Fair Value Measurements and Financial Instruments - Financial Instruments not Carried at Fair Value (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Noncontrolling interest in subsidiaries	$ 323.0us-gaap_MinorityInterest	$ 336.3us-gaap_MinorityInterest
Valhi stockholders' equity	432.2us-gaap_StockholdersEquity	477.6us-gaap_StockholdersEquity
Kronos Worldwide, Inc.
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Noncontrolling interest in subsidiaries	198.3	211.0
Kronos Worldwide, Inc. \| Term Loan
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	345.1	345.9
Long term debt, fair value	350.8	341.5
Snake River \| Term Loan
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	250.0	250.0
Long term debt, fair value	250.0	250.0
WCS \| Fixed Rate Loans
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	66.8	67.1
Long term debt, fair value	66.8	67.1
VALHI, INC. \| Credit Facility \| Contran
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	229.2	223.7
Long term debt, fair value	229.2	223.7
Tremont \| Promissory Note
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	17.3	17.4
Long term debt, fair value	17.3	17.4
BMI \| Bank note payable
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	10.1	10.3
Long term debt, fair value	10.1	10.3
LandWell
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Noncontrolling interest in subsidiaries	24.5	24.8
LandWell \| Unsecured Debt
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	3.1	3.1
Long term debt, fair value	3.1	3.1
NL
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Noncontrolling interest in subsidiaries	53.7	54.4
CompX
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Noncontrolling interest in subsidiaries	14.7	14.4
Reported Value Measurement
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash equivalents	224.1	280.3
Deferred payment obligation	8.6	8.5
Valhi stockholders' equity	432.2	477.6
Reported Value Measurement \| Kronos Worldwide, Inc.
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Noncontrolling interest in subsidiaries	198.3	211.0
Reported Value Measurement \| NL
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Noncontrolling interest in subsidiaries	53.7	54.4
Reported Value Measurement \| CompX
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Noncontrolling interest in subsidiaries	14.7	14.4
Portion at Fair Value Measurement
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash equivalents	224.1	280.3
Deferred payment obligation	8.6	8.5
Valhi stockholders' equity	2,112.8	2,173.8
Portion at Fair Value Measurement \| Kronos Worldwide, Inc.
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Noncontrolling interest in subsidiaries	286.7	295.1
Portion at Fair Value Measurement \| NL
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Noncontrolling interest in subsidiaries	64.3	71.3
Portion at Fair Value Measurement \| CompX
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Noncontrolling interest in subsidiaries	$ 18.7	$ 19.9

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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-Publisher SEC

-Name Regulation S-X (SX)

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which is directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent (that is, noncontrolling interest, previously referred to as minority interest).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

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-Paragraph 1

-Subparagraph (SX 210.5-02.31)

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- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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- Definition

The fair value of cash and cash equivalent items, current restricted cash and equivalent items and noncurrent restricted cash and equivalent items. This element is for unclassified presentations, so both current and noncurrent components are included.

+ References

No definition available.

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- Definition

Deferred payment obligation fair value disclosure.

+ References

No definition available.

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