Pension Plans and Other Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Gain on termination and curtailment of pension and other postretirement plans	$ (2.4)	$ 0.0	$ (2.4)	$ 0.0
W.R. Grace
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost (income)				0.1
U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	1.5	0.0	3.0	0.1
Interest cost	1.2	0.2	2.4	0.3
Expected return on plan assets	(1.3)	(0.1)	(2.5)	(0.3)
Amortization of prior service (credit) cost			0.0	0.0
Gain on termination and curtailment of pension and other postretirement plans	0.0	0.0	0.0	0.0
Net periodic benefit cost (income)	1.4	0.1	2.9	0.1
Non-U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0.8	0.7	1.7	1.5
Interest cost	2.0	2.3	4.1	4.6
Expected return on plan assets	(2.2)	(2.7)	(4.5)	(5.5)
Amortization of prior service (credit) cost			0.0	0.1
Gain on termination and curtailment of pension and other postretirement plans	(1.4)	0.0	(1.4)	0.0
Net periodic benefit cost (income)	(0.8)	0.3	(0.1)	0.7
Other Post Retirement
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0.0	0.0	0.0	0.0
Interest cost	0.0	0.0	0.0	0.0
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of prior service (credit) cost			(0.1)	0.0
Gain on termination and curtailment of pension and other postretirement plans	(1.0)	0.0	(1.0)	0.0
Net periodic benefit cost (income)	$ (1.0)	$ 0.0	$ (1.1)	$ 0.0