Accounts payable and accrued liabilities - Accounts Payable and Accrued Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Accounts Payable And Accrued Liabilities [Line Items]
Accounts payable	$ 163.0	$ 196.3
Employee benefits	41.4	45.4
Accrued sales discounts and rebates	15.9	11.8
Environmental remediation and related costs	8.0	8.6
Deferred income	5.5	3.5
Interest	1.1	5.0
Other	48.7	71.7
Total	331.4	363.7
Contran Income Taxes [Member]
Accounts Payable And Accrued Liabilities [Line Items]
Payable to affiliates		0.1
Contran Trade Items [Member]
Accounts Payable And Accrued Liabilities [Line Items]
Payable to affiliates	24.8	21.1
LPC [Member]
Accounts Payable And Accrued Liabilities [Line Items]
Payable to affiliates	22.7
Other [Member]
Accounts Payable And Accrued Liabilities [Line Items]
Payable to affiliates	$ 0.3	$ 0.2