Other assets - Summary of Financial Information (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	Dec. 31, 2012 LPC [Member]	Dec. 31, 2011 LPC [Member]	Dec. 31, 2010 LPC [Member]	Dec. 31, 2012 LPC [Member] Kronos Worldwide, Inc. [Member]	Dec. 31, 2011 LPC [Member] Kronos Worldwide, Inc. [Member]	Dec. 31, 2010 LPC [Member] Kronos Worldwide, Inc. [Member]	Dec. 31, 2012 LPC [Member] Tioxide [Member]	Dec. 31, 2011 LPC [Member] Tioxide [Member]	Dec. 31, 2010 LPC [Member] Tioxide [Member]	Sep. 30, 2012 Basic Management and Landwell [Member]	Sep. 30, 2011 Basic Management and Landwell [Member]	Sep. 30, 2010 Basic Management and Landwell [Member]
Financial Information [Line Items]
Current assets	$ 1,363.4				$ 944.2				$ 1,363.4	$ 944.2		$ 139.8	$ 108.5								$ 25.7	$ 16.1
Total revenues																					10.4	10.0	6.9
Prepaid costs and other																					11.6	19.9
Loss before income taxes									301.4	460.8	78.8										(1.2)	(2.7)	(4.6)
Property and equipment, net	763.1				723.8				763.1	723.8	646.1	126.0	140.7								6.4	6.5
Investment in undeveloped land and water rights																					42.0	40.4
Land and development costs																					12.7	13.5
Total assets	3,170.5				2,838.0				3,170.5	2,838.0	2,714.3	265.8	249.2								98.4	96.4
Current liabilities	398.5				415.6				398.5	415.6											14.2	5.7
Other liabilities, primarily current	42.5				71.7				42.5	71.7		43.2	68.0
Long-term debt	880.5				717.4				880.5	717.4											14.3	16.2
Partners' equity												222.6	181.2
Deferred income taxes	454.8				457.2				454.8	457.2											6.0	5.9
Other noncurrent liabilities	78.3				55.4				78.3	55.4											3.4	6.7
Equity	733.6				657.2				733.6	657.2											60.5	61.9
Total liabilities and equity	3,170.5				2,838.0				3,170.5	2,838.0		265.8	249.2								98.4	96.4
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	477.7	290.5	268.2	250.2	144.8	133.7	227.5	145.7	134.5
Cost of sales									1,512.1	1,278.4	1,184.3	477.3	290.1	267.7
General and administrative									273.3	268.9	227.1	0.4	0.4	0.5
Total costs and expenses									1,856.5	1,613.3	1,513.6	477.7	290.5	268.2
Net income	$ 9.2	$ 31.8	$ 61.5	$ 119.6	$ 75.8	$ 93.1	$ 72.9	$ 53.2	$ 222.1	$ 295.0	$ 63.8										$ (1.4)	$ (2.1)	$ (3.6)