| Label | Element | Value | ||||||
|---|---|---|---|---|---|---|---|---|
| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk/Return [Heading] | rr_RiskReturnHeading | FlexShares® ESG & Climate Investment Grade Corporate Core 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 ESG & Climate Investment Grade U.S. Corporate Core IndexSM (the “Underlying Index”).
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| 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, hold and sell 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 and fees to financial intermediaries when buying or selling shares of the Fund in the secondary market, which are not reflected in the example that follows:
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| Operating Expenses Caption [Text] | rr_OperatingExpensesCaption | Annual Fund Operating Expenses (expenses that you pay eachyear as a percentage of the value of your investment) | ||||||
| Fee Waiver or Reimbursement over Assets, Date of Termination | rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination | March 1, 2026 | ||||||
| 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 41% of the average value of its portfolio. | ||||||
| Portfolio Turnover, Rate | rr_PortfolioTurnoverRate | 41.00% | ||||||
| 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 sell 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:
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| Strategy [Heading] | rr_StrategyHeading | Principal Investment Strategies | ||||||
| Strategy Narrative [Text Block] | rr_StrategyNarrativeTextBlock | The Underlying Index, administered by NTI in its capacity as index provider (the “Index Provider”), is designed to reflect the performance of a selection of U.S.-dollar-denominated corporate bonds issued by companies that exhibit certain environmental, social and governance (“ESG”) characteristics in the aggregate, while also seeking to provide exposure to US dollar-denominated corporate bonds, i.e., the constituents in the Northern Trust Investment Grade U.S. Corporate Bond IndexSM (the “Eligible Universe”). The Northern Trust Investment Grade U.S. Corporate Bond IndexSM is a market-capitalization weighted index comprised of US dollar-denominated corporate bonds that (a) are publicly issued in the United States and registered with the SEC or eligible for resale under Rule 144A under the Securities Act of 1933, with or without registration rights, (b) are rated investment grade (i.e., rated at the time of inclusion in the Eligible Universe within the top four ratings categories by a Nationally Recognized Statistical Rating Organization (“NRSRO”)), and (c) have, at each rebalance, (i) a final time to stated maturity of at least one year and (ii) an outstanding principal balance of at least $250 million. The Fund does not have any portfolio maturity limitation and may invest its assets from time to time in instruments with varying maturities. The Underlying Index starts by excluding certain companies from the Eligible Universe that, based on third-party data, are determined to have certain levels of controversial business involvement or behavior, including in tobacco, weaponry, thermal coal, unconventional oil and gas, and for-profit prisons, or to have caused, contributed to or are linked to certain violations of international norms and standards. Such exclusions are based on percentage of revenue thresholds for certain categories (e.g., those that receive significant revenue from production, retail and distribution of civilian weapons) and categorical exclusions for others (e.g., tobacco producers). The above-described exclusionary screens are applied with each reconstitution of the Underlying Index. The Index Provider may modify this list of excluded companies at any time, at its own discretion. The Underlying Index next applies an optimization process to minimize variance to the Eligible Universe while also targeting certain ESG characteristics, which is designed to produce an index that, relative to the Eligible Universe: (a) has an aggregate higher scoring of certain ESG characteristics, as measured by the Northern Trust ESG Vector Score (“ESG Vector Score”) described below, (b) improves the carbon risk rating, as measured by certain carbon-related risk metrics, and (c) decreases the weighted average carbon intensity and potential emissions. The ESG Vector Score is designed to rank companies based on their management of and exposure to material ESG metrics as defined by the Sustainability Accounting Standards Board (“SASB”) Standards. In addition, the Index Provider uses available data from Institutional Shareholder Services ESG Solutions to assess carbon emissions intensity, carbon reserves and a carbon risk rating. Carbon emissions intensity measures (i) direct greenhouse gas emissions from sources controlled or owned by the company (e.g., emissions associated with fuel combustion in boilers, furnaces, or vehicles); and (ii) indirect greenhouse gas emissions associated with the purchase of electricity, steam, heat or cooling against the company. Carbon reserves measure the total estimated greenhouse gas emissions attributable to a company’s fossil fuel reserve assets. The carbon risk rating provides an assessment of a company’s ability to mitigate the risks of transition to a lower carbon economy based on its specific baseline carbon risk exposure. In the event that metrics or other data used to construct the ESG Vector Score as well as carbon emissions intensity, carbon reserves and/or the carbon risk rating are not available or otherwise deemed unreliable, NTI may make reasonable estimates or otherwise exercise its discretion to implement the optimization process. Notwithstanding the optimization process, it is possible that the Underlying Index will include (and therefore the Fund could invest in) securities that, individually, have a lower ESG Vector Score, lower carbon risk rating, or higher emissions relative to the weighted average of the Eligible Universe. The optimization process also includes sector, country, turnover, issuer and constituent constraints so that these characteristics in the Underlying Index vary within acceptable bands relative to the Eligible Universe. The Underlying Index is a new index with an inception date of July 30, 2021. As of December 31, 2024, there were 3698 issues in the Underlying Index. The Underlying Index is reconstituted monthly under normal market conditions. The Fund generally reconstitutes its portfolio in accordance with the Underlying Index. 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. 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, to-be-announced (“TBA”) transactions, 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). 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. As of December 31, 2024, the Underlying Index was concentrated in the financial sector. The components of the Underlying Index, and the degree to which these components represent certain industries or sectors, may change over time.
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| 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. As of December 31, 2024, the Underlying Index was concentrated in the financial sector. The components of the Underlying Index, and the degree to which these components represent certain industries or sectors, may change over time. | ||||||
| Risk [Heading] | rr_RiskHeading | Principal Risks | ||||||
| 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 by showing (A) changes in the Fund’s performance from year to year, (B) how the Fund’s average annual returns compare with those of a broad measure of market performance, and (C) an additional index with characteristics relevant to 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 flexshares.com.
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| 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 by showing (A) changes in the Fund’s performance from year to year, (B) how the Fund’s average annual returns compare with those of a broad measure of market performance, and (C) an additional index with characteristics relevant to the Fund. | ||||||
| Performance Availability Website Address [Text] | rr_PerformanceAvailabilityWebSiteAddress | 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 shown in the bar chart above: Best Quarter (12/31/2023): 8.32% Worst Quarter (3/31/2022): -7.45%
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| Performance Table Heading | rr_PerformanceTableHeading | Average Annual Total Returns (for the periods ended December 31, 2024) | ||||||
| Performance Table Market Index Changed | rr_PerformanceTableMarketIndexChanged | In connection with new regulatory requirements, the Fund has changed its broad-based securities market benchmark from the Bloomberg US Corporate Total Return Value Unhedged Index to the Bloomberg U.S. Aggregate Bond Index. The Fund will continue to compare its performance to the Bloomberg US Corporate Total Return Value Unhedged Index, which reflects the market segments in which the Fund invests. | ||||||
| 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-advantaged 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 beforetaxes 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-advantaged 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.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Risk Lose Money [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | It is possible to lose money on an investment in the Fund. | ||||||
| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Risk Not Insured Depository Institution [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | 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. | ||||||
| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | ESG Investment Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | ESG Investment Risk is the risk that because the Index Provider includes and excludes issuers and assigns weights to issuers in the Underlying Index by applying non-financial factors, the Fund may underperform the broader equity market or other funds that do or do not use ESG factors, scores, or screens in their securities selection process, or use a different ESG methodology. The ESG methodology of the Underlying Index will affect the Fund’s exposure to certain companies and sectors and may adversely affect the Fund’s performance depending on whether such companies and sectors are in or out of favor. Although the Underlying Index is designed to measure a portfolio of companies with certain ESG characteristics, there is no assurance that every security in the Underlying Index or Fund will have ESG characteristics or that companies that have historically exhibited such characteristics will continue to exhibit such characteristics. There is also the risk that the Fund may have indirect exposure to companies that have been excluded from the Underlying Index through its use of certain derivative instruments. Currently, there is a lack of common industry standards relating to the development and application of ESG criteria, which may make it difficult to compare the Fund’s principal investment strategies with the investment strategies of other funds that integrate certain ESG criteria. The subjective value that investors may assign to certain types of ESG characteristics may differ substantially from that of the assessment by the Index Provider or a data provider. Investors can differ in their views of what constitutes positive or negative ESG characteristics. As a result, the Fund may invest in companies that do not reflect the beliefs and values of any particular investor. A company included in the Underlying Index may not exhibit positive or favorable ESG characteristics. The companies selected by the Index Provider as demonstrating certain ESG characteristics may not be the same companies selected by other index providers or investment managers as exhibiting those characteristics. The Index Provider relies on various sources of information regarding an issuer, including information that may be based on assumptions and estimates. ESG information from third-party data providers may be incomplete, inaccurate or unavailable. Neither the Fund nor NTI can offer assurances that the Underlying Index’s methodology or sources of information will provide an accurate assessment of the issuers of the securities included in the Fund’s Underlying Index. The Index Provider uses third-party data that it believes to be reliable, but it does not guarantee the accuracy of such third-party data. Data can vary across providers or within industries. ESG standards differ by region and industry, and a company’s ESG practices or the Index Provider’s or data providers’ assessment of a company’s ESG practices may change over time. Regulatory changes or interpretations regarding the definitions and/or use of ESG criteria could have a material adverse effect on the Fund’s ability to invest in accordance with its investment policies and/or achieve its investment objective.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Corporate Bond Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | 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.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Credit or Default Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | 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. The credit quality of a debt security or of the issuer of a debt security held by the Fund could deteriorate rapidly, which may impair the Fund’s liquidity or cause a deterioration in the Fund’s NAV. The Fund could also be delayed or hindered in its enforcement of rights against an issuer, guarantor or counterparty. The degree of credit risk depends on the issuer’s or counterparty’s financial condition and on the terms of the securities.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Interest Rate Maturity Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | Interest Rate/Maturity Risk is the risk that the value of the Fund’s fixed-income assets will decline because of rising interest rates. In general, securities with longer maturities or durations are more sensitive to interest rate changes. Changing interest rates, including rates that fall below zero, may have unpredictable effects on the markets and the Fund’s investments, may result in heightened market volatility, may impact the liquidity of fixed-income securities and of the Fund, and may detract from Fund performance. A low or negative interest rate environment could cause the Fund’s earnings to fall below the Fund’s expense ratio, resulting in a negative yield and a decline in the Fund’s share price. 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.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Debt Extension Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | Debt Extension Risk is the risk that when interest rates rise an issuer will exercise its right to pay principal on certain debt securities held by the Fund later than expected. This will cause the value of the security, and the Fund’s NAV, to decrease, and the Fund may lose opportunities to invest in higher yielding securities.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Prepayment or Call Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | Prepayment (or Call) Risk is the risk that an issuer could exercise its right to pay principal on callable debt securities held by the Fund earlier than expected. Issuers may be more likely to prepay when interest rates fall, when credit spreads change, or when an issuer’s credit quality improves. 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 in lower yielding securities, which may reduce the Fund’s returns. The Fund may also lose any premium it paid to purchase the securities.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Income Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | 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.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Foreign Securities Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | Foreign Securities Risk is the risk that investing in foreign (non-U.S.) securities may result in the Fund experiencing more rapid and extreme changes in value than a fund that invests exclusively in securities of U.S. companies, due to less liquid markets and adverse economic, political, diplomatic, financial, and regulatory factors. Foreign governments may impose limitations on foreigners’ ownership of interests in local issuers, restrictions on the ability to repatriate assets, and may also impose taxes. Any of these events could cause the value of the Fund’s investments to decline. Foreign banks, agents and securities depositories that hold the Fund’s foreign assets may be subject to little or no regulatory oversight over, or independent evaluation, of their operations. Additional costs associated with investments in foreign securities may include higher custodial fees than those applicable to domestic custodial arrangements and transaction costs of foreign currency conversions. Unless the Fund has hedged its foreign currency exposure, foreign securities risk also involves the risk of negative foreign currency rate fluctuations, which may cause the value of securities denominated in such foreign currency (or other instruments through which the Fund has exposure to foreign currencies) to decline in value. Currency exchange rates may fluctuate significantly over short periods of time. Currency hedging strategies, if used, are not always successful. For instance, forward foreign currency exchange contracts, if used by the Fund, could reduce performance if there are unanticipated changes in currency exchange rates.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Market Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | 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, or volatility in the equity markets. Market disruptions caused by local or regional events such as financial institution failures, war, acts of terrorism, the spread of infectious illness (including epidemics and pandemics) or other public health issues, recessions or other events or adverse investor sentiment could have a significant impact on the Fund and its investments. Such events could result in the Fund’s shares trading at increased premiums or discounts to the Fund’s NAV. During periods of market disruption or other abnormal market conditions, the Fund’s exposure to the risks described elsewhere in this summary will likely increase.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Liquidity Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | 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 NAV. At times, such differences may be significant.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Rule 144A Securities Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | Rule 144A Securities Risk is the risk that limitations on the resale of Rule 144A securities may have an adverse effect on their marketability and may prevent the Fund from disposing of them promptly at reasonable prices. There can be no assurance that an active trading market will exist at any time for such securities. Transaction costs may be higher for Rule 144A securities, and such securities may be difficult to value and may have significant volatility.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Index Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | Index Risk is the risk that the Fund would not necessarily buy or sell a security unless that security is added to or removed from, respectively, the Underlying Index, even if that security generally is underperforming, because unlike many investment companies, the Fund does not utilize an investing strategy that seeks returns in excess of the Underlying Index. Additionally, the Fund rebalances and/or reconstitutes its portfolio in accordance with the Underlying Index, and, therefore, any changes to the Underlying Index’s rebalance and/or reconstitution schedule will result in corresponding changes to the Fund’s rebalance and/or reconstitution schedule.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Tracking Error Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | Tracking Error Risk is the risk that the Fund’s performance may vary from the performance of the Underlying Index as a result of creation and redemption activity, transaction costs, expenses and other factors. Market disruptions, regulatory restrictions or other abnormal market conditions could have an adverse effect on the Fund's ability to adjust its exposure to required levels in order to track its Index or cause delays in the Underlying Index's rebalancing schedule. During any such delay, it is possible that the Underlying Index, and, in turn, the Fund will deviate from the Underlying Index's stated methodology and therefore experience returns different than those that would have been achieved under a normal rebalancing or reconstitution schedule.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Sampling Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | Sampling Risk is the risk that the Fund’s use of a representative sampling approach may not work as intended and result in increased tracking error because the securities selected for the Fund in the aggregate may vary from the investment profile of the Underlying Index. Additionally, the use of a representative sampling approach may result in the Fund holding a smaller number of securities than the Underlying Index, and, as a result, an adverse development to an issuer of securities that the Fund holds could result in a greater decline in NAV than would be the case if the Fund held all of the securities in the Underlying Index.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Authorized Participant Concentration Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | 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 or unwilling to proceed with creation and/or redemption orders with respect to the Fund and no other Authorized Participant is able or willing 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.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Calculation Methodology Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | 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 Underlying Index guaranteed. A security included in the Underlying Index may not exhibit the characteristic or provide the specific exposure for which it was selected and consequently a Fund’s holdings may not exhibit returns consistent with that characteristic or exposure.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Market Trading Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | 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.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Concentration Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | Concentration Risk is the risk that, if the Fund is concentrated in a particular industry or group of industries, the Fund is likely to present more risks than a fund that is broadly diversified over several industries or groups of industries. Compared to the broad market, an individual industry may be more strongly affected by changes in the economic climate, broad market shifts, moves in a particular dominant stock or regulatory changes. •Financial Sector Risk is the risk that the financial sector can be significantly affected by changes in interest rates, government regulation, the rate of corporate and consumer debt defaulted, price competition, and the availability and cost of capital, among other factors.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Derivatives Risks [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | 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. The use of derivatives is a highly specialized activity that involves investment techniques and risks different from those associated with investments in more traditional securities and instruments. •Futures Contracts Risk is the risk that there will be imperfect correlation between the change in market value of the Fund’s securities and the price of futures contracts, which may result in the strategy not working as intended; the possible inability of the Fund to sell or close out a futures contract at the desired time or price; losses due to unanticipated market movements, which potentially are unlimited; and the possible inability of NTI to correctly predict the direction of securities’ prices, interest rates, currency exchange rates and other economic factors, which may make the Fund’s returns more volatile or increase the risk of loss.•Options Contracts Risk Options contracts give the holder of the option the right to buy (or to sell) a position in a security or in a contract to the writer of the option, at a certain price. They are subject to correlation risk because there may be an imperfect correlation between the options and the securities markets that cause a given transaction to fail to achieve its objectives. The successful use of options depends on the investment adviser’s ability to predict correctly future price fluctuations and the degree of correlation between the options and securities markets. Exchanges can limit the number of positions that can be held or controlled by the Fund or the investment adviser, thus limiting the ability to implement the Fund’s strategies.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | New Fund Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | New Fund Risk is the risk that the Fund will not grow to or maintain an economically viable size, in which case it may experience greater tracking error to its Underlying Index than it otherwise would at higher asset levels, or it could ultimately liquidate without shareholder approval. The timing of such liquidation may not be favorable and could have negative tax consequences for shareholders. From time to time, an Authorized Participant, a third-party investor, the Fund’s adviser or an affiliate of the Fund’s adviser, may invest in the Fund and hold its investment for a specific period of time in order to facilitate commencement of the Fund’s operations or for the Fund to achieve size or scale. There can be no assurance that any such entity would not redeem its investment or that the size of the Fund would be maintained at such levels, which could negatively impact the Fund. The Fund’s Distributor does not maintain a secondary market in the shares.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | TBA Transactions Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | TBA Transactions Risk is the risk of loss if the securities received are less favorable than what was anticipated by the Fund when entering into the TBA transaction. TBA transactions also involve the risk that the counterparty will fail to deliver the securities, exposing the Fund to further losses. Default or bankruptcy of a counterparty to a TBA transaction would expose the Fund to possible losses because of adverse market action, expenses or delays in connection with the purchase or sale of the pools of mortgage pass-through securities specified in the TBA transaction. Whether or not the Fund takes delivery of the securities at the termination date of a TBA transaction, the Fund will nonetheless be exposed to changes in the value of the underlying investments during the term of the agreement.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Securities Lending Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | 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.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Valuation Risk [Member] | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Risk [Text Block] | rr_RiskTextBlock | 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.
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| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| Management Fees | rr_ManagementFeesOverAssets | 0.12% | ||||||
| Distribution (12b-1) Fees | rr_DistributionAndService12b1FeesOverAssets | none | ||||||
| Other Expenses | rr_OtherExpensesOverAssets | 0.01% | ||||||
| Total Annual Fund Operating Expenses | rr_ExpensesOverAssets | 0.13% | ||||||
| Expense Reimbursement | rr_FeeWaiverOrReimbursementOverAssets | (0.01%) | [1] | |||||
| Total Annual Fund Operating Expenses After Expense Reimbursement | rr_NetExpensesOverAssets | 0.12% | ||||||
| 1 Year | rr_ExpenseExampleYear01 | $ 12 | ||||||
| 3 Years | rr_ExpenseExampleYear03 | 41 | ||||||
| 5 Years | rr_ExpenseExampleYear05 | 72 | ||||||
| 10 Years | rr_ExpenseExampleYear10 | $ 165 | ||||||
| 2022 | rr_AnnualReturn2022 | (16.32%) | ||||||
| 2023 | rr_AnnualReturn2023 | 8.59% | ||||||
| 2024 | rr_AnnualReturn2024 | 2.02% | ||||||
| Highest Quarterly Return, Label | rr_HighestQuarterlyReturnLabel | Best Quarter | ||||||
| Highest Quarterly Return, Date | rr_BarChartHighestQuarterlyReturnDate | Dec. 31, 2023 | ||||||
| Highest Quarterly Return | rr_BarChartHighestQuarterlyReturn | 8.32% | ||||||
| Lowest Quarterly Return, Label | rr_LowestQuarterlyReturnLabel | Worst Quarter | ||||||
| Lowest Quarterly Return, Date | rr_BarChartLowestQuarterlyReturnDate | Mar. 31, 2022 | ||||||
| Lowest Quarterly Return | rr_BarChartLowestQuarterlyReturn | (7.45%) | ||||||
| One Year | rr_AverageAnnualReturnYear01 | 2.02% | ||||||
| Since Inception of Fund | rr_AverageAnnualReturnSinceInception | (2.68%) | ||||||
| Inception Date of Fund | rr_AverageAnnualReturnInceptionDate | Sep. 20, 2021 | ||||||
| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | After Taxes on Distributions | FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| One Year | rr_AverageAnnualReturnYear01 | 0.13% | ||||||
| Since Inception of Fund | rr_AverageAnnualReturnSinceInception | (4.16%) | ||||||
| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | After Taxes on Distributions and Sale of Shares | FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| One Year | rr_AverageAnnualReturnYear01 | 1.18% | ||||||
| Since Inception of Fund | rr_AverageAnnualReturnSinceInception | (2.65%) | ||||||
| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Bloomberg U.S. Aggregate Bond Index | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| One Year | rr_AverageAnnualReturnYear01 | 1.25% | [2],[3] | |||||
| Since Inception of Fund | rr_AverageAnnualReturnSinceInception | (2.52%) | [2],[3] | |||||
| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Bloomberg US Corporate Total Return Value Unhedged Index | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| One Year | rr_AverageAnnualReturnYear01 | 2.13% | [3] | |||||
| Since Inception of Fund | rr_AverageAnnualReturnSinceInception | (2.45%) | [3] | |||||
| FlexShares ESG & Climate Investment Grade Corporate Core Index Fund | Northern Trust ESG & Climate Investment Grade US Corporate Core Index℠ | ||||||||
| Risk/Return: | rr_RiskReturnAbstract | |||||||
| One Year | rr_AverageAnnualReturnYear01 | 2.35% | [3] | |||||
| Since Inception of Fund | rr_AverageAnnualReturnSinceInception | (2.40%) | [3] | |||||
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