5)			(0.3)
Accumulated Other Comprehensive Income (Loss), Unrealized loss on investment	0.0	0.0	(0.8)			(0.8)
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	0.0	0.0	0.1			0.0
Accumulated Other Comprehensive Income (Loss), Net of Tax	(66.8)	(23.8)	10.6			$ 29.7
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Reclassification Adjustments, Net of Tax	3.5	9.4	3.8
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, before Reclassification Adjustments, Net of Tax	(43.3)	(28.0)	(23.6)
Other Comprehensive Income (Loss), Before Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0.6	(3.2)	1.2
Other Comprehensive Income Loss, before Reclassification, Unrealized Loss on Investment, Net Of Tax	0.0	0.0	0.0
Other Comprehensive Income Loss before Reclassification Adjustment For Sale Of Securities Included In Net Income Net Of Tax	0.0	(0.7)	0.1
Other Comprehensive Income (loss) Before Reclassifications, Net of Tax	(39.2)	(22.5)	(18.5)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	(4.5)	(12.0)	0.8
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment Realized upon Sale or Liquidation, Net of Tax	0.0	0.0	0.0
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax	0.7	(1.3)	(1.4)
Reclassification from Accumulated Other Comprehensive Income (Loss), Unrealized loss on investment	0.0	0.8	0.0
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Net of Tax	0.0	0.6	0.0
Other Comprehensive Income Loss Reclassification Adjustment Net Of Tax	3.8	11.9	0.6
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax, Portion Attributable to Parent	1.0	2.6	(4.6)
Currency Transaction and Translation Adjustment, Net of Tax	(43.3)	(28.0)	(23.6)
Gain (loss) from hedging activities, Net of Tax	1.3	(4.5)	(0.2)
Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During period, Net of Tax, Portion Attributable to Parent	0.0	(0.8)	0.0
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent	0.0	(0.1)	0.1
Other comprehensive income (loss) attributable to W. R. Grace & Co. shareholders, Net of Tax	$ (43.0)	$ (34.4)	$ (19.1)
Defined benefit pension and other postretirement plans:
Number of countries in which the entity has operations				50	40