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Investment in Kronos Worldwide, Inc. - Selected Financial Information of Kronos Income Statement (Detail) (Kronos, USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Kronos
    
Schedule Of Equity Method Investments [Line Items]    
Net sales $ 365.1us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= nl_KronosWorldwideIncMember		 $ 420.1us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= nl_KronosWorldwideIncMember
Cost of sales 287.7us-gaap_EquityMethodInvestmentSummarizedFinancialInformationCostOfSales
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= nl_KronosWorldwideIncMember		 339.6us-gaap_EquityMethodInvestmentSummarizedFinancialInformationCostOfSales
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= nl_KronosWorldwideIncMember
Income from operations 32.2us-gaap_EquityMethodInvestmentSummarizedFinancialInformationGrossProfitLoss
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= nl_KronosWorldwideIncMember		 26.0us-gaap_EquityMethodInvestmentSummarizedFinancialInformationGrossProfitLoss
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= nl_KronosWorldwideIncMember
Net income $ 18.4us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= nl_KronosWorldwideIncMember		 $ 14.3us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= nl_KronosWorldwideIncMember