TiO2 segment information - Reconciliation of segment profit (loss) and Consolidated net income (loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Geographic Information [Line Items]
Net sales	$ 489.8	$ 478.8
Segment profit	25.7	11.6
Corporate interest and dividend income	0.4	1.3
Marketable equity securities	1.0	(0.3)
Other components of net periodic pension and OPEB cost	(0.5)	(0.3)
Interest expense	(11.6)	(9.2)
Income tax expense	(7.6)	(3.5)
Net income	18.1	8.1
Corporate non segment
Geographic Information [Line Items]
Corporate expenses	(3.0)	(3.5)
Corporate interest and dividend income	0.2	0.9
Single reportable segment | Operating segment
Geographic Information [Line Items]
Net sales	489.8	478.8
Segment profit	41.6	23.4
Marketable equity securities	(1.0)	0.3
Other components of net periodic pension and OPEB cost	(0.5)	(0.3)
Interest expense	(11.6)	(9.2)
Income tax expense	$ (7.6)	$ (3.5)