Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	FlexShares Trust
Prospectus Date	rr_ProspectusDate	Mar. 01, 2020
FlexShares Quality Dividend Defensive Index Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	FlexShares® Quality Dividend Defensive Index Fund
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund seeks investment results that correspond generally to the price and yield performance, before fees and expenses, of the Northern Trust Quality Dividend Defensive IndexSM (the “Underlying Index”).
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. Under the Fund’s Investment Advisory Agreement, the Fund is responsible for the following expenses: interest expenses, brokerage commissions and other trading expenses, fees and expenses of the independent trustees and their independent legal counsel, taxes and other extraordinary costs such as litigation and other expenses not incurred in the ordinary course of business. You will also incur usual and customary brokerage commissions when buying or selling shares of the Fund in the secondary market, which are not reflected in the example that follows:
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	March 1, 2021
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover.
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. Portfolio turnover may vary from year to year, as well as within a year. During the most recent fiscal year, the Fund’s portfolio turnover rate was 91% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	91.00%
Expense Exchange Traded Fund Commissions [Text]	rr_ExpenseExchangeTradedFundCommissions	You will also incur usual and customary brokerage commissions when buying or selling shares of the Fund in the secondary market, which are not reflected in the example that follows:
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same (taking into account the expense reimbursement arrangement for one year). Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Underlying Index is designed to reflect the performance of a selection of companies that, in aggregate, possess greater financial strength and stability characteristics relative to the Northern Trust 1250 Index (the “Parent Index”), a float-adjusted market-capitalization weighted index of U.S. domiciled large- and mid-capitalization companies. In addition, the Underlying Index is designed to select companies from the Parent Index that in the aggregate have the potential to generate income in excess of the income generated by securities in the Parent Index with a beta that is lower in relation to the Parent Index. Beta represents the market sensitivity, relative to a given market index and time period, and is one measure of volatility. To derive the Underlying Index, Northern Trust Investments, Inc. (“NTI” or the “Investment Adviser”), acting in its capacity as the index provider (the “Index Provider”), ranks all dividend-paying constituents of the Parent Index using a Northern Trust proprietary quality factor. This factor is a quantitative ranking based on: (a) management expertise (e.g. corporate finance activities); (b) profitability (e.g. reliability and sustainability of financial performance); and (c) cash flow (e.g., cash flow generation). The Index Provider then excludes the lowest quintile of constituents ranked according to this factor and uses an optimization process to select and weight eligible securities in order to (a) maximize the overall quality score relative to the Parent Index, (b) attain an aggregate dividend yield in excess of the Parent Index and (c) target an aggregate beta 0.5 to 1.0 times that of the Parent Index. The optimization also includes sector, industry group and single-security weight constraints so that these characteristics vary within acceptable bands relative to the Parent Index. In addition to tracking the performance of the Underlying Index, the Investment Adviser seeks to minimize portfolio turnover and tax inefficiencies. As of December 31, 2019, there were 161 issues in the Underlying Index. The Underlying Index is governed by transparent, objective rules for security selection, exclusion, rebalancing and adjustments for corporate actions. NTI uses a “passive” or indexing approach to try to achieve the Fund’s investment objective. Unlike many investment companies, the Fund does not try to “beat” its Underlying Index and does not seek temporary defensive positions when markets decline or appear overvalued. NTI uses a representative sampling strategy to manage the Fund. “Representative sampling” is investing in a representative sample of securities that collectively has an investment profile similar to the Underlying Index. The Fund may or may not hold all of the securities that are included in the Underlying Index. The Fund reserves the right to invest in substantially all of the securities in its Underlying Index in approximately the same proportions (i.e., replication) if NTI determines that it is in the best interest of the Fund. Under normal circumstances, the Fund will invest at least 80% of its total assets (exclusive of collateral held from securities lending) in the securities of the Underlying Index. The Fund may also invest up to 20% of its assets in cash and cash equivalents, including shares of money market funds advised by NTI or its affiliates, futures contracts and options on futures contracts, as well as securities not included in the Underlying Index, but which NTI believes will help the Fund track its Underlying Index. The Underlying Index is created and sponsored by NTI, as the Index Provider. NTI also serves as the investment adviser to the Fund. The Index Provider determines the composition and relative weightings of the securities in the Underlying Index and publishes information regarding the market value of the Underlying Index. The Index is reconstituted quarterly. The Fund may lend securities representing up to one-third of the value of the Fund’s total assets (including the value of the collateral received). Industry Concentration Policy. The Fund will concentrate its investments (i.e., hold 25% or more of its total assets) in a particular industry or group of industries to approximately the same extent that the Underlying Index is concentrated.
Strategy Portfolio Concentration [Text]	rr_StrategyPortfolioConcentration	Industry Concentration Policy. The Fund will concentrate its investments (i.e., hold 25% or more of its total assets) in a particular industry or group of industries to approximately the same extent that the Underlying Index is concentrated.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	As with any investment, you could lose all or part of your investment in the Fund, and the Fund’s performance could trail that of other investments. The Fund is subject to certain risks, including the principal risks noted below, any of which may adversely affect the Fund’s net asset value (“NAV”), trading price, yield, total return and ability to meet its investment objective. Each risk noted below is considered a principal risk of investing in the Fund, regardless of the order in which it appears. The significance of each risk factor below may change over time and you should review each risk factor carefully. Equity Securities Risk is the risk that the values of the equity securities owned by the Fund may be more volatile and underperform other asset classes and the general securities markets. Large Cap Risk is the risk that returns on investments in stocks of large companies could trail the returns on investments in stocks of smaller and mid-sized companies. U.S. Issuer Risk is the risk that certain changes in the U.S. economy, such as when the U.S. economy weakens or when its financial markets decline, may have an adverse effect on the securities to which the Fund has exposure. Information Technology Sector Risk is the risk that securities of technology companies may be subject to greater price volatility than securities of companies in other sectors. These securities may fall in and out of favor with investors rapidly, which may cause sudden selling and dramatically lower market prices. Technology securities also may be affected adversely by changes in technology, consumer and business purchasing patterns, government regulation and/or obsolete products or services. Technology companies may also be susceptible to heightened risk of cybersecurity breaches that may affect their security prices. Dividend Risk is the risk that an issuer of stock held by the Fund may choose not to declare a dividend or the dividend rate might not remain at current levels. Dividend paying stocks might not experience the same level of earnings growth or capital appreciation as non-dividend paying stocks. The Fund’s performance during a broad market advance could suffer because dividend paying stocks may not experience the same capital appreciation as non-dividend paying stocks. Volatility Risk is the risk that the actual level of volatility experienced by the Fund may be greater or lower than the targeted overall volatility of the Underlying Index. Although the Underlying Index is designed to have a targeted overall volatility that is lower than that of the Parent Index, there is no guarantee that it will have the targeted overall volatility. The Fund will continue to seek to track the Underlying Index even if the Underlying Index does not have the targeted overall volatility. There is also the risk that the Fund may experience volatility greater or lower than that of the Underlying Index as a result of tracking error. A portfolio of securities with greater volatility is generally considered to have a higher risk profile than a portfolio with lower volatility. Quality Factor Risk is the risk that the past performance of companies that have exhibited quality characteristics does not continue or the returns on securities issued by such companies may be less than returns from other styles of investing or the overall stock market. There may be periods when quality investing is out of favor and during which time the Fund's performance may suffer. Market Risk is the risk that the value of the Fund's investments may increase or decrease in response to expected, real or perceived economic, political or financial events in the U.S. or global markets. The frequency and magnitude of such changes in value cannot be predicted. Certain securities and other investments held by the Fund may experience increased volatility, illiquidity, or other potentially adverse effects in response to changing market conditions, inflation, changes in interest rates, lack of liquidity in the bond or equity markets, volatility in the equities market or adverse investor sentiment. Market risk includes the risk that a particular style of investing, such as growth or value, may underperform the market generally. The market value of the securities in which the Fund invests may go up or down in response to the prospects of individual companies, particular sectors or governments and/or general economic conditions throughout the world due to increasingly interconnected global economies and financial markets. Passive Investment Risk is the risk that the Fund is not actively managed and NTI does not attempt to take defensive positions in any market conditions, including declining markets. Tracking Error Risk is the risk that the Fund’s performance may vary substantially from the performance of the Underlying Index. The Fund’s performance may vary from the performance of the Underlying Index for a number of reasons including that the Fund incurs operating expenses that the Underlying Index does not. In addition, the Fund employs a representative sampling strategy, and therefore, may incur tracking error to a greater extent than a fund that seeks to replicate an index. The representative sampling strategy used by NTI may fail to produce the intended results. Authorized Participant Concentration Risk is the risk that the Fund may be adversely affected because it has a limited number of institutions that act as authorized participants (“Authorized Participants”). Only an Authorized Participant may engage in creation or redemption transactions directly with the Fund and none of those Authorized Participants is obligated to engage in creation and/or redemption transactions. To the extent that these institutions exit the business or are unable to proceed with creation and/or redemption orders with respect to the Fund and no other Authorized Participant is able to step forward to create or redeem Creation Units (as defined below), Fund shares may trade at a discount to NAV and possibly face trading halts and/or delisting. Calculation Methodology Risk is the risk that the Underlying Index’s calculation methodology or sources of information may not provide an accurate assessment of included issuers or correct valuation of securities, nor is the availability or timeliness of the production of the Index guaranteed. Market Trading Risk is the risk that the Fund faces because its shares are listed on a securities exchange, including the potential lack of an active market for Fund shares, losses from trading in secondary markets, periods of high volatility and disruption in the creation/redemption process of the Fund. ANY OF THESE FACTORS MAY LEAD TO THE FUND’S SHARES TRADING AT A PREMIUM OR DISCOUNT TO NAV. Trading in Fund shares may be halted due to market conditions or for reasons that, in the view of its listing exchange, make trading in the shares inadvisable. The market prices of Fund shares will generally fluctuate in accordance with changes in its NAV, changes in the relative supply of, and demand for, Fund shares, and changes in the liquidity, or the perceived liquidity, of the Fund’s holdings. Concentration Risk is the risk that, to the extent the Fund's investments are concentrated in the securities of issuers in a particular region, country, market, industry, sector or asset class, the Fund may be subject to increased price volatility and may be more susceptible to adverse economic, market, political or regulatory occurrences affecting that region, country, market, industry, sector or asset class. Cyber Security and Operational Risk is the risk that the Fund and its service providers may experience disruptions that arise from breaches in cyber security, human error, processing and communications errors, counterparty or third-party errors, technology or systems failures, any of which may have an adverse impact on the Fund. Failures or breaches of the electronic systems of the Fund, the Fund’s adviser, distributor, and other service providers, market makers, index providers, Authorized Participants or the issuers of securities in which the Fund invests have the ability to cause disruptions and negatively impact the Fund’s business operations, potentially resulting in financial losses to the Fund and its shareholders. The Fund and its investment adviser have limited ability to prevent or mitigate cybersecurity incidents affecting third-party service providers. Issuers of securities in which the Fund invests are also subject to cybersecurity risks, and the value of these securities could decline if the issuers experience cyber-attacks or other cyber-failures. Derivatives Risk is the risk that derivatives may pose risks in addition to and greater than those associated with investing directly in securities, currencies and other instruments, may be illiquid or less liquid, more volatile, more difficult to value and leveraged so that small changes in the value of the underlying instrument may produce disproportionate losses to the Fund. Derivatives are also subject to counterparty risk, which is the risk that the other party to the transaction will not perform its contractual obligations. Securities Lending Risk is the risk that the Fund may lose money because the borrower of the loaned securities fails to return the securities in a timely manner or at all. The Fund could also lose money in the event of a decline in the value of collateral provided for loaned securities or a decline in the value of any investments made with cash collateral. Valuation Risk is the risk that the sale price the Fund could receive for a portfolio security may differ from the Fund’s valuation of the security, particularly for securities that trade in low volume or volatile markets or that are valued using a fair value methodology. In addition, the value of the securities in the Fund’s portfolio may change on days when shareholders will not be able to purchase or sell the Fund’s shares. The Fund relies on various sources to calculate its NAV. The information may be provided by third parties that are believed to be reliable, but the information may not be accurate due to errors by such pricing sources, technological issues or otherwise. It is possible to lose money on an investment in the Fund. An investment in the Fund is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Risk Lose Money [Text]	rr_RiskLoseMoney	It is possible to lose money on an investment in the Fund.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Fund is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Fund Performance
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and table that follow show how the Fund has performed on a calendar year basis and provide an indication of the risks of investing in the Fund. Past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future. Updated information on the Fund’s performance results can be obtained by visiting www.flexshares.com.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and table that follow show how the Fund has performed on a calendar year basis and provide an indication of the risks of investing in the Fund.
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.flexshares.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	Past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Calendar Year Total Returns
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	For the periods in the bar chart above: Best Quarter (3/31/2019): 13.56% Worst Quarter (12/31/2018): -11.34%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (for the periods ended December 31, 2019)
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes.
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	After-tax returns shown are not relevant to investors who hold shares through tax-deferred arrangements, such as 401(k) plans or individual retirement plans.
Performance Table Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	After-tax returns may exceed the return before taxes due to an assumed tax benefit from realizing a capital loss on a sale of Fund shares.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold shares through tax-deferred arrangements, such as 401(k) plans or individual retirement plans. After-tax returns may exceed the return before taxes due to an assumed tax benefit from realizing a capital loss on a sale of Fund shares.
FlexShares Quality Dividend Defensive Index Fund | FlexShares Quality Dividend Defensive Index Fund
Risk/Return:	rr_RiskReturnAbstract
Management Fees	rr_ManagementFeesOverAssets	0.37%
Distribution (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.01%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.38%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.01%)	[1]
Total Annual Fund Operating Expenses After Expense Reimbursement	rr_NetExpensesOverAssets	0.37%
1 Year	rr_ExpenseExampleYear01	$ 38
3 Years	rr_ExpenseExampleYear03	121
5 Years	rr_ExpenseExampleYear05	212
10 Years	rr_ExpenseExampleYear10	$ 479
2013	rr_AnnualReturn2013	32.31%
2014	rr_AnnualReturn2014	13.43%
2015	rr_AnnualReturn2015	(0.21%)
2016	rr_AnnualReturn2016	15.39%
2017	rr_AnnualReturn2017	16.94%
2018	rr_AnnualReturn2018	(4.04%)
2019	rr_AnnualReturn2019	25.20%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2019
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	13.56%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2018
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(11.34%)
One Year	rr_AverageAnnualReturnYear01	25.20%
Five Year	rr_AverageAnnualReturnYear05	10.10%
Since Inception of Fund	rr_AverageAnnualReturnSinceInception	13.44%
Inception Date of Fund	rr_AverageAnnualReturnInceptionDate	Dec. 14, 2012
FlexShares Quality Dividend Defensive Index Fund | After Taxes on Distributions | FlexShares Quality Dividend Defensive Index Fund
Risk/Return:	rr_RiskReturnAbstract
One Year	rr_AverageAnnualReturnYear01	24.16%
Five Year	rr_AverageAnnualReturnYear05	9.02%
Since Inception of Fund	rr_AverageAnnualReturnSinceInception	12.44%
FlexShares Quality Dividend Defensive Index Fund | After Taxes on Distributions and Sale of Shares | FlexShares Quality Dividend Defensive Index Fund
Risk/Return:	rr_RiskReturnAbstract
One Year	rr_AverageAnnualReturnYear01	15.48%
Five Year	rr_AverageAnnualReturnYear05	7.74%
Since Inception of Fund	rr_AverageAnnualReturnSinceInception	10.73%
FlexShares Quality Dividend Defensive Index Fund | Russell 1000® Index
Risk/Return:	rr_RiskReturnAbstract
One Year	rr_AverageAnnualReturnYear01	31.43%	[2]
Five Year	rr_AverageAnnualReturnYear05	11.48%	[2]
Since Inception of Fund	rr_AverageAnnualReturnSinceInception	17.72%	[2]
FlexShares Quality Dividend Defensive Index Fund | Northern Trust Quality Dividend Defensive Index℠
Risk/Return:	rr_RiskReturnAbstract
One Year	rr_AverageAnnualReturnYear01	26.39%	[2]
Five Year	rr_AverageAnnualReturnYear05	10.91%	[2]
Since Inception of Fund	rr_AverageAnnualReturnSinceInception	14.11%	[2]

[1] Northern Trust Investments, Inc. (“NTI” or the “Adviser”) has contractually agreed to reimburse a portion of the operating expenses of the Fund (other than Acquired Fund Fees and Expenses) to the extent the “Total Annual Fund Operating Expenses” exceed 0.37%. This contractual limitation may not be terminated before March 1, 2021 without the approval of the Fund’s Board of Trustees. The Fund’s Board of Trustees may terminate the contractual agreement at any time if it determines that it is in the best interest of the Fund and its shareholders.

[2] Reflects no deduction for fees, expenses or taxes.