Valhi Stockholders' Equity - Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income Loss [Line Items]
Marketable securities, Balance at beginning of year	$ 2.8	$ 2.1	$ 6.4
Marketable securities, Unrealized gain (loss) arising during the year	(1.0)		4.1
Reclassification adjustments for amounts included in realized gain (loss)	(0.2)	0.7	(8.4)
Marketable securities, Balance at end of year	1.6	2.8	2.1
Currency translation, Balance at beginning of year	59.2	53.3	37.5
Currency translation, Arising during the year	(81.8)	5.9	23.0
Reclassification adjustments for amounts included in gain on disposal			(7.2)
Currency translation, Balance at end of year	(22.6)	59.2	53.3
Balance at beginning of year	(8.0)	(42.0)	(23.3)
Other comprehensive income (loss)	(140.6)	34.0	(18.7)
Balance at end of year	(148.6)	(8.0)	(42.0)
Pension Plan Defined Benefit
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of year	(76.5)	(101.5)	(72.6)
Amortization of prior service cost and net losses included in net periodic pension cost	6.3	8.4	6.1
Net actuarial gain (loss) arising during year	(61.7)	12.6	(35.0)
Plan curtailment	(0.1)	4.0
Balance at end of year	(132.0)	(76.5)	(101.5)
OPEB
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of year	6.5	4.1	5.4
Amortization of prior service cost and net losses included in net periodic pension cost	(1.3)	(1.4)	(1.0)
Net actuarial gain (loss) arising during year	(0.8)	1.3	(0.3)
Plan amendment		2.5
Balance at end of year	$ 4.4	$ 6.5	$ 4.1

Accumulated appreciation or loss, net of tax, in value of the total of available-for-sale securities at the end of an accounting period.

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Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains or losses.

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount after tax of (increase) decrease in the value of the projected benefit obligation related to a change in an actuarial assumption and increase (decrease) in the value of the plan assets resulting from experience different from that assumed, that has not been recognized in net periodic benefit (cost) credit.

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Amount after tax, before reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount after tax of reclassification adjustment from accumulated other comprehensive income for translation gain (loss) realized upon the sale or liquidation of an investment in a foreign entity and foreign currency hedges that are designated and qualified as hedging instruments for hedges of the foreign currency exposure of a net investment in a foreign operation.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount after tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

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Amount after tax of reclassification adjustment from accumulated other comprehensive (income) loss for net gain (loss) and prior service cost (credit) related to pension and other postretirement benefit plans.

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Amount after tax of reclassification adjustment from accumulated other comprehensive income (loss) for plan amendment related to pension and other postretirement benefit plans.

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Amount after tax of reclassification adjustment from accumulated other comprehensive income (loss) for plan curtailments related to pension and other postretirement benefit plans.

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