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Nuveen Credit Income Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Nuveen Credit Income Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The investment objective of the Fund is to provide total return, with an emphasis on a high level of current income.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The following tables describe the fees and expenses that you may pay if you buy, hold and sell shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Nuveen Mutual Funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial advisor and in “How You Can Buy and Sell Shares” on page 43 of the Fund’s prospectus and “Purchase and Redemption of Fund Shares” on page S-77 of the Fund’s statement of additional information. In addition, more information about sales charge discounts and waivers for purchases of shares through specific financial intermediaries is set forth in the appendix to the Fund’s prospectus entitled “Variations in Sales Charge Reductions and Waivers Available Through Certain Intermediaries.” 
The tables and examples below do not reflect any commissions that shareholders may be required to pay directly to their financial intermediaries when buying or selling Class I shares. 
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
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 July 31, 2024
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. During the fiscal year ended June 30, 2022, the Fund’s portfolio turnover rate was 120% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 120.00%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock The contingent deferred sales charge on Class C shares applies only to redemptions within 12 months of purchase.
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Nuveen Mutual Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
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 mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then either redeem or do not redeem your shares at the end of a period. The example also assumes that your investment has a 5% return each year, that the Fund’s operating expenses remain the same and that the fee waivers currently in place are not renewed beyond July 31, 2024. 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
Under normal circumstances, the Fund invests at least 80% of the sum of its net assets and the amount of any borrowings for investment purposes in credit and credit-related instruments. Credit and credit-related instruments include, but are not limited to:
· domestic and foreign corporate debt obligations, including bonds, notes, debentures, commercial paper and other obligations of corporations to pay interest and repay principal;
· fixed and floating rate loans, including senior loans and secured and unsecured junior loans, in an amount not to exceed 30% of the Fund’s net assets;
· residential and commercial mortgage-backed securities;
· asset-backed securities;
· preferred securities and contingent capital securities (sometimes referred to as “CoCos”) in an aggregate amount not to exceed 20% of the Fund’s net assets;
· interests in senior, mezzanine, and subordinated/equity classes or “tranches” of collateralized loan obligations (“CLOs”);
· U.S. government securities (securities issued or guaranteed by the U.S. government or its agencies or instrumentalities); and
· debt obligations of foreign governments.
The Fund will invest at least 65% of its assets in securities rated lower than investment grade at the time of purchase or in unrated bonds of comparable quality as determined by the Fund’s sub-adviser (securities commonly referred to as “high yield” securities or “junk” bonds). There is no minimum rating requirement and no limitation on the average maturity or average effective duration of securities held by the Fund.
The Fund may invest without limitation in debt obligations of foreign corporations and governments. However, no more than 30% of the Fund’s total assets may be invested in securities of governmental and corporate issuers that are located in emerging market countries.
The Fund may invest in securities that have not been registered under the Securities Act of 1933, but that may be resold to qualified institutional buyers in accordance with the provisions of Rule 144A under the Securities Act of 1933 (“Rule 144A securities”).
The Fund may invest in exchange-traded funds (“ETFs”), closed-end funds, and other investment companies (“investment companies”).
The Fund’s sub-adviser makes buy, sell, and hold decisions using a “top-down” approach, which begins with the formulation of the sub-adviser’s general economic outlook. Following this, various sectors and industries are analyzed and selected for investment. Finally, the sub-adviser selects individual securities within these sectors or industries. The sub-adviser also analyzes expected changes to the yield curve under multiple market conditions to help define maturity and duration selection.
The Fund may utilize the following derivatives: options; futures contracts; options on futures contracts; foreign currency contracts; options on foreign currencies; swap agreements, including interest rate swaps, currency swaps, total return swaps and credit default swaps; and options on swap agreements. The Fund may use these derivatives in an attempt to manage market risk, currency risk, credit risk and yield curve risk, to manage the effective maturity or duration of securities in the Fund’s portfolio or for speculative purposes in an effort to increase the Fund’s yield or to enhance returns. 
The use of a derivative is speculative if the Fund is primarily seeking to enhance returns, rather than offset the risk of other positions. 
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
The value of your investment in this Fund will change daily. You could lose money by investing in the Fund. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The principal risks of investing in the Fund listed below are presented alphabetically to facilitate your ability to find particular risks and compare them with the risks of other funds. Each risk summarized below is considered a "principal risk" of investing in the Fund, regardless of the order in which it appears.
Active Management Risk—The Fund’s sub-adviser actively manages the Fund’s investments. Consequently, the Fund is subject to the risk that the investment techniques and risk analyses employed by the Fund’s sub-adviser may not produce the desired results. This could cause the Fund to lose value or its investment results to lag relevant benchmarks or other funds with similar objectives.
Bond Market Liquidity Risk—Reductions in trading activity or dealer inventories of bonds, which provide an indication of the ability of financial intermediaries to “make markets” in those bonds, have the potential to decrease liquidity and increase price volatility in the fixed income markets in which the Fund invests, particularly during periods of economic or market stress. In addition, federal banking regulations may cause certain dealers to reduce their inventories of bonds, which may further decrease the Fund’s ability to buy or sell bonds. As a result of this decreased liquidity, the Fund may have to accept a lower price to sell a security, sell other securities to raise cash, or give up an investment opportunity, any of which could have a negative effect on performance. If the Fund needed to sell large blocks of bonds to meet shareholder redemption requests or to raise cash, those sales could further reduce the bonds’ prices and hurt performance. 
Call Risk—If, during periods of falling interest rates, an issuer exercises its right to prepay principal on its higher-yielding debt securities held by the Fund, the Fund may have to reinvest in securities with lower yields or higher risk of default, which may adversely impact the Fund’s performance. 
Collateralized Loan Obligations Risk—A CLO is an asset-backed security whose underlying collateral is a pool of loans, which may include, among others, domestic and foreign floating rate and fixed rate senior secured loans, senior unsecured loans, and subordinate corporate loans, including loans that may be rated below investment grade. In addition to the risks associated with loans and high yield securities, CLOs are subject to the risk that distributions from the collateral may not be adequate to make interest or other payments; the quality of the collateral may decline in value or default; the Fund may invest in tranches of CLOs that are subordinate to other tranches; and the CLO’s manager may perform poorly. CLOs may charge management and other administrative fees, which are in addition to those of the Fund. 
Contingent Capital Security Risk—CoCos have loss absorption mechanisms benefitting the issuer built into their terms. Upon the occurrence of a specified trigger or event, CoCos may be subject to automatic conversion into the issuer’s common stock, which likely will have declined in value and which will be subordinate to the issuer’s other classes of securities, or to an automatic write-down of the principal amount of the securities, potentially to zero, which could result in the Fund losing a portion or all of its investment in such securities. CoCos are often rated below investment grade and are subject to the risks of high yield securities. 
Credit Risk—Credit risk is the risk that an issuer or other obligated party of a security may be, or perceived (whether by market participants, rating agencies, pricing services or otherwise) to be, unable or unwilling to make dividend, interest and principal payments when due and the related risk that the value of a security may decline because of concerns about the issuer’s ability or willingness to make such payments. Because the Fund invests at least 65% of the value of its assets in high yield securities, the Fund's credit risks are greater than those of funds that buy only investment grade securities. 
Credit Spread Risk—Credit spread risk is the risk that credit spreads (i.e., the difference in yield between securities that is due to differences in their credit quality) may increase when the market believes that bonds generally have a greater risk of default. Increasing credit spreads may reduce the market values of the Fund’s debt securities. Credit spreads often increase more for lower rated and unrated securities than for investment grade securities. In addition, when credit spreads increase, reductions in market value will generally be greater for longer-maturity securities. 
Currency Risk—Changes in currency exchange rates will affect the value of non-U.S. securities, the value of dividends and interest earned from such securities, gains and losses realized on the sale of such securities, and derivative transactions tied to such securities. A strong U.S. dollar relative to these other currencies will adversely affect the value of the Fund’s portfolio. 
Cybersecurity Risk—Cybersecurity risk is the risk of an unauthorized breach and access to Fund assets, customer data (including private shareholder information), or proprietary information, or the risk of an incident occurring that causes the Fund, its investment adviser or sub-adviser, custodian, transfer agent, distributor or other service provider or a financial intermediary to suffer a data breach, data corruption or lose operational functionality. Successful cyber-attacks or other cyber-failures or events affecting the Fund or its service providers may adversely impact the Fund or its shareholders. Additionally, a cybersecurity breach could affect the issuers in which the Fund invests, which may cause the Fund’s investments to lose value. 
Derivatives Risk—The use of derivatives involves additional risks and transaction costs which could leave the Fund in a worse position than if it had not used these instruments. Derivative instruments can be used to acquire or to transfer the risk and returns of a security or other asset without buying or selling the security or asset. These instruments may entail investment exposures that are greater than their cost would suggest. As a result, a small investment in derivatives can result in losses that greatly exceed the original investment. Derivatives can be highly volatile, illiquid and difficult to value. An over-the-counter derivative transaction between the Fund and a counterparty that is not cleared through a central counterparty also involves the risk that a loss may be sustained as a result of the failure of the counterparty to the contract to make required payments. The payment obligation for a cleared derivative transaction is guaranteed by a central counterparty, which exposes the Fund to the creditworthiness of the central counterparty. 
Emerging Markets Risk—The risk of foreign investment often increases in countries with emerging markets or that are otherwise economically tied to emerging market countries. For example, these countries may have more unstable governments than developed countries and their economies may be based on only a few industries. Emerging market countries may also have less stringent regulation of accounting, auditing, financial reporting and recordkeeping requirements, which would affect the Fund’s ability to evaluate potential portfolio companies. As a result, there could be less information about issuers in emerging market countries, which could negatively affect the ability of the Fund’s sub-adviser to evaluate local companies or their potential impact on the Fund’s performance. Because their financial markets may be very small, prices of financial instruments in emerging market countries may be volatile and difficult to determine. Financial instruments of issuers in these countries may have lower overall liquidity than those of issuers in more developed countries. In addition, foreign investors such as the Fund are subject to a variety of special restrictions in many emerging market countries. Shareholder claims and regulatory actions that are available in the U.S. may be difficult or impossible to pursue in emerging market countries. 
ETF Risk—An ETF is subject to the risks of the underlying securities that it holds. In addition, for index-based ETFs, the performance of an ETF may diverge from the performance of such index (commonly known as tracking error). ETFs are subject to fees and expenses (like management fees and operating expenses) that do not apply to an index, and the Fund will indirectly bear its proportionate share of any such fees and expenses paid by the ETFs in which it invests. Moreover, ETF shares may trade at a premium or discount to their net asset value. As ETFs trade on an exchange, they are subject to the risks of any exchange-traded instrument, including: (i) an active trading market for its shares may not develop or be maintained, (ii) market makers or authorized participants may decide to reduce their role or step away from these activities in times of market stress, (iii) trading of its shares may be halted by the exchange, and (iv) its shares may be delisted from the exchange. 
Foreign Investment Risk—Non-U.S. issuers or U.S. issuers with significant non-U.S. operations may be subject to risks in addition to those of issuers located in or that principally operate in the United States as a result of, among other things, political, social and economic developments abroad and different legal, regulatory and tax environments. Foreign investments may also have lower liquidity and be more difficult to value than investments in U.S. issuers. To the extent the Fund invests a significant portion of its assets in the securities of companies in a single country or region, it may be more susceptible to adverse conditions affecting that country or region. Foreign investments may also be subject to risk of loss because of more or less foreign government regulation, less public information, less stringent investor protections and less stringent accounting, corporate governance, financial reporting and disclosure standards.  
Frequent Trading Risk—The Fund's portfolio turnover rate may exceed 100%. Frequent trading of portfolio securities may produce capital gains, which are taxable to shareholders when distributed. Frequent trading may also increase the amount of commissions or mark-ups to broker-dealers that the Fund pays when it buys and sells securities, which may detract from the Fund’s performance. 
High Yield Securities Risk—High yield securities, which are rated below investment grade and commonly referred to as “junk” bonds, and unrated securities of comparable quality are high risk investments that may cause income and principal losses for the Fund. They generally are considered to be speculative with respect to the ability to pay interest and repay  
principal, have greater credit risk, are less liquid, are more likely to experience a default and have more volatile prices than investment grade securities. 
Illiquid Investments Risk—Certain securities held by the Fund are illiquid investments, which may be difficult to sell for the value at which they are carried, if at all, or at any price within the desired time frame. 
Income Risk—The Fund's income could decline during periods of falling interest rates or when the Fund experiences defaults on debt securities or defaults or deferrals on preferred securities it holds.  
Interest Rate Risk—Interest rate risk is the risk that the value of the Fund’s fixed-rate securities will decline because of rising interest rates. Very low or negative interest rates may magnify interest rate risk. Changing interest rates, including rates that fall below zero, may have unpredictable effects on markets, result in heightened market volatility and detract from the Fund’s performance to the extent that it is exposed to such interest rates. Fixed-rate securities may be subject to a greater risk of rising interest rates than would normally be the case due to the effect of potential government fiscal policy initiatives and resulting market reaction to those initiatives. When interest rates change, the values of longer-duration fixed-rate securities usually change more than the values of shorter-duration fixed-rate securities. Conversely, fixed-rate securities with shorter durations or maturities will be less volatile but may provide lower returns than fixed-rate securities with longer durations or maturities. Rising interest rates also may lengthen the duration of securities with call features, since exercise of the call becomes less likely as interest rates rise, which in turn will make the securities more sensitive to changes in interest rates and result in even steeper price declines in the event of further interest rate increases. In especially low interest rate environments, the income generated by the Fund’s investments may be less than the expenses of the Fund or a particular share class of the Fund, especially for share classes with higher ongoing expenses, in which case the Fund or a particular share class of the Fund would not generate sufficient net income to pay a dividend. 
Loan Risk—The lack of an active trading market for certain loans may impair the ability of the Fund to realize full value in the event of the need to sell a loan and may make it difficult to value such loans. Portfolio transactions in loans may settle in as short as seven days but typically can take up to two or three weeks, and in some cases much longer. As a result of these extended settlement periods, the Fund may incur losses if it is required to sell other investments or temporarily borrow to meet its cash needs, including satisfying redemption requests. The risks associated with unsecured loans, which are not backed by a security interest in any specific collateral, are higher than those for comparable loans that are secured by specific collateral. For secured loans, there is a risk that the value of any collateral securing a loan in which the Fund has an interest may decline and that the collateral may not be sufficient to cover the amount owed on the loan. Interests in loans made to finance highly leveraged companies or transactions such as corporate acquisitions may be especially vulnerable to adverse changes in economic or market conditions. Loans may have restrictive covenants limiting the ability of a borrower to further encumber its assets. However, in periods of high demand by lenders like the Fund for loan investments, borrowers may limit these covenants and weaken a lender’s ability to access collateral securing the loan; reprice the credit risk associated with the borrower; and mitigate potential loss. The Fund may experience relatively greater realized or unrealized losses or delays and expenses in enforcing its rights with respect to loans with fewer restrictive covenants. Additionally, loans may not be considered “securities” and, as a result, the Fund may not be entitled to rely on the anti-fraud or other protections of the securities laws. Because junior loans have a lower place in an issuer’s capital structure and may be unsecured, junior loans involve a higher degree of overall risk than senior loans of the issuer. The Fund's investments in floating rate loans that pay interest based on the London Interbank Offered Rate (LIBOR) may experience increased volatility and/or illiquidity during the transition away from LIBOR, which is scheduled to be phased out. 
Market Risk—The market value of the Fund’s investments may go up or down, sometimes rapidly or unpredictably and for short or extended periods of time, due to the particular circumstances of individual issuers or due to general conditions impacting issuers more broadly. Global economies and financial markets have become highly interconnected, and thus economic, market or political conditions or events in one country or region might adversely impact the value of the Fund’s investments whether or not the Fund invests in such country or region. Events such as war, terrorism, natural and environmental disasters and the spread of infectious illnesses or other public health emergencies may have a severe negative impact on the global economy, could cause financial markets to experience extreme volatility and losses, and could result in the disruption of trading and the reduction of liquidity in many instruments. Additionally, as inflation increases, the value of the Fund’s assets can decline. 
Mortgage- and Asset-Backed Securities Risk—These securities generally can be prepaid at any time, and prepayments that occur either more quickly or more slowly than expected can adversely impact the value of such securities. They are also subject to extension risk, which is the risk that rising interest rates could cause mortgages or other obligations underlying the securities to be prepaid more slowly than expected, thereby lengthening the duration of  
such securities, increasing their sensitivity to interest rate changes and causing their prices to decline. Mortgage-backed securities are particularly sensitive to prepayment risk, given that the term to maturity for mortgage loans is generally substantially longer than the expected lives of those securities. A mortgage-backed security may be negatively affected by the quality of the mortgages underlying such security, the credit quality of its issuer or guarantor, and the nature and structure of its credit support. Mortgage- and asset-backed securities that are not backed by the full faith and credit of the U.S. government are subject to the risk of default on the underlying mortgage, loan or asset, particularly during periods of economic downturn. 
Other Investment Companies Risk—When the Fund invests in other investment companies, including ETFs, you bear both your proportionate share of Fund expenses and, indirectly, the expenses of the other investment companies. Furthermore, the Fund is exposed to the risks to which the other investment companies may be subject.  
Preferred Security Risk—Preferred securities generally are subordinated to bonds and other debt instruments in a company’s capital structure and therefore will be subject to greater credit risk than those debt instruments. In addition, preferred securities are subject to other risks, such as having no or limited voting rights, being subject to special redemption rights, having distributions deferred or skipped, having floating interest rates or dividends, which may result in a decline in value in a falling interest rate environment, having fixed interest rates or dividends, which may result in a decline in value in a rising interest rate environment, having limited liquidity, changing or unfavorable tax treatments and possibly being issued by companies in heavily regulated industries. 
Rule 144A Securities Risk—The market for Rule 144A securities typically is less active than the market for publicly-traded securities. Rule 144A securities carry the risk that their liquidity may become impaired and the Fund may be unable to dispose of the securities promptly or at current market value. 
Sovereign Debt Risk—Sovereign debt instruments are subject to the risk that a governmental entity may delay or refuse to pay interest or repay principal on its sovereign debt. This may be due to, for example, cash flow problems, insufficient foreign currency reserves, political considerations, the relative size of the governmental entity’s debt position in relation to the economy or the failure to put in place economic reforms required by the International Monetary Fund or other multilateral agencies. 
Unrated Security Risk—Unrated securities determined by the Fund’s sub-adviser to be of comparable quality to rated securities which the Fund may purchase may pay a higher interest rate than such rated securities and be subject to a greater risk of illiquidity or price changes. Less public information is typically available about unrated securities or issuers than rated securities or issuers. 
U.S. Government Securities Risk—U.S. government securities are guaranteed only as to the timely payment of interest and the payment of principal when held to maturity. Accordingly, the current market values for these securities will fluctuate with changes in interest rates. Securities issued or guaranteed by U.S. government agencies and instrumentalities are supported by varying degrees of credit but generally are not backed by the full faith and credit of the U.S. government. No assurance can be given that the U.S. government will provide financial support to its agencies and instrumentalities if it is not obligated by law to do so. 
Valuation Risk—The debt securities in which the Fund invests typically are valued by a pricing service utilizing a range of market-based inputs and assumptions, including price quotations obtained from broker-dealers making markets in such instruments, cash flows and transactions for comparable instruments. There is no assurance that the Fund will be able to buy or sell a portfolio security at the price established by the pricing service, which could result in a gain or loss to the Fund. Pricing services generally price debt securities assuming orderly transactions of an institutional “round lot” size, but some trades may occur in smaller, “odd lot” sizes, often at lower prices than institutional round lot trades. Over certain time periods, such differences could materially impact the performance of the Fund, which may not be sustainable. Alternative pricing services may incorporate different assumptions and inputs into their valuation methodologies, potentially resulting in different values for the same securities. As a result, if the Fund were to change pricing services, or if the Fund’s pricing service were to change its valuation methodology, there could be a material impact, either positive or negative, on the Fund’s net asset value. 
Risk Lose Money [Text] rr_RiskLoseMoney The value of your investment in this Fund will change daily. You could lose money by investing in the Fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Fund Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The following bar chart and table provide some indication of the potential risks of investing in the Fund. The Fund’s performance information prior to July 7, 2020 reflects the Fund’s performance using an investment objective and investment strategies that differed from those currently in place. In view of these changes, the Fund’s performance record prior to this date might be less pertinent for investors considering whether to purchase shares of the Fund. The  
Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. Updated performance information is available at www.nuveen.com/performance or by calling (800) 257-8787. 
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart below shows the variability of the Fund’s performance from year to year for Class A shares.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone (800) 257-8787
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.nuveen.com/performance
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading   Class A Annual Total Return*
Bar Chart Narrative [Text Block] rr_BarChartNarrativeTextBlock
The bar chart below shows the variability of the Fund’s performance from year to year for Class A shares. The bar chart and highest/lowest quarterly returns that follow do not reflect sales charges, and if these charges were reflected, the returns would be less than those shown. 
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The bar chart and highest/lowest quarterly returns that follow do not reflect sales charges, and if these charges were reflected, the returns would be less than those shown.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
During the ten-year period ended December 31, 2021, the Fund’s highest and lowest quarterly returns were 10.49%
and -18.29%, respectively, for the quarters ended June 30, 2020 and March 31, 2020. 
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns for the Periods Ended December 31, 2021
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate All 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 are not relevant to investors who hold Fund shares in tax-deferred accounts such as IRAs or employer-sponsored retirement plans.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns are shown for Class A shares only; after-tax returns for other share classes will vary.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock
The table below shows the variability of the Fund’s average annual returns and how they compare over the time periods indicated with those of a broad measure of market performance and an index of funds with similar investment objectives. All 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. After-tax returns are shown for Class A shares only; after-tax returns for other share classes will vary. Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as IRAs or employer-sponsored retirement plans. 
Both the bar chart and the table assume that all distributions have been reinvested. Performance reflects fee waivers, if any, in effect during the periods presented. If any such waivers had not been in place, returns would have been reduced. 
Nuveen Credit Income Fund | Class A  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.75%
Maximum Deferred Sales Charge (Load) (as a percentage of the lesser of purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none [1]
Maximum Sales Charge (Load) Imposed on Reinvested Dividends rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Exchange Fee rr_ExchangeFeeOverRedemption none
Annual Low Balance Account Fee (for accounts under $1,000) rr_MaximumAccountFee $ 15 [2]
Management Fees rr_ManagementFeesOverAssets 0.60%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.30%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.15%
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.15%) [3]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 1.00%
1 Year rr_ExpenseExampleYear01 $ 572
3 Years rr_ExpenseExampleYear03 798
5 Years rr_ExpenseExampleYear05 1,053
10 Years rr_ExpenseExampleYear10 1,783
1 Year rr_ExpenseExampleNoRedemptionYear01 572
3 Years rr_ExpenseExampleNoRedemptionYear03 798
5 Years rr_ExpenseExampleNoRedemptionYear05 1,053
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,783
2012 rr_AnnualReturn2012 17.89% [4]
2013 rr_AnnualReturn2013 8.52% [4]
2014 rr_AnnualReturn2014 (0.28%) [4]
2015 rr_AnnualReturn2015 (11.95%) [4]
2016 rr_AnnualReturn2016 21.46% [4]
2017 rr_AnnualReturn2017 7.30% [4]
2018 rr_AnnualReturn2018 (4.61%) [4]
2019 rr_AnnualReturn2019 16.53% [4]
2020 rr_AnnualReturn2020 0.94% [4]
2021 rr_AnnualReturn2021 4.64% [4]
Year to Date Return, Label rr_YearToDateReturnLabel year-to-date total return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Sep. 30, 2022
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (14.04%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 10.49%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (18.29%)
1 Year rr_AverageAnnualReturnYear01 (0.27%)
5 Years rr_AverageAnnualReturnYear05 3.71%
10 Years rr_AverageAnnualReturnYear10 5.05%
Nuveen Credit Income Fund | Class C  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of the lesser of purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther 1.00% [1]
Maximum Sales Charge (Load) Imposed on Reinvested Dividends rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Exchange Fee rr_ExchangeFeeOverRedemption none
Annual Low Balance Account Fee (for accounts under $1,000) rr_MaximumAccountFee $ 15 [2]
Management Fees rr_ManagementFeesOverAssets 0.60%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.30%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.90%
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.15%) [3]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 1.75%
1 Year rr_ExpenseExampleYear01 $ 178
3 Years rr_ExpenseExampleYear03 571
5 Years rr_ExpenseExampleYear05 1,002
10 Years rr_ExpenseExampleYear10 2,200
1 Year rr_ExpenseExampleNoRedemptionYear01 178
3 Years rr_ExpenseExampleNoRedemptionYear03 571
5 Years rr_ExpenseExampleNoRedemptionYear05 1,002
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,200
1 Year rr_AverageAnnualReturnYear01 3.88%
5 Years rr_AverageAnnualReturnYear05 3.94%
10 Years rr_AverageAnnualReturnYear10 4.95%
Nuveen Credit Income Fund | Class I  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of the lesser of purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none [1]
Maximum Sales Charge (Load) Imposed on Reinvested Dividends rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Exchange Fee rr_ExchangeFeeOverRedemption none
Annual Low Balance Account Fee (for accounts under $1,000) rr_MaximumAccountFee $ 15 [2]
Management Fees rr_ManagementFeesOverAssets 0.60%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.30%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.90%
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.15%) [3]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 0.75%
1 Year rr_ExpenseExampleYear01 $ 77
3 Years rr_ExpenseExampleYear03 260
5 Years rr_ExpenseExampleYear05 472
10 Years rr_ExpenseExampleYear10 1,083
1 Year rr_ExpenseExampleNoRedemptionYear01 77
3 Years rr_ExpenseExampleNoRedemptionYear03 260
5 Years rr_ExpenseExampleNoRedemptionYear05 472
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,083
1 Year rr_AverageAnnualReturnYear01 4.74%
5 Years rr_AverageAnnualReturnYear05 4.94%
10 Years rr_AverageAnnualReturnYear10 5.83%
Nuveen Credit Income Fund | (return after taxes on distributions) | Class A  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (2.04%)
5 Years rr_AverageAnnualReturnYear05 1.33%
10 Years rr_AverageAnnualReturnYear10 2.24%
Nuveen Credit Income Fund | (return after taxes on distributions and sale of Fund shares) | Class A  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (0.18%)
5 Years rr_AverageAnnualReturnYear05 1.77%
10 Years rr_AverageAnnualReturnYear10 2.61%
Nuveen Credit Income Fund | Bloomberg High Yield 2% Issuers Capped Index (reflects no deduction for fees, expenses or taxes)  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 5.26% [5]
5 Years rr_AverageAnnualReturnYear05 6.28% [5]
10 Years rr_AverageAnnualReturnYear10 6.82% [5]
Nuveen Credit Income Fund | Lipper Global High Yield Funds Category Average (reflects no deduction for taxes or sales loads)  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 3.84% [6]
5 Years rr_AverageAnnualReturnYear05 4.93% [6]
10 Years rr_AverageAnnualReturnYear10 5.62% [6]
[1] The contingent deferred sales charge on Class C shares applies only to redemptions within 12 months of purchase.
[2] Fee applies to the following types of accounts under $1,000 held directly with the Fund: individual retirement accounts (IRAs), Coverdell Education Savings Accounts and accounts established pursuant to the Uniform Transfers to Minors Act (UTMA) or Uniform Gifts to Minors Act (UGMA).
[3] The Fund’s investment adviser has agreed to waive fees and/or reimburse expenses through July 31, 2024 so that the total annual operating expenses of the Fund (excluding 12b-1 distribution and/or service fees, interest expenses, taxes, acquired fund fees and expenses, fees incurred in acquiring and disposing of portfolio securities and extraordinary expenses) do not exceed 0.75% of the average daily net assets of any class of Fund shares. This expense limitation may be terminated or modified prior to July 31, 2024 only with the approval of the Board of Directors of the Fund.
[4] Class A year-to-date total return as of September 30, 2022 was -14.04%. The performance of the other share classes will differ due to their different expense structures.
[5]
An issuer-constrained version of the U.S. Corporate High-Yield Index that covers the U.S. dollar denominated, non-investment grade, fixed-rate, taxable corporate bond market.
[6]
Represents the average annualized total return for all reporting funds in the Lipper Global High Yield Funds Category.