Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	FlexShares Trust
Prospectus Date	rr_ProspectusDate	Mar. 01, 2020
FlexShares Credit-Scored US Long Corporate Bond Index Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	FlexShares® Credit-Scored US Long Corporate Bond 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 US Long Corporate Bond Quality Value 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 other 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 44% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	44.00%
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 reflects the performance of a broad universe of US-dollar denominated investment grade corporate bonds that can potentially deliver a higher total return than the overall investment grade corporate bond market, as represented by the Northern Trust US Investment Grade Long Corporate Bond IndexSM (the “Parent Index”). The securities included in the Underlying Index are a subset of the securities included in the Parent Index, a market capitalization-weighted index comprised of US dollar-denominated investment grade bonds. The Fund may invest in U.S. dollar denominated bonds of non-U.S. corporations to the extent such bonds are included in the Underlying Index. Such investment will not exceed 20% of the net assets of the Fund. The Underlying Index begins with the Parent Index and then follows a rules-based methodology to select and weight securities, subject to certain constraints as described below, to optimize the Underlying Index’s exposure to a combined proprietary value score and a proprietary quality score, as determined by NTI acting in its capacity as index provider (“Index Provider”). The Value score is a quantitative measure of the relative attractiveness of each security’s valuation compared to its market price or relative valuation versus other similar securities, and is computed based on market and fundamental measures, including issuer default risk. The quality score is a quantitative ranking, based on: (a) an assessment of management efficiency (e.g. corporate finance activities); (b) profitability (reliability and sustainability of financial performance); and (c) financial solvency (e.g. debt servicing capacity). Utilizing the value and quality scores, the index methodology seeks to identify bonds that are trading at market prices that are lower relative to levels implied by their fundamentals, thus creating a potential opportunity for capital appreciation and higher income compared to the broader investment grade corporate bond market. In addition, at the time of index reconstitution, the weighting of the Underlying Index’s constituent securities will be adjusted such that the effective duration and the sector exposures of the Underlying Index are similar to those of the Parent Index. Issuer and issue exposures are constrained to manage concentration risk. In order to be eligible for inclusion in the Parent and Underlying Indexes, a security must be a fixed rate taxable bond that is either publicly offered in the U.S. or that is offered pursuant to Rule 144A under the Securities Act of 1933, as amended (the “Securities Act”), with registration rights. A security also must be rated, at the time of inclusion in the Parent and Underlying Index, within the top four rating categories by a Nationally Recognized Statistical Rating Organization (“NRSRO”). In addition, an eligible bond must have (a) a final time to stated maturity that is greater than or equal to 10 years and (b) at least $250 million in outstanding principal. As of January 31, 2020, there were 943 issues in the Underlying Index. The Underlying Index is a new index with an inception date of January 31, 2020. 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” the index it tracks and does not seek temporary defensive positions when markets decline or appear overvalued. In addition to tracking the performance of the Underlying Index, the Investment Adviser seeks to minimize portfolio turnover and tax inefficiencies. NTI uses 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. The Fund generally will invest under normal circumstances at least 80% of its total assets (exclusive of collateral held from securities lending) in the securities of its 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, 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 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). The Fund is “non-diversified” under the Investment Company Act of 1940 (“1940 Act”), as amended, and may invest more of its assets in fewer issuers than “diversified” funds. 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. Corporate Bond Risk is the risk the Fund faces because it invests primarily in bonds issued by corporations. Corporate debt securities are subject to the risk of the issuer’s inability to meet principal and interest payments on the obligation and may also be subject to price volatility due to such factors as interest rate sensitivity, market perception of the creditworthiness of the issuer and general market liquidity. When interest rates rise, the value of corporate debt can be expected to decline. Debt securities with longer maturities tend to be more sensitive to interest rate movements than those with shorter maturities. Quality-Value Score Risk is the risk that the Fund’s investment in companies whose securities are believed to be undervalued will not appreciate in value as anticipated or the past performance of companies that have exhibited quality characteristics does not continue. Although the Underlying Index is designed to measure a portfolio of bonds that can potentially deliver a higher total return relative to the Parent Index, there is no assurance that the Underlying Index or Fund will be comprised of such securities. Accordingly, the Fund may be subject to greater credit risk, price volatility and risk of loss relative to the Parent Index. Income Risk is the risk that the Fund’s income may decline when interest rates fall. This decline can occur because the Fund must invest in lower-yielding bonds as bonds in its portfolio mature, bonds in the Underlying Index are substituted or the Fund otherwise needs to purchase additional bonds. 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. 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. The Underlying Index is a new index with an inception date of January 31, 2020. 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. Credit (or Default) Risk is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a TBA, repurchase or other transaction, to meet its payment or other financial obligations will adversely affect the value of the Fund’s investments and its returns. Changes in a debt security’s or an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also adversely affect the value of the Fund’s investment in that issuer. Although the Underlying Index is designed to measure a portfolio of bonds of companies with higher credit quality and low risk of default relative to the Parent Index, there is no assurance that the Underlying Index or Fund will be comprised of such securities or that companies that have historically exhibited fundamentals consistent with high credit quality will continue to exhibit such fundamentals. The degree of credit risk depends on the issuer’s or counterparty’s financial condition and on the terms of the securities. 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. Debt Extension Risk is the risk that an issuer will exercise its right to pay principal on an obligation held by the Fund later than expected. This may happen during a period of rising interest rates. Under these circumstances, the value of the obligation will decrease and the Fund will suffer from the inability to invest in higher yielding securities. 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. Financial Sector Risk is the risk that the Fund will be impacted by events affecting the financial sector if it invests a relatively large percentage of its assets in that sector, adversely affecting the Fund’s performance. The financial sector can be significantly affected by changes in interest rates, government regulation, the rate of corporate and consumer debt defaulted, price competitions and the availability and cost of capital funds, among other factors. High Portfolio Turnover Risk is the risk that active and frequent trading of the Fund’s portfolio securities may result in increased transaction costs to the Fund, including brokerage commissions, dealer mark-ups and other transaction costs, which could reduce the Fund’s return. Interest Rate/Maturity Risk is the risk that the value of the Fund’s fixed-income assets will decline because of rising interest rates. The magnitude of this decline will often be greater for longer-term fixed-income securities than shorter-term fixed-income securities. Duration is a measure used to determine the sensitivity of a security’s price to changes in interest rates. The longer a security’s duration, the more sensitive it will be to changes in interest rates. The Fund currently faces a heightened level of interest rate risk because interest rates are at historically low levels, but are expected to increase in the future with unpredictable effects on the markets and the Fund’s investments. An increase in interest rates may cause investors to move out of fixed incomes securities on a large scale, which could adversely affect the price of fixed income securities, lead to heightened volatility in the fixed-income markets and may adversely affect the liquidity of certain fixed-income investments. Liquidity Risk is the risk that certain portfolio securities may be less liquid than others, which may make them difficult or impossible to sell at the time and the price that the Fund would like, adversely affecting the value of the Fund’s investments and its returns. Illiquid investments may be harder to value, especially in changing markets, and if the Fund is forced to sell these investments to meet redemption requests or for other cash needs, the Fund may suffer a loss. Liquidity Risk may result from the lack of an active market, reduced number and capacity of traditional market participants to make a market in fixed income securities, and may be magnified in a rising interest rate environment or other circumstances where investor redemptions from fixed income funds may be higher than normal, causing increased supply in the market due to selling activity. The market for certain investments may become illiquid under adverse market or economic conditions independent of any specific adverse changes in the conditions of a particular issuer. In such cases, the Fund, due to limitations on investments in illiquid securities and/or purchasing and selling such investments, may be unable to achieve a high degree of correlation with the Underlying Index. Additionally, in adverse market conditions, the Fund’s market price may begin to reflect illiquidity or pricing uncertainty of the Fund’s portfolio securities. This could lead to the Fund’s shares trading at a price that is higher or lower than the Fund’s net asset value. At times, such differences may be significant. Non-Diversification Risk is the risk that Fund performance may depend on the performance of a small number of issuers because the Fund may invest a large percentage of its assets in securities issued by or representing a small number of issuers. Non-U.S. Issuer Risk is the risk the Fund faces because it may invest in U.S. dollar denominated bonds of non-U.S. corporations to the extent such bonds are included in the Underlying Index. The Fund’s investments in bonds of non-U.S. issuers may involve certain risks that are greater than those associated with investments in securities of U.S. issuers. These include the risks of adverse economic, political, diplomatic, financial and regulatory conditions that may affect non-U.S. issuers. Prepayment (or Call) Risk is the risk that an issuer of a security held by the Fund may “call” or prepay the security before its stated maturity, during periods of falling interest rates, e.g., which may result in the Fund having to invest the proceeds at lower interest rates, resulting in a decline in the Fund’s income and accordingly, a decline in the Fund’s net asset value. Issuers may be more likely to prepay their securities if interest rates fall. If this happens, the Fund will not benefit from the rise in the market price of the securities that normally accompanies a decline in interest rates, and will be forced to reinvest prepayment proceeds at a time when yield on securities available in the market are lower than the yield on prepaid securities. The Fund may also lose any premium it paid to purchase the securities. 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.
Risk Nondiversified Status [Text]	rr_RiskNondiversifiedStatus	Non-Diversification Risk is the risk that Fund performance may depend on the performance of a small number of issuers because the Fund may invest a large percentage of its assets in securities issued by or representing a small number of issuers.
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): 8.14% Worst Quarter (12/31/2016): -5.56%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (for the periods ended December 31, 2019)
Performance Table Market Index Changed	rr_PerformanceTableMarketIndexChanged	Until March 16, 2020, the Fund's underlying index is the Northern Trust Credit-Scored US Long Corporate Bond IndexSM. Beginning March 16, 2020, the underlying index is the Northern Trust US Long Corporate Bond Quality Value IndexSM. Performance information for the Northern Trust US Long Corporate Bond Quality Value IndexSM is not available for periods prior to its commencement date of January 31, 2020.
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. * Effective March 16, 2020, the Fund's principal investment strategies are revised.
FlexShares Credit-Scored US Long Corporate Bond Index Fund | FlexShares Credit-Scored US Long Corporate Bond Index Fund
Risk/Return:	rr_RiskReturnAbstract
Management Fees	rr_ManagementFeesOverAssets	0.22%
Distribution (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.01%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.23%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.01%)	[1]
Total Annual Fund Operating Expenses After Expense Reimbursement	rr_NetExpensesOverAssets	0.22%
1 Year	rr_ExpenseExampleYear01	$ 23
3 Years	rr_ExpenseExampleYear03	73
5 Years	rr_ExpenseExampleYear05	129
10 Years	rr_ExpenseExampleYear10	$ 292
2016	rr_AnnualReturn2016	9.95%
2017	rr_AnnualReturn2017	12.03%
2018	rr_AnnualReturn2018	(7.92%)
2019	rr_AnnualReturn2019	24.23%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2019
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	8.14%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2016
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(5.56%)
One Year	rr_AverageAnnualReturnYear01	24.23%
Since Inception of Fund	rr_AverageAnnualReturnSinceInception	8.03%
Inception Date of Fund	rr_AverageAnnualReturnInceptionDate	Sep. 23, 2015
FlexShares Credit-Scored US Long Corporate Bond Index Fund | After Taxes on Distributions | FlexShares Credit-Scored US Long Corporate Bond Index Fund
Risk/Return:	rr_RiskReturnAbstract
One Year	rr_AverageAnnualReturnYear01	22.25%
Since Inception of Fund	rr_AverageAnnualReturnSinceInception	6.07%
FlexShares Credit-Scored US Long Corporate Bond Index Fund | After Taxes on Distributions and Sale of Shares | FlexShares Credit-Scored US Long Corporate Bond Index Fund
Risk/Return:	rr_RiskReturnAbstract
One Year	rr_AverageAnnualReturnYear01	14.25%
Since Inception of Fund	rr_AverageAnnualReturnSinceInception	5.28%
FlexShares Credit-Scored US Long Corporate Bond Index Fund | Bloomberg Barclays Long U.S. Corporate Bond Index
Risk/Return:	rr_RiskReturnAbstract
One Year	rr_AverageAnnualReturnYear01	23.89%	[2]
Since Inception of Fund	rr_AverageAnnualReturnSinceInception	8.39%	[2]
FlexShares Credit-Scored US Long Corporate Bond Index Fund | Northern Trust Credit-Scored US Long Corporate Bond Index℠
Risk/Return:	rr_RiskReturnAbstract
One Year	rr_AverageAnnualReturnYear01	25.07%	[2],[3]
Since Inception of Fund	rr_AverageAnnualReturnSinceInception	8.57%	[2],[3]
FlexShares Credit-Scored US Long Corporate Bond Index Fund | Northern Trust US Long Corporate Bond Quality Value Index℠
Risk/Return:	rr_RiskReturnAbstract
One Year	rr_AverageAnnualReturnYear01		[2],[3]
Since Inception of Fund	rr_AverageAnnualReturnSinceInception		[2],[3]

[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 0.22%. 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.

[3] Until March 16, 2020, the Fund’s underlying index is the Northern Trust Credit-Scored US Long Corporate Bond Index℠. Beginning March 16, 2020, the underlying index is the Northern Trust US Long Corporate Bond Quality Value Index℠. Performance information for the Northern Trust US Long Corporate Bond Quality Value Index℠ is not available for periods prior to its commencement date of January 31, 2020.