Business and geographic segments - Segment Operating Performance (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Net sales	$ 427.4	$ 508.7	$ 568.4	$ 582.8	$ 456.7	$ 568.6	$ 558.9	$ 440.9	$ 2,087.3	$ 2,025.1	$ 1,533.5
Cost of sales									1,512.1	1,278.4	1,184.3
Gross margin	55.3	97.4	162.1	260.4	192.9	210.2	197.3	146.3	575.2	746.7	349.2
Operating income (loss)	(2.2)	41.1	103.2	203.3	136.5	149.4	139.1	96.4	345.4	521.4	158.3
Equity in earnings of joint venture General corporate items:									(0.2)	(0.5)	(0.4)
Securities earnings									50.2	28.6	26.3
Insurance recoveries						8.7			3.3	16.9	18.8
Litigation settlement gains									14.7		6.3
Gain on sale of excess property									3.2
Litigation settlement expense											(32.2)
Goodwill impairment	(5.3)								(6.4)
General expenses, net									(45.3)	(40.7)	(29.9)
Loss on prepayment of debt, net			3.7					1.7	(7.2)	(3.1)
Interest expense									(56.3)	(61.8)	(68.4)
Income from continuing operations before income taxes									301.4	460.8	78.8
Depreciation and amortization									69.4	63.8	62.1
Capital expenditures									98.8	146.2	44.7
Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales									1,976.3	1,943.3	1,449.7
Cost of sales									1,418.2	1,197.5	1,106.7
Gross margin									558.1	745.8	343.0
Operating income (loss)									366.8	553.0	183.2
Depreciation and amortization									50.4	50.2	47.4
Capital expenditures									74.9	68.6	37.7
Component Products [Member]
Segment Reporting Information [Line Items]
Net sales									83.2	79.8	76.1
Cost of sales									58.9	55.6	53.7
Gross margin									24.3	24.2	22.4
Operating income (loss)									5.4	6.4	5.9
Depreciation and amortization									5.8	6.8	7.7
Capital expenditures									4.3	3.2	2.1
Waste Management [Member]
Segment Reporting Information [Line Items]
Net sales									27.8	2.0	7.7
Cost of sales									35.0	25.3	23.9
Gross margin									(7.2)	(23.3)	(16.2)
Operating income (loss)									(26.8)	(38.0)	(30.8)
Depreciation and amortization									13.2	6.8	7.0
Capital expenditures									19.6	74.3	4.9
Corporate [Member]
Segment Reporting Information [Line Items]
Capital expenditures										$ 0.1