Financial instruments and fair value measurements - Financial Instruments not Carried at Fair Value (Detail) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash equivalents, Fair value	$ 207,500,000	$ 395,900,000
Cash, cash equivalents and restricted cash equivalents	207,500,000	395,900,000
Noncontrolling interest, Carrying amount	345,700,000	358,100,000
Valhi stockholders' equity, Carrying amount	656,900,000	733,600,000
Kronos Worldwide, Inc. [Member] | Common stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Noncontrolling interest	355,200,000	442,600,000
Noncontrolling interest, Carrying amount	251,200,000	267,000,000
Kronos Worldwide, Inc. [Member] | Note Payable [Member] | Contran [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value	185,000,000
Long term debt - Kronos note payable to Contran	185,000,000
Kronos Worldwide, Inc. [Member] | Term Loan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value	101,600,000	396,800,000
Loans, Carrying amount	98,600,000	384,500,000
Kronos Worldwide, Inc. [Member] | Bank Credit Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Variable rate bank credit facility, Fair value	12,800,000	13,200,000
Variable rate bank credit facility, Carrying amount	12,800,000	13,200,000
Snake River [Member] | Fixed Rate Loans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value	250,000,000	250,000,000
Loans, Carrying amount	250,000,000	250,000,000
WCS [Member] | Fixed Rate Loans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value	76,800,000	77,100,000
Loans, Carrying amount	76,800,000	77,100,000
Valhi [Member] | Credit Facility [Member] | Contran [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Variable rate bank credit facility, Fair value	149,000,000	157,600,000
Variable rate bank credit facility, Carrying amount	149,000,000	157,600,000
CompX [Member] | Common stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Noncontrolling interest	20,700,000	23,400,000
Noncontrolling interest, Carrying amount	13,200,000	13,300,000
CompX [Member] | Promissory Note [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, fair value	18,200,000	18,500,000
Variable rate promissory note, Carrying amount	18,200,000	18,500,000
NL [Member] | Common stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Noncontrolling interest	102,900,000	94,800,000
Noncontrolling interest, Carrying amount	81,300,000	77,800,000
Valhi Inc [Member] | Stockholders' Equity, Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Valhi stockholders' equity, Fair value	5,442,800,000	4,238,900,000
Valhi stockholders' equity, Carrying amount	$ 656,900,000	$ 733,600,000