Amount of net assets (liabilities).

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Name:	us-gaap_AssetsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Business and Geographic Segments - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) Segment	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments \| Segment	3
Non-U.S. subsidiaries
Segment Reporting Information [Line Items]
Net assets of non-U.S. subsidiaries \| $	$ 565	$ 563
Kronos Worldwide, Inc. \| Valhi Incorporation
Segment Reporting Information [Line Items]
Direct ownership percentage by parent	50.00%
Kronos Worldwide, Inc. \| NL
Segment Reporting Information [Line Items]
Indirect controlling interest in subsidiary	30.00%
NL \| Valhi Incorporation
Segment Reporting Information [Line Items]
Direct ownership percentage by parent	83.00%
LandWell \| Valhi Incorporation
Segment Reporting Information [Line Items]
Direct ownership percentage by parent	27.00%
LandWell \| BMI
Segment Reporting Information [Line Items]
Indirect controlling interest in subsidiary	50.00%
BMI \| Valhi Incorporation
Segment Reporting Information [Line Items]
Direct ownership percentage by parent	63.00%