Long-Term Debt - Revolving Credit Facility - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2020 EUR (€)	Dec. 31, 2017 USD ($)
Line Of Credit Facility [Line Items]
Revolving credit facility, borrowings	$ 0
Kronos Worldwide, Inc. | Revolving North American Credit Facility
Line Of Credit Facility [Line Items]
Line of credit maximum borrowing capacity	$ 125,000,000
Fixed charge coverage ratio, minimum value	100.00%
Revolving credit facility, borrowings	$ 0	$ 0
Repayment of credit facility	$ 0	0
Kronos Worldwide, Inc. | Revolving North American Credit Facility | Maturity Date Option 1
Line Of Credit Facility [Line Items]
Line of credit, maturity month and year	2022-01
Kronos Worldwide, Inc. | Revolving North American Credit Facility | Minimum | Variable Rate
Line Of Credit Facility [Line Items]
Interest rate on outstanding borrowings	1.50%
Kronos Worldwide, Inc. | Revolving North American Credit Facility | Minimum | Base Rate Option
Line Of Credit Facility [Line Items]
Interest rate on outstanding borrowings	0.50%
Kronos Worldwide, Inc. | Revolving North American Credit Facility | Maximum | Variable Rate
Line Of Credit Facility [Line Items]
Interest rate on outstanding borrowings	2.00%
Kronos Worldwide, Inc. | Revolving North American Credit Facility | Maximum | Base Rate Option
Line Of Credit Facility [Line Items]
Interest rate on outstanding borrowings	1.00%
Kronos Worldwide, Inc. | North American Revolving Credit Facility
Line Of Credit Facility [Line Items]
Amount available for borrowing		107,600,000
Kronos Worldwide, Inc. | Letter Of Credit | Revolving North American Credit Facility
Line Of Credit Facility [Line Items]
Line of credit maximum borrowing capacity				$ 15,000,000
Kronos Worldwide, Inc. | Canadian Subsidiary Revolving Borrowings Maximum | Revolving North American Credit Facility
Line Of Credit Facility [Line Items]
Line of credit maximum borrowing capacity				$ 25,000,000
Kronos Worldwide, Inc. | European Revolving Credit Facility
Line Of Credit Facility [Line Items]
Line of credit maximum borrowing capacity | €			€ 90,000,000
Revolving credit facility, borrowings	$ 0	0
Repayment of credit facility	0	$ 0
Amount available for borrowing	$ 110,300,000		€ 90,000,000
Line of credit maturity month and year	2022-09
Outstanding borrowings under revolving credit facility	$ 0
Kronos Worldwide, Inc. | European Revolving Credit Facility | EURIBOR
Line Of Credit Facility [Line Items]
Interest rate on outstanding borrowings	1.60%