Business segment information - Segment Operating Performance (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Jun. 30, 2012	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting Information [Line Items]
Net sales	$ 524.5	$ 584.1		$ 1,706.2	$ 1,612.9
Cost of sales	423.2	371.4		1,175.5	1,050.6
Gross margin	101.3	212.7		530.7	562.3
Operating income (loss)	43.8	150.2		353.4	393.3
Equity in earnings of investee	(0.1)	(0.1)		(0.1)	(0.3)
Securities earnings	7.3	6.6		21.5	21.4
Insurance recoveries	1.2	16.1		2.6	16.6
Litigation settlement gain			14.7	14.7
General expenses, net	(7.9)	(9.2)		(37.4)	(32.6)
Gain (loss)on prepayment of debt		0.1		(7.2)	(3.2)
Interest expense	(14.6)	(15.2)		(42.5)	(48.3)
Income before income taxes	29.7	148.5		305.0	346.9
Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales	472.9	547.9		1,579.5	1,505.9
Cost of sales	387.5	337.7		1,070.5	953.5
Gross margin	85.4	210.2		509.0	552.4
Operating income (loss)	40.4	158.4		364.1	407.8
Component products [Member]
Segment Reporting Information [Line Items]
Net sales	37.1	35.8		110.2	105.8
Cost of sales	27.0	27.2		80.6	78.7
Gross margin	10.1	8.6		29.6	27.1
Operating income (loss)	4.4	1.5		11.2	13.4
Waste management [Member]
Segment Reporting Information [Line Items]
Net sales	14.5	0.4		16.5	1.2
Cost of sales	8.7	6.5		24.4	18.4
Gross margin	5.8	(6.1)		(7.9)	(17.2)
Operating income (loss)	$ (1.0)	$ (9.7)		$ (21.9)	$ (27.9)