Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
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	$ (3.1)	$ (1.7)	$ 0.7
Amortization of net deferred actuarial loss included in net periodic benefit cost, Pre-Tax Amount	0.7		0.4
Net prior service credit, Pre-Tax Amount	5.7	13.6	1.7
Net Deferred Actuarial Loss Arising During Period, Pre-Tax Amount	(0.4)	1.0	4.3
Other Comprehensive Income, Gain on termination of postretirement plans, Pre-Tax	(4.5)
Benefit plans, net, Pre-Tax Amount	(1.6)	0.7	7.1
Foreign Currency Transaction and Translation Adjustment, Pre-Tax Amount	(43.3)	(28.0)	(23.6)
Other Comprehensive Income Gain (Loss)on curtailment of postretirement plans pretax		(12.2)
Loss from Hedging Activities, Pre-Tax Amount	2.1	(7.1)	(0.3)
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Loss, before Tax, Portion Attributable to Parent		0.8
Loss on Securities Available for Sale, Pre-Tax Amount		(0.1)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Parent			0.1
Other Comprehensive Income (Loss), Attributable to W. R. Grace and Co Shareholders, Pre-Tax Amount	(42.8)	(33.7)	(16.7)
Defined benefit pension and other postretirement plans, Tax Benefit (Expense)
Amortization of Net prior service credit included in net periodic benefit cost, Tax Benefit (Expense)	1.0	0.6	(0.2)
Amortization of Net Deferred Actuarial Gain (Loss), Recognized in Net Periodic Benefit Cost Tax Benefit (Expense)	(0.2)		(0.1)
Net Prior Service Cost (Credit), Tax Benefit (Expense)	(1.9)	(4.8)	(0.6)
Net Deferred Actuarial Loss Arising During Period Tax Benefit (Expense)	0.1	(0.4)	(1.6)
Other Comprehensive Income Gain (Loss)on curtailment of postretirement plans tax		1.3
Other Comprehensive Income, Gain (Loss) on termination of postretirement plans, Tax	1.6
Benefit plans, net Tax Benefit (Expense)	0.6	(3.3)	(2.5)
Currency translation adjustments, Tax Benefit (Expense)	0.0	0.0	0.0
Gain (loss) from hedging activities, Tax Benefit (Expense)	(0.8)	2.6	0.1
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Loss, Tax, Portion Attributable to Parent		0.0
Loss on Securities Available-for-sale Tax Benefit (Expense)		0.0	0.0
Other comprehensive income (loss) attributable to W. R. Grace and Co. shareholders, Tax Benefit (Expense)	(0.2)	(0.7)	(2.4)
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	(2.1)	(1.1)	0.5
Amortization of Net Deferred Actuarial Gain (Loss) Recognized in Net Periodic Benefit Cost After Tax Amount	0.5		0.3
Net Prior Service Cost (Credit) Arising During Period, Net of Tax	3.8	8.8	1.1
Net Deferred Actuarial Loss Arising During Period, Net of Tax	(0.3)	0.6	2.7
Other Comprehensive Income, Gain (Loss) on termination of postretirement plans, Net of Tax	(2.9)
Other Comprehensive Income Gain (Loss)on curtailment of postretirement plans net of tax		(10.9)
Benefit plans, net After-Tax Amount	(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 than Temporary Impairment Losses, Investments, After-Tax Amount	0.0	0.8	0.0
Loss on Securities Available-for-sale, Post Tax Amount		(0.1)
(Loss) gain on securities available for sale, net of income taxes	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)