Related party transactions - Receivables from and Payables to Affiliates (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Current receivables from affiliates:
Contran income taxes	$ 1.9	$ 1.3
Current receivables from affiliates	3.1	0.8
Current payables to affiliates:
Other liabilities, primarily current	1.4	17.1
Payables to affiliate included in long-term debt:
Valhi - Contran credit facility	591.7	563.4
Long-term debt	590.9	484.4
Related Party
Current receivables from affiliates:
Current receivables from affiliates	3.1	0.8
Current payables to affiliates:
Other liabilities, primarily current	1.4	17.1
Payables to affiliate included in long-term debt:
Long-term debt	77.3	98.3
Contran
Current receivables from affiliates:
Contran income taxes	2.4
Contran trade items	0.1	0.2
Current payables to affiliates:
Contran income taxes		16.9
Contran trade items	1.3	0.2
VALHI, INC. | Contran | Line of Credit [Member]
Payables to affiliate included in long-term debt:
Valhi - Contran credit facility	23.6	44.6
Kronos | Contran | Term loan
Payables to affiliate included in long-term debt:
Kronos - Contran Term Loan	53.7	53.7
Other Affiliates [Member]
Current receivables from affiliates:
Current receivables from affiliates	0.6	$ 0.6
Current payables to affiliates:
Other liabilities, primarily current	$ 0.1