Revenue Recognition - Schedule of Disaggregates of Net Sales of our Chemicals Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Net sales	$ 455.2	$ 496.5	$ 1,431.4	$ 1,383.6
Chemicals
Disaggregation Of Revenue [Line Items]
Net sales	410.3	464.5	1,312.5	1,275.7
Point of Origin | Chemicals
Disaggregation Of Revenue [Line Items]
Net sales	410.3	464.5	1,312.5	1,275.7
Point of Origin | Chemicals | Germany
Disaggregation Of Revenue [Line Items]
Net sales	211.9	256.6	704.1	672.1
Point of Origin | Chemicals | United States
Disaggregation Of Revenue [Line Items]
Net sales	234.5	209.3	640.2	623.6
Point of Origin | Chemicals | Canada
Disaggregation Of Revenue [Line Items]
Net sales	82.3	70.4	236.1	228.2
Point of Origin | Chemicals | Belgium
Disaggregation Of Revenue [Line Items]
Net sales	66.4	75.6	205.0	205.7
Point of Origin | Chemicals | Norway
Disaggregation Of Revenue [Line Items]
Net sales	49.8	58.2	159.4	156.8
Point of Origin | Chemicals | Eliminations
Disaggregation Of Revenue [Line Items]
Net sales	(234.6)	(205.6)	(632.3)	(610.7)
Point of Destination | Chemicals
Disaggregation Of Revenue [Line Items]
Net sales	410.3	464.5	1,312.5	1,275.7
Point of Destination | Chemicals | Europe
Disaggregation Of Revenue [Line Items]
Net sales	191.8	246.0	664.2	652.3
Point of Destination | Chemicals | North America
Disaggregation Of Revenue [Line Items]
Net sales	142.0	131.4	412.6	393.5
Point of Destination | Chemicals | Other
Disaggregation Of Revenue [Line Items]
Net sales	$ 76.5	$ 87.1	$ 235.7	$ 229.9