Business segment information - Additional Information (Detail) In Millions, unless otherwise specified	Mar. 31, 2013
Kronos Worldwide, Inc. [Member]
Segment Reporting Information [Line Items]
Direct controlling interest in subsidiary	50.00%
Indirect controlling interest in subsidiary	30.00%
Total controlling interest	80.00%
Kronos Worldwide, Inc. [Member] | Contran [Member]
Segment Reporting Information [Line Items]
Common stock pledged as collateral	12.0
NL [Member]
Segment Reporting Information [Line Items]
Total controlling interest	83.00%