497

SIDLEY AUSTIN LLP 787 SEVENTH AVENUE NEW YORK, NY 10019 +1 212 839 5300 +1 212 839 5599 FAX   AMERICA • ASIA PACIFIC • EUROPE

August 31, 2018

VIA EDGAR

U.S. Securities and Exchange Commission

100 F Street, N.E.

Washington, D.C. 20549

Re: BlackRock Global Long/Short Credit Fund, a series of BlackRock Funds IV

Securities Act File No. 333-224373

Investment Company Act File No. 811-23341                                                         

Ladies and Gentlemen:

On behalf of BlackRock Funds IV, attached for filing are exhibits containing interactive data format risk/return summary information that mirrors the risk/return summary information in the Prospectus of BlackRock Global Long/Short Credit Fund (the “Fund”), dated August 10, 2018, as filed pursuant to Rule 497(c) under the Securities Act of 1933 on August 10, 2018 (the “497 Filing”). The purpose of this filing is to submit the 497 Filing in XBRL for the Fund.

Any questions or comments on the 497 Filing should be directed to the undersigned at (212) 839-8615.

Very truly yours,

/s/ Jesse C. Kean

Jesse C. Kean

Enclosures

cc: Benjamin Archibald, Esq.

BlackRock Advisors, LLC

Sidley Austin (NY) LLP is a Delaware limited liability partnership doing business as Sidley Austin LLP and practicing in affiliation with other Sidley Austin partnerships.

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Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	497
Document Period End Date	dei_DocumentPeriodEndDate	Jan. 31, 2018
Registrant Name	dei_EntityRegistrantName	BlackRock Funds IV
Central Index Key	dei_EntityCentralIndexKey	0001738074
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Aug. 10, 2018
Document Effective Date	dei_DocumentEffectiveDate	Aug. 10, 2018
Prospectus Date	rr_ProspectusDate	Aug. 10, 2018

XML

Class K | BlackRock Global Long/Short Credit Fund

Fund Overview

Investment Objective

The investment objective of BlackRock Global Long/Short Credit Fund (the “Fund”), a series of BlackRock Funds IV (the “Trust”), is to seek absolute total returns over a complete market cycle.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold Class K Shares of the Fund.

Annual Fund Operating Expenses
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses	Class K BlackRock Global Long/Short Credit Fund Class K Shares
Management Fee	0.90%	[1],[2]
Distribution and/or Service (12b-1) Fees	none
Other Expenses	0.89%	[3]
Interest Expense	0.73%
Dividend Expense	0.04%
Miscellaneous Other Expenses	0.12%
Acquired Fund Fees and Expenses	0.01%	[3]
Total Annual Fund Operating Expenses	1.80%
Fee Waivers and/or Expense Reimbursements		[1],[4]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	1.80%	[1],[4]

Example:

This 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 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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example	1 Year	3 Years	5 Years	10 Years
Class K | BlackRock Global Long/Short Credit Fund | Class K Shares | USD ($)	183	566	975	2,116

Portfolio Turnover:

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 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.

The Fund has not commenced operations as of the date of this prospectus, but it is expected that BlackRock Global Long/Short Credit Fund, a series of BlackRock Funds^SM (the “Predecessor Fund”), will be reorganized into the Fund.

During the most recent fiscal year, the Predecessor Fund’s portfolio turnover rate was 229% of the average value of its portfolio.

Principal Investment Strategies of the Fund

The Fund seeks to provide absolute total returns over a complete market cycle through diversified long and short exposure to the global fixed-income markets. A complete market cycle for fixed income funds such as the Fund is typically three to five years.

Under normal circumstances, the Fund invests at least 80% of its total assets in credit-related instruments. Credit-related instruments include, but are not limited to, U.S. Government and agency securities, foreign government and supranational debt securities, corporate bonds, including bonds of companies principally engaged in the aircraft or air transportation industries, mortgage-related securities and asset-backed securities, collateralized debt and loan obligations, including bonds collateralized by aircraft and/or aircraft equipment, emerging market debt securities, preferred securities, structured products, mezzanine securities, senior secured floating rate and fixed rate loans or debt, second lien or other subordinated or unsecured floating rate and fixed rate loans or debt, convertible debt securities, and derivatives with similar economic characteristics. The Fund may invest in fixed, variable and floating rate instruments, including participations and assignments, of any duration or maturity.

Under normal circumstances, the Fund anticipates it will allocate a substantial amount (approximately 40% or more, unless market conditions are not deemed favorable by BlackRock, in which case the Fund would invest at least 30%) of its total assets in securities (or derivatives with similar economic characteristics) of (i) foreign government issuers, (ii) issuers organized or located outside the United States, (iii) issuers whose securities primarily trade in a market located outside the United States, or (iv) issuers doing a substantial amount of business outside the United States, which the Fund considers to be companies that derive at least 50% of their revenue or profits from business outside the United States or have at least 50% of their sales or assets outside the United States. The Fund will allocate its assets among various regions and countries, including the United States (but in no less than three different countries).

The Fund may invest in credit-related instruments rated below investment grade or deemed equivalent by Fund management, which are commonly referred to as “junk bonds.”

The Fund may invest in non-U.S. dollar denominated investments, including investments denominated in European and Asian currencies and in other non-U.S. and emerging market currencies. The Fund’s investments in non-U.S. dollar based assets may be made on a currency hedged or unhedged basis.

The Fund may invest up to 20% of its total assets in equity instruments, including common stock, depositary receipts, rights, warrants and other instruments whose price is linked to the value of common stock. The Fund may hold long or short positions in equity instruments, and may invest in equity instruments of issuers of any market capitalization.

The Fund may also gain both long and short exposure to credit-related instruments by entering into a series of purchase and sale contracts or by investing in, among other instruments, swaps, including total return, credit default, index and interest rate swaps; options; forward contracts; futures contracts and options on futures contracts that provide long or short exposure to other credit obligations; credit-linked notes that provide long or short exposure to other credit obligations; repurchase agreements; reverse repurchase agreements; dollar rolls; exchange-traded funds and closed-end registered investment companies, which may be managed by BlackRock or one of its affiliates; and other similar transactions.

The Fund may engage in short sales for hedging purposes or to enhance total return. The Fund also may make short sales “against the box” without limitation. In this type of short sale, at the time of the sale, the Fund owns or has the immediate and unconditional right to acquire the identical security at no additional cost.

As part of its normal operations, the Fund may hold high quality money market securities and invest in money market funds, including affiliated money market funds, pending investments or when it expects to need cash to pay redeeming shareholders. The Fund also may invest in these securities in order to achieve its investment goal. Money market securities are short term securities consisting primarily of short term U.S. Government securities, U.S. Government agency securities, securities issued by U.S. Government sponsored enterprises and U.S. Government instrumentalities, bank obligations, commercial paper, including asset backed commercial paper, corporate notes and repurchase agreements.

The Fund may engage in active and frequent trading of portfolio securities to achieve its primary investment strategies.

The Fund may borrow from banks for investment purposes.

Principal Risks of Investing in the Fund

Risk is inherent in all investing. The value of your investment in the Fund, as well as the amount of return you receive on your investment, may fluctuate significantly from day to day and over time. You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments. The following is a summary description of the principal risks of investing in the Fund.

• Air Transportation Industry Risk — The air transportation industry can be significantly affected by competition within the industry, domestic and foreign economies, government regulation, labor relations, and the price of fuel. Airline deregulation has substantially diminished the government’s role in the air transport industry while promoting an increased level of competition. However, regulations and policies of various domestic and foreign governments can still affect the profitability of individual carriers as well as the entire industry.

• Borrowing Risk — Borrowing may exaggerate changes in the net asset value of Fund shares and in the return on the Fund’s portfolio. Borrowing will cost the Fund interest expense and other fees. The costs of borrowing may reduce the Fund’s return. Borrowing may cause the Fund to liquidate positions when it may not be advantageous to do so to satisfy its obligations.

• Collateralized Debt Obligations Risk — In addition to the typical risks associated with fixed-income securities and asset-backed securities, collateralized debt obligations (“CDOs”) carry additional risks including, but not limited to: (i) the possibility that distributions from collateral securities will not be adequate to make interest or other payments; (ii) the risk that the collateral may default or decline in value or be downgraded, if rated by a nationally recognized statistical rating organization; (iii) the Fund may invest in tranches of CDOs that are subordinate to other tranches; (iv) the structure and complexity of the transaction and the legal documents could lead to disputes among investors regarding the characterization of proceeds; (v) the investment return achieved by the Fund could be significantly different than those predicted by financial models; (vi) the lack of a readily available secondary market for CDOs; (vii) the risk of forced “fire sale” liquidation due to technical defaults such as coverage test failures; and (viii) the CDO’s manager may perform poorly. In addition, investments in CDOs may be characterized by the Fund as illiquid securities.

• Convertible Securities Risk — The market value of a convertible security performs like that of a regular debt security; that is, if market interest rates rise, the value of a convertible security usually falls. In addition, convertible securities are subject to the risk that the issuer will not be able to pay interest or dividends when due, and their market value may change based on changes in the issuer’s credit rating or the market’s perception of the issuer’s creditworthiness. Since it derives a portion of its value from the common stock into which it may be converted, a convertible security is also subject to the same types of market and issuer risks that apply to the underlying common stock.

• Corporate Loans Risk — Commercial banks and other financial institutions or institutional investors make corporate loans to companies that need capital to grow or restructure. Borrowers generally pay interest on corporate loans at rates that change in response to changes in market interest rates such as the London Interbank Offered Rate (“LIBOR”) or the prime rates of U.S. banks. As a result, the value of corporate loan investments is generally less exposed to the adverse effects of shifts in market interest rates than investments that pay a fixed rate of interest. The market for corporate loans may be subject to irregular trading activity and wide bid/ask spreads. In addition, transactions in corporate loans may settle on a delayed basis. As a result, the proceeds from the sale of corporate loans may not be readily available to make additional investments or to meet the Fund’s redemption obligations. To the extent the extended settlement process gives rise to short-term liquidity needs, the Fund may hold additional cash, sell investments or temporarily borrow from banks and other lenders. The corporate loans in which the Fund invests are usually rated below investment grade.

• Debt Securities Risk — Debt securities, such as bonds, involve interest rate risk, credit risk, extension risk, and prepayment risk, among other things.
  
  Interest Rate Risk — The market value of bonds and other fixed-income securities changes in response to interest rate changes and other factors. Interest rate risk is the risk that prices of bonds and other fixed-income securities will increase as interest rates fall and decrease as interest rates rise.
  
  The Fund may be subject to a greater risk of rising interest rates due to the current period of historically low rates. For example, if interest rates increase by 1%, assuming a current portfolio duration of ten years, and all other factors being equal, the value of the Fund’s investments would be expected to decrease by 10%. The magnitude of these fluctuations in the market price of bonds and other fixed-income securities is generally greater for those securities with longer maturities. Fluctuations in the market price of the Fund’s investments will not affect interest income derived from instruments already owned by the Fund, but will be reflected in the Fund’s net asset value. The Fund may lose money if short-term or long-term interest rates rise sharply in a manner not anticipated by Fund management.
  
  To the extent the Fund invests in debt securities that may be prepaid at the option of the obligor (such as mortgage-backed securities), the sensitivity of such securities to changes in interest rates may increase (to the detriment of the Fund) when interest rates rise. Moreover, because rates on certain floating rate debt securities typically reset only periodically, changes in prevailing interest rates (and particularly sudden and significant changes) can be expected to cause some fluctuations in the net asset value of the Fund to the extent that it invests in floating rate debt securities.
  
  These basic principles of bond prices also apply to U.S. Government securities. A security backed by the “full faith and credit” of the U.S. Government is guaranteed only as to its stated interest rate and face value at maturity, not its current market price. Just like other fixed-income securities, government-guaranteed securities will fluctuate in value when interest rates change.
  
  A general rise in interest rates has the potential to cause investors to move out of fixed-income securities on a large scale, which may increase redemptions from funds that hold large amounts of fixed-income securities. Heavy redemptions could cause the Fund to sell assets at inopportune times or at a loss or depressed value and could hurt the Fund’s performance.
  
  Credit Risk — Credit risk refers to the possibility that the issuer of a debt security (i.e., the borrower) will not be able to make payments of interest and principal when due. Changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Fund’s investment in that issuer. The degree of credit risk depends on both the financial condition of the issuer and the terms of the obligation.
  
  Extension Risk — When interest rates rise, certain obligations will be paid off by the obligor more slowly than anticipated, causing the value of these obligations to fall.
  
  Prepayment Risk — When interest rates fall, certain obligations will be paid off by the obligor more quickly than originally anticipated, and the Fund may have to invest the proceeds in securities with lower yields.

• Derivatives Risk — The Fund’s use of derivatives may increase its costs, reduce the Fund’s returns and/or increase volatility. Derivatives involve significant risks, including:
  
  Volatility Risk — Volatility is defined as the characteristic of a security, an index or a market to fluctuate significantly in price within a short time period. A risk of the Fund’s use of derivatives is that the fluctuations in their values may not correlate with the overall securities markets.
  
  Counterparty Risk — Derivatives are also subject to counterparty risk, which is the risk that the other party in the transaction will not fulfill its contractual obligation.
  
  Market and Liquidity Risk — The possible lack of a liquid secondary market for derivatives and the resulting inability of the Fund to sell or otherwise close a derivatives position could expose the Fund to losses and could make derivatives more difficult for the Fund to value accurately.
  
  Valuation Risk — Valuation may be more difficult in times of market turmoil since many investors and market makers may be reluctant to purchase complex instruments or quote prices for them.
  
  Hedging Risk — Hedges are sometimes subject to imperfect matching between the derivative and the underlying security, and there can be no assurance that the Fund’s hedging transactions will be effective. The use of hedging may result in certain adverse tax consequences.
  
  Tax Risk — Certain aspects of the tax treatment of derivative instruments, including swap agreements and commodity-linked derivative instruments, are currently unclear and may be affected by changes in legislation, regulations or other legally binding authority. Such treatment may be less favorable than that given to a direct investment in an underlying asset and may adversely affect the timing, character and amount of income the Fund realizes from its investments.
  
  Regulatory Risk — Derivative contracts, including, without limitation, swaps, currency forwards and non-deliverable forwards, are subject to regulation under the Dodd-Frank Wall Street Reform and Consumer Protection Act (“Dodd-Frank Act”) in the United States and under comparable regimes in Europe, Asia and other non-U.S. jurisdictions. Under the Dodd-Frank Act, certain derivatives are subject to margin requirements and swap dealers are required to collect margin from the Fund with respect to such derivatives. Specifically, regulations are now in effect that require swap dealers to post and collect variation margin (comprised of specified liquid instruments and subject to a required haircut) in connection with trading of over-the-counter (“OTC”) swaps with the Fund. Shares of investment companies (other than certain money market funds) may not be posted as collateral under these regulations. Requirements for posting of initial margin in connection with OTC swaps will be phased-in through 2020. In addition, regulations adopted by prudential regulators that will begin to take effect in 2019 will require certain bank-regulated counterparties and certain of their affiliates to include in certain financial contracts, including many derivatives contracts, terms that delay or restrict the rights of counterparties, such as the Fund, to terminate such contracts, foreclose upon collateral, exercise other default rights or restrict transfers of credit support in the event that the counterparty and/or its affiliates are subject to certain types of resolution or insolvency proceedings. The implementation of these requirements with respect to derivatives, as well as regulations under the Dodd-Frank Act regarding clearing, mandatory trading and margining of other derivatives may increase the costs and risks to the Fund of trading in these instruments and, as a result, may affect returns to investors in the Fund.
  
  Risks Specific to Certain Derivatives Used by the Fund

  Swaps – Swap agreements are two-party contracts entered into for periods ranging from a few weeks to more than one year. In a standard “swap” transaction, two parties agree to exchange the returns (or differentials in rates of return) earned or realized on particular predetermined investments or instruments, which can be adjusted for an interest factor. Swap agreements involve the risk that the party with whom the Fund has entered into the swap will default on its obligation to pay the Fund and the risk that the Fund will not be able to meet its obligations to pay the other party to the agreement.
  
  Credit Default Swaps – Credit default swaps involve special risks in addition to those mentioned above because they are difficult to value, are highly susceptible to liquidity and credit risk, and generally pay a return to the party that has paid the premium only in the event of an actual default by the issuer of the underlying obligation (as opposed to a credit downgrade or other indication of financial difficulty). The protection “buyer” in a credit default contract may be obligated to pay the protection “seller” an up front payment or a periodic stream of payments over the term of the contract provided generally that no credit event on a reference obligation has occurred. If a credit event occurs, the seller generally must pay the buyer the “par value” (full notional value) of the swap in exchange for an equal face amount of deliverable obligations of the reference entity described in the swap, or the seller may be required to deliver the related net cash amount, if the swap is cash settled. The Fund may be either the buyer or seller in the transaction.
  
  Forward Foreign Currency Exchange Contracts – Forward foreign currency exchange transactions are over-the counter contracts to purchase or sell a specified amount of a specified currency or multinational currency unit at a price and future date set at the time of the contract. Forward foreign currency exchange contracts do not eliminate fluctuations in the value of non-U.S. securities but rather allow the Fund to establish a fixed rate of exchange for a future point in time. This strategy can have the effect of reducing returns and minimizing opportunities for gain.

  To the extent derivatives are utilized to implement the Fund’s investment strategies, the transactions may involve the risks described herein. For example, to the extent the Fund gains short exposure to a security through a derivative instrument, the Fund will be subject to risks associated with short sales that are described below.

• Dividend Risk — Because certain of the corporate loans held by the Fund will have floating or variable interest rates, the amounts of the Fund’s distributions to its stockholders are expected to vary with fluctuations in market interest rates. Generally, when market interest rates fall, the amount of the distributions to stockholders will likewise decrease.

• Emerging Markets Risk — Emerging markets are riskier than more developed markets because they tend to develop unevenly and may never fully develop. Investments in emerging markets may be considered speculative. Emerging markets are more likely to experience hyperinflation and currency devaluations, which adversely affect returns to U.S. investors. In addition, many emerging securities markets have far lower trading volumes and less liquidity than developed markets.

• Event Risk — Event risk is the risk that corporate issuers may undergo restructurings, such as mergers, leveraged buyouts, takeovers, or similar events financed by increased debt. As a result of the added debt, the credit quality and market value of a company’s bonds and/or other debt securities may decline significantly.

• Foreign Securities Risk — Foreign investments often involve special risks not present in U.S. investments that can increase the chances that the Fund will lose money. These risks include:

• The Fund generally holds its foreign securities and cash in foreign banks and securities depositories, which may be recently organized or new to the foreign custody business and may be subject to only limited or no regulatory oversight.

• Changes in foreign currency exchange rates can affect the value of the Fund’s portfolio.

• The economies of certain foreign markets may not compare favorably with the economy of the United States with respect to such issues as growth of gross national product, reinvestment of capital, resources and balance of payments position.

• The governments of certain countries may prohibit or impose substantial restrictions on foreign investments in their capital markets or in certain industries.

• Many foreign governments do not supervise and regulate stock exchanges, brokers and the sale of securities to the same extent as does the United States and may not have laws to protect investors that are comparable to U.S. securities laws.

• Settlement and clearance procedures in certain foreign markets may result in delays in payment for or delivery of securities not typically associated with settlement and clearance of U.S. investments.

• The European financial markets have recently experienced volatility and adverse trends due to concerns about economic downturns in, or rising government debt levels of, several European countries. These events may spread to other countries in Europe. These events may affect the value and liquidity of certain of the Fund’s investments.

• High Portfolio Turnover Risk — The Fund may engage in active and frequent trading of its portfolio securities. High portfolio turnover (more than 100%) may result in increased transaction costs to the Fund, including brokerage commissions, dealer mark-ups and other transaction costs on the sale of the securities and on reinvestment in other securities. The sale of Fund portfolio securities may result in the realization and/or distribution to shareholders of higher capital gains or losses as compared to a fund with less active trading policies. These effects of higher than normal portfolio turnover may adversely affect Fund performance.

• Junk Bonds Risk — Although junk bonds generally pay higher rates of interest than investment grade bonds, junk bonds are high risk investments that are considered speculative and may cause income and principal losses for the Fund.

• Leverage Risk — Some transactions may give rise to a form of economic leverage. These transactions may include, among others, derivatives, and may expose the Fund to greater risk and increase its costs. The use of leverage may cause the Fund to liquidate portfolio positions when it may not be advantageous to do so to satisfy its obligations or to meet any required asset segregation requirements. Increases and decreases in the value of the Fund’s portfolio will be magnified when the Fund uses leverage.

• Liquidity Risk — Liquidity risk exists when particular investments are difficult to purchase or sell. The Fund’s investments in illiquid securities may reduce the returns of the Fund because it may be difficult to sell the illiquid securities at an advantageous time or price. To the extent that the Fund’s principal investment strategies involve derivatives or securities with substantial market and/or credit risk, the Fund will tend to have the greatest exposure to liquidity risk. Liquidity risk may be the result of, among other things, the reduced number and capacity of traditional market participants to make a market in fixed-income securities or the lack of an active market. Liquid investments may become illiquid or less liquid after purchase by the Fund, particularly during periods of market turmoil. Illiquid and relatively less liquid 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. This may be magnified in a rising interest rate environment or other circumstances where investor redemptions from fixed-income mutual funds may be higher than normal. In addition, when there is illiquidity in the market for certain securities, the Fund, due to limitations on illiquid investments, may be subject to purchase and sale restrictions.

• Market Risk and Selection Risk — Market risk is the risk that one or more markets in which the Fund invests will go down in value, including the possibility that the markets will go down sharply and unpredictably. Selection risk is the risk that the securities selected by Fund management will underperform the markets, the relevant indices or the securities selected by other funds with similar investment objectives and investment strategies. This means you may lose money.

• Mezzanine Securities Risk — Mezzanine securities carry the risk that the issuer will not be able to meet its obligations and that the equity securities purchased with the mezzanine investments may lose value.

• Mortgage- and Asset-Backed Securities Risks — Mortgage- and asset-backed securities represent interests in “pools” of mortgages or other assets, including consumer loans or receivables held in trust. Mortgage- and asset-backed securities are subject to credit, interest rate, prepayment and extension risks. These securities also are subject to risk of default on the underlying mortgage or asset, particularly during periods of economic downturn. Small movements in interest rates (both increases and decreases) may quickly and significantly reduce the value of certain mortgage-backed securities.

• Preferred Securities Risk — Preferred securities may pay fixed or adjustable rates of return. Preferred securities are subject to issuer-specific and market risks applicable generally to equity securities. In addition, a company’s preferred securities generally pay dividends only after the company makes required payments to holders of its bonds and other debt. For this reason, the value of preferred securities will usually react more strongly than bonds and other debt to actual or perceived changes in the company’s financial condition or prospects. Preferred securities of smaller companies may be more vulnerable to adverse developments than preferred stock of larger companies.

• Repurchase Agreements and Purchase and Sale Contracts Risk — If the other party to a repurchase agreement or purchase and sale contract defaults on its obligation under the agreement, the Fund may suffer delays and incur costs or lose money in exercising its rights under the agreement. If the seller fails to repurchase the security in either situation and the market value of the security declines, the Fund may lose money.

• Reverse Repurchase Agreements Risk — Reverse repurchase agreements involve the sale of securities held by the Fund with an agreement to repurchase the securities at an agreed-upon price, date and interest payment. Reverse repurchase agreements involve the risk that the other party may fail to return the securities in a timely manner or at all. The Fund could lose money if it is unable to recover the securities and the value of the collateral held by the Fund, including the value of the investments made with cash collateral, is less than the value of the securities. These events could also trigger adverse tax consequences to the Fund.

• Second Lien Loans Risk — Second lien loans generally are subject to similar risks as those associated with investments in senior loans. Because second lien loans are subordinated or unsecured and thus lower in priority of payment to senior loans, they are subject to the additional risk that the cash flow of the borrower and property securing the loan or debt, if any, may be insufficient to meet scheduled payments after giving effect to the senior secured obligations of the borrower.

• Senior Loans Risk — There is less readily available, reliable information about most senior loans than is the case for many other types of securities. An economic downturn generally leads to a higher non-payment rate, and a senior loan may lose significant value before a default occurs. Moreover, any specific collateral used to secure a senior loan may decline in value or become illiquid, which would adversely affect the senior loan’s value. No active trading market may exist for certain senior loans, which may impair the ability of the Fund to realize full value in the event of the need to sell a senior loan and which may make it difficult to value senior loans. Although senior loans in which the Fund will invest generally will be secured by specific collateral, there can be no assurance that liquidation of such collateral would satisfy the borrower’s obligation in the event of non-payment of scheduled interest or principal or that such collateral could be readily liquidated. To the extent that a senior loan is collateralized by stock in the borrower or its subsidiaries, such stock may lose all of its value in the event of the bankruptcy of the borrower. Uncollateralized senior loans involve a greater risk of loss. The senior loans in which the Fund invests are usually rated below investment grade.

• Short Sales Risk — Because making short sales in securities that it does not own exposes the Fund to the risks associated with those securities, such short sales involve speculative exposure risk. The Fund will incur a loss as a result of a short sale if the price of the security increases between the date of the short sale and the date on which the Fund replaces the security sold short. Short sale transactions involve leverage because they can provide investment exposure in an amount exceeding the initial investment.

• Small and Mid-Capitalization Company Risk — Companies with small or mid-size market capitalizations will normally have more limited product lines, markets and financial resources and will be dependent upon a more limited management group than larger capitalized companies. In addition, it is more difficult to get information on smaller companies, which tend to be less well known, have shorter operating histories, do not have significant ownership by large investors and are followed by relatively few securities analysts.

• 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, due, for example, to 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.

• Structured Products Risk — Holders of structured products bear risks of the underlying investments, index or reference obligation and are subject to counterparty risk. The Fund may have the right to receive payments only from the structured product, and generally does not have direct rights against the issuer or the entity that sold the assets to be securitized. Certain structured products may be thinly traded or have a limited trading market. In addition to the general risks associated with debt securities discussed herein, structured products carry additional risks, including, but not limited to: the possibility that distributions from collateral securities will not be adequate to make interest or other payments; the quality of the collateral may decline in value or default; and the possibility that the structured products are subordinate to other classes. Structured notes are based upon the movement of one or more factors, including currency exchange rates, interest rates, reference bonds and stock indices, and changes in interest rates and impact of these factors may cause significant price fluctuations. Additionally, changes in the reference instrument or security may cause the interest rate on the structured note to be reduced to zero.

Performance Information

The Fund has not commenced operations as of the date of this prospectus. The returns presented for the Fund reflect the performance of the Predecessor Fund. It is anticipated that on or about September 17, 2018, the Fund will acquire all of the assets, subject to the liabilities, of the Predecessor Fund through a tax-free reorganization (the “Reorganization”). As a result of the Reorganization, the Fund will adopt the performance and financial history of the Predecessor Fund. The Reorganization is being consummated in connection with a potential reconfiguration of the existing fund complexes overseen by the boards of directors/trustees of the BlackRock-advised funds. The Fund has the same investment objectives, strategies and policies, portfolio management team and contractual arrangements, including the same contractual fees and expenses, as the Predecessor Fund. As a result, the performance of the Fund would have been substantially similar to that of the Predecessor Fund.

The information shows you how the Predecessor Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. Class K Shares commenced operations on March 28, 2016, therefore the returns shown in the chart and table prior to the commencement date are those of Institutional Shares, which are not offered in this prospectus. The performance of Class K Shares would be substantially similar to Institutional Shares because Class K Shares and Institutional Shares are invested in the same portfolio of securities and performance would differ only to the extent that Institutional Shares and Class K Shares have different expenses. The actual returns of Class K Shares would have been higher than those of the Institutional Shares because Class K Shares have lower expenses than the Institutional Shares. The table compares the Predecessor Fund’s performance to that of the ICE BofAML 3-Month U.S. Treasury Bill Index. To the extent that dividends and distributions have been paid by the Predecessor Fund, the performance information of the Predecessor Fund in the chart and table assumes reinvestment of the dividends and distributions. As with all such investments, past performance (before and after taxes) is not an indication of future results. The table includes all applicable fees. If BlackRock and its affiliates had not waived or reimbursed certain Predecessor Fund expenses during these periods, the Predecessor Fund’s returns would have been lower. Updated information on the Fund’s performance, including its current net asset value, can be obtained by visiting http://www.blackrock.com or can be obtained by phone at (800) 882-0052.

Class K Shares
ANNUAL TOTAL RETURNS
BlackRock Global Long/Short Credit Fund
As of 12/31

During the periods shown in the bar chart, the highest return for a quarter was 2.48% (quarter ended December 31, 2012) and the lowest return for a quarter was –1.62% (quarter ended September 30, 2015). The year-to-date return as of June 30, 2018 was –0.29%.

As of 12/31/17
Average Annual Total Returns

Average Annual Total Returns - Class K - BlackRock Global Long/Short Credit Fund	1 Year	5 Years	Since Inception	Inception Date
Class K Shares	3.64%	2.18%	2.94%	Sep. 30, 2011
Class K Shares | Return After Taxes on Distributions	3.10%	1.10%	1.96%	Sep. 30, 2011
Class K Shares | Return After Taxes on Distributions and Sale of Fund Shares	2.11%	1.18%	1.83%	Sep. 30, 2011
ICE BofAML 3-Month U.S. Treasury Bill Index (Reflects no deduction for fees, expenses or taxes)	0.86%	0.27%	0.23%

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 the investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

[1] As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 34, BlackRock Advisors, LLC (“BlackRock”) has contractually agreed to waive the management fee with respect to any portion of the Fund’s assets estimated to be attributable to investments in other equity and fixed-income mutual funds and exchange-traded funds managed by BlackRock or its affiliates that have a contractual management fee, through November 30, 2019. The contractual agreement may be terminated upon 90 days’ notice by a majority of the non-interested trustees of the Trust or by a vote of a majority of the outstanding voting securities of the Fund.

[2] Management Fee is based on the management fee rate of the Predecessor Fund (as defined below).

[3] Other Expenses and Acquired Fund Fees and Expenses are based on estimated amounts for the current fiscal year, which are based on the expenses of the Predecessor Fund for its most recent fiscal year.

[4] As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 34, BlackRock has contractually agreed to waive and/or reimburse fees or expenses in order to limit Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements (excluding Dividend Expense, Interest Expense, Acquired Fund Fees and Expenses and certain other Fund expenses) to 1.15% of average daily net assets through November 30, 2019. The Fund may have to repay some of these waivers and/or reimbursements to BlackRock in the following two years. The contractual agreement may be terminated upon 90 days’ notice by a majority of the non-interested trustees of the Trust or by a vote of a majority of the outstanding voting securities of the Fund.

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Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	BlackRock Funds IV
Prospectus Date	rr_ProspectusDate	Aug. 10, 2018
Class K | BlackRock Global Long/Short Credit Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Overview
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The investment objective of BlackRock Global Long/Short Credit Fund (the “Fund”), a series of BlackRock Funds IV (the “Trust”), is to seek absolute total returns over a complete market cycle.
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 Class K Shares of the Fund.
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	November 30, 2019
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 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. The Fund has not commenced operations as of the date of this prospectus, but it is expected that BlackRock Global Long/Short Credit Fund, a series of BlackRock FundsSM (the “Predecessor Fund”), will be reorganized into the Fund. During the most recent fiscal year, the Predecessor Fund’s portfolio turnover rate was 229% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	229.00%
Other Expenses, New Fund, Based on Estimates [Text]	rr_OtherExpensesNewFundBasedOnEstimates	Other Expenses and Acquired Fund Fees and Expenses are based on estimated amounts for the current fiscal year, which are based on the expenses of the Predecessor Fund for its most recent fiscal year.
Acquired Fund Fees and Expenses, Based on Estimates [Text]	rr_AcquiredFundFeesAndExpensesBasedOnEstimates	Acquired Fund Fees and Expenses are based on estimated amounts for the current fiscal year, which are based on the expenses of the Predecessor Fund for its most recent fiscal year.
Expense Example [Heading]	rr_ExpenseExampleHeading	Example:
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This 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 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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies of the Fund
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund seeks to provide absolute total returns over a complete market cycle through diversified long and short exposure to the global fixed-income markets. A complete market cycle for fixed income funds such as the Fund is typically three to five years. Under normal circumstances, the Fund invests at least 80% of its total assets in credit-related instruments. Credit-related instruments include, but are not limited to, U.S. Government and agency securities, foreign government and supranational debt securities, corporate bonds, including bonds of companies principally engaged in the aircraft or air transportation industries, mortgage-related securities and asset-backed securities, collateralized debt and loan obligations, including bonds collateralized by aircraft and/or aircraft equipment, emerging market debt securities, preferred securities, structured products, mezzanine securities, senior secured floating rate and fixed rate loans or debt, second lien or other subordinated or unsecured floating rate and fixed rate loans or debt, convertible debt securities, and derivatives with similar economic characteristics. The Fund may invest in fixed, variable and floating rate instruments, including participations and assignments, of any duration or maturity. Under normal circumstances, the Fund anticipates it will allocate a substantial amount (approximately 40% or more, unless market conditions are not deemed favorable by BlackRock, in which case the Fund would invest at least 30%) of its total assets in securities (or derivatives with similar economic characteristics) of (i) foreign government issuers, (ii) issuers organized or located outside the United States, (iii) issuers whose securities primarily trade in a market located outside the United States, or (iv) issuers doing a substantial amount of business outside the United States, which the Fund considers to be companies that derive at least 50% of their revenue or profits from business outside the United States or have at least 50% of their sales or assets outside the United States. The Fund will allocate its assets among various regions and countries, including the United States (but in no less than three different countries). The Fund may invest in credit-related instruments rated below investment grade or deemed equivalent by Fund management, which are commonly referred to as “junk bonds.” The Fund may invest in non-U.S. dollar denominated investments, including investments denominated in European and Asian currencies and in other non-U.S. and emerging market currencies. The Fund’s investments in non-U.S. dollar based assets may be made on a currency hedged or unhedged basis. The Fund may invest up to 20% of its total assets in equity instruments, including common stock, depositary receipts, rights, warrants and other instruments whose price is linked to the value of common stock. The Fund may hold long or short positions in equity instruments, and may invest in equity instruments of issuers of any market capitalization. The Fund may also gain both long and short exposure to credit-related instruments by entering into a series of purchase and sale contracts or by investing in, among other instruments, swaps, including total return, credit default, index and interest rate swaps; options; forward contracts; futures contracts and options on futures contracts that provide long or short exposure to other credit obligations; credit-linked notes that provide long or short exposure to other credit obligations; repurchase agreements; reverse repurchase agreements; dollar rolls; exchange-traded funds and closed-end registered investment companies, which may be managed by BlackRock or one of its affiliates; and other similar transactions. The Fund may engage in short sales for hedging purposes or to enhance total return. The Fund also may make short sales “against the box” without limitation. In this type of short sale, at the time of the sale, the Fund owns or has the immediate and unconditional right to acquire the identical security at no additional cost. As part of its normal operations, the Fund may hold high quality money market securities and invest in money market funds, including affiliated money market funds, pending investments or when it expects to need cash to pay redeeming shareholders. The Fund also may invest in these securities in order to achieve its investment goal. Money market securities are short term securities consisting primarily of short term U.S. Government securities, U.S. Government agency securities, securities issued by U.S. Government sponsored enterprises and U.S. Government instrumentalities, bank obligations, commercial paper, including asset backed commercial paper, corporate notes and repurchase agreements. The Fund may engage in active and frequent trading of portfolio securities to achieve its primary investment strategies. The Fund may borrow from banks for investment purposes.
Risk [Heading]	rr_RiskHeading	Principal Risks of Investing in the Fund
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	Risk is inherent in all investing. The value of your investment in the Fund, as well as the amount of return you receive on your investment, may fluctuate significantly from day to day and over time. You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments. The following is a summary description of the principal risks of investing in the Fund. Air Transportation Industry Risk — The air transportation industry can be significantly affected by competition within the industry, domestic and foreign economies, government regulation, labor relations, and the price of fuel. Airline deregulation has substantially diminished the government’s role in the air transport industry while promoting an increased level of competition. However, regulations and policies of various domestic and foreign governments can still affect the profitability of individual carriers as well as the entire industry. Borrowing Risk — Borrowing may exaggerate changes in the net asset value of Fund shares and in the return on the Fund’s portfolio. Borrowing will cost the Fund interest expense and other fees. The costs of borrowing may reduce the Fund’s return. Borrowing may cause the Fund to liquidate positions when it may not be advantageous to do so to satisfy its obligations. Collateralized Debt Obligations Risk — In addition to the typical risks associated with fixed-income securities and asset-backed securities, collateralized debt obligations (“CDOs”) carry additional risks including, but not limited to: (i) the possibility that distributions from collateral securities will not be adequate to make interest or other payments; (ii) the risk that the collateral may default or decline in value or be downgraded, if rated by a nationally recognized statistical rating organization; (iii) the Fund may invest in tranches of CDOs that are subordinate to other tranches; (iv) the structure and complexity of the transaction and the legal documents could lead to disputes among investors regarding the characterization of proceeds; (v) the investment return achieved by the Fund could be significantly different than those predicted by financial models; (vi) the lack of a readily available secondary market for CDOs; (vii) the risk of forced “fire sale” liquidation due to technical defaults such as coverage test failures; and (viii) the CDO’s manager may perform poorly. In addition, investments in CDOs may be characterized by the Fund as illiquid securities. Convertible Securities Risk — The market value of a convertible security performs like that of a regular debt security; that is, if market interest rates rise, the value of a convertible security usually falls. In addition, convertible securities are subject to the risk that the issuer will not be able to pay interest or dividends when due, and their market value may change based on changes in the issuer’s credit rating or the market’s perception of the issuer’s creditworthiness. Since it derives a portion of its value from the common stock into which it may be converted, a convertible security is also subject to the same types of market and issuer risks that apply to the underlying common stock. Corporate Loans Risk — Commercial banks and other financial institutions or institutional investors make corporate loans to companies that need capital to grow or restructure. Borrowers generally pay interest on corporate loans at rates that change in response to changes in market interest rates such as the London Interbank Offered Rate (“LIBOR”) or the prime rates of U.S. banks. As a result, the value of corporate loan investments is generally less exposed to the adverse effects of shifts in market interest rates than investments that pay a fixed rate of interest. The market for corporate loans may be subject to irregular trading activity and wide bid/ask spreads. In addition, transactions in corporate loans may settle on a delayed basis. As a result, the proceeds from the sale of corporate loans may not be readily available to make additional investments or to meet the Fund’s redemption obligations. To the extent the extended settlement process gives rise to short-term liquidity needs, the Fund may hold additional cash, sell investments or temporarily borrow from banks and other lenders. The corporate loans in which the Fund invests are usually rated below investment grade. Debt Securities Risk — Debt securities, such as bonds, involve interest rate risk, credit risk, extension risk, and prepayment risk, among other things. Interest Rate Risk — The market value of bonds and other fixed-income securities changes in response to interest rate changes and other factors. Interest rate risk is the risk that prices of bonds and other fixed-income securities will increase as interest rates fall and decrease as interest rates rise. The Fund may be subject to a greater risk of rising interest rates due to the current period of historically low rates. For example, if interest rates increase by 1%, assuming a current portfolio duration of ten years, and all other factors being equal, the value of the Fund’s investments would be expected to decrease by 10%. The magnitude of these fluctuations in the market price of bonds and other fixed-income securities is generally greater for those securities with longer maturities. Fluctuations in the market price of the Fund’s investments will not affect interest income derived from instruments already owned by the Fund, but will be reflected in the Fund’s net asset value. The Fund may lose money if short-term or long-term interest rates rise sharply in a manner not anticipated by Fund management. To the extent the Fund invests in debt securities that may be prepaid at the option of the obligor (such as mortgage-backed securities), the sensitivity of such securities to changes in interest rates may increase (to the detriment of the Fund) when interest rates rise. Moreover, because rates on certain floating rate debt securities typically reset only periodically, changes in prevailing interest rates (and particularly sudden and significant changes) can be expected to cause some fluctuations in the net asset value of the Fund to the extent that it invests in floating rate debt securities. These basic principles of bond prices also apply to U.S. Government securities. A security backed by the “full faith and credit” of the U.S. Government is guaranteed only as to its stated interest rate and face value at maturity, not its current market price. Just like other fixed-income securities, government-guaranteed securities will fluctuate in value when interest rates change. A general rise in interest rates has the potential to cause investors to move out of fixed-income securities on a large scale, which may increase redemptions from funds that hold large amounts of fixed-income securities. Heavy redemptions could cause the Fund to sell assets at inopportune times or at a loss or depressed value and could hurt the Fund’s performance. Credit Risk — Credit risk refers to the possibility that the issuer of a debt security (i.e., the borrower) will not be able to make payments of interest and principal when due. Changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Fund’s investment in that issuer. The degree of credit risk depends on both the financial condition of the issuer and the terms of the obligation. Extension Risk — When interest rates rise, certain obligations will be paid off by the obligor more slowly than anticipated, causing the value of these obligations to fall. Prepayment Risk — When interest rates fall, certain obligations will be paid off by the obligor more quickly than originally anticipated, and the Fund may have to invest the proceeds in securities with lower yields. Derivatives Risk — The Fund’s use of derivatives may increase its costs, reduce the Fund’s returns and/or increase volatility. Derivatives involve significant risks, including: Volatility Risk — Volatility is defined as the characteristic of a security, an index or a market to fluctuate significantly in price within a short time period. A risk of the Fund’s use of derivatives is that the fluctuations in their values may not correlate with the overall securities markets. Counterparty Risk — Derivatives are also subject to counterparty risk, which is the risk that the other party in the transaction will not fulfill its contractual obligation. Market and Liquidity Risk — The possible lack of a liquid secondary market for derivatives and the resulting inability of the Fund to sell or otherwise close a derivatives position could expose the Fund to losses and could make derivatives more difficult for the Fund to value accurately. Valuation Risk — Valuation may be more difficult in times of market turmoil since many investors and market makers may be reluctant to purchase complex instruments or quote prices for them. Hedging Risk — Hedges are sometimes subject to imperfect matching between the derivative and the underlying security, and there can be no assurance that the Fund’s hedging transactions will be effective. The use of hedging may result in certain adverse tax consequences. Tax Risk — Certain aspects of the tax treatment of derivative instruments, including swap agreements and commodity-linked derivative instruments, are currently unclear and may be affected by changes in legislation, regulations or other legally binding authority. Such treatment may be less favorable than that given to a direct investment in an underlying asset and may adversely affect the timing, character and amount of income the Fund realizes from its investments. Regulatory Risk — Derivative contracts, including, without limitation, swaps, currency forwards and non-deliverable forwards, are subject to regulation under the Dodd-Frank Wall Street Reform and Consumer Protection Act (“Dodd-Frank Act”) in the United States and under comparable regimes in Europe, Asia and other non-U.S. jurisdictions. Under the Dodd-Frank Act, certain derivatives are subject to margin requirements and swap dealers are required to collect margin from the Fund with respect to such derivatives. Specifically, regulations are now in effect that require swap dealers to post and collect variation margin (comprised of specified liquid instruments and subject to a required haircut) in connection with trading of over-the-counter (“OTC”) swaps with the Fund. Shares of investment companies (other than certain money market funds) may not be posted as collateral under these regulations. Requirements for posting of initial margin in connection with OTC swaps will be phased-in through 2020. In addition, regulations adopted by prudential regulators that will begin to take effect in 2019 will require certain bank-regulated counterparties and certain of their affiliates to include in certain financial contracts, including many derivatives contracts, terms that delay or restrict the rights of counterparties, such as the Fund, to terminate such contracts, foreclose upon collateral, exercise other default rights or restrict transfers of credit support in the event that the counterparty and/or its affiliates are subject to certain types of resolution or insolvency proceedings. The implementation of these requirements with respect to derivatives, as well as regulations under the Dodd-Frank Act regarding clearing, mandatory trading and margining of other derivatives may increase the costs and risks to the Fund of trading in these instruments and, as a result, may affect returns to investors in the Fund. Risks Specific to Certain Derivatives Used by the Fund Swaps – Swap agreements are two-party contracts entered into for periods ranging from a few weeks to more than one year. In a standard “swap” transaction, two parties agree to exchange the returns (or differentials in rates of return) earned or realized on particular predetermined investments or instruments, which can be adjusted for an interest factor. Swap agreements involve the risk that the party with whom the Fund has entered into the swap will default on its obligation to pay the Fund and the risk that the Fund will not be able to meet its obligations to pay the other party to the agreement. Credit Default Swaps – Credit default swaps involve special risks in addition to those mentioned above because they are difficult to value, are highly susceptible to liquidity and credit risk, and generally pay a return to the party that has paid the premium only in the event of an actual default by the issuer of the underlying obligation (as opposed to a credit downgrade or other indication of financial difficulty). The protection “buyer” in a credit default contract may be obligated to pay the protection “seller” an up front payment or a periodic stream of payments over the term of the contract provided generally that no credit event on a reference obligation has occurred. If a credit event occurs, the seller generally must pay the buyer the “par value” (full notional value) of the swap in exchange for an equal face amount of deliverable obligations of the reference entity described in the swap, or the seller may be required to deliver the related net cash amount, if the swap is cash settled. The Fund may be either the buyer or seller in the transaction. Forward Foreign Currency Exchange Contracts – Forward foreign currency exchange transactions are over-the counter contracts to purchase or sell a specified amount of a specified currency or multinational currency unit at a price and future date set at the time of the contract. Forward foreign currency exchange contracts do not eliminate fluctuations in the value of non-U.S. securities but rather allow the Fund to establish a fixed rate of exchange for a future point in time. This strategy can have the effect of reducing returns and minimizing opportunities for gain. To the extent derivatives are utilized to implement the Fund’s investment strategies, the transactions may involve the risks described herein. For example, to the extent the Fund gains short exposure to a security through a derivative instrument, the Fund will be subject to risks associated with short sales that are described below. Dividend Risk — Because certain of the corporate loans held by the Fund will have floating or variable interest rates, the amounts of the Fund’s distributions to its stockholders are expected to vary with fluctuations in market interest rates. Generally, when market interest rates fall, the amount of the distributions to stockholders will likewise decrease. Emerging Markets Risk — Emerging markets are riskier than more developed markets because they tend to develop unevenly and may never fully develop. Investments in emerging markets may be considered speculative. Emerging markets are more likely to experience hyperinflation and currency devaluations, which adversely affect returns to U.S. investors. In addition, many emerging securities markets have far lower trading volumes and less liquidity than developed markets. Event Risk — Event risk is the risk that corporate issuers may undergo restructurings, such as mergers, leveraged buyouts, takeovers, or similar events financed by increased debt. As a result of the added debt, the credit quality and market value of a company’s bonds and/or other debt securities may decline significantly. Foreign Securities Risk — Foreign investments often involve special risks not present in U.S. investments that can increase the chances that the Fund will lose money. These risks include: The Fund generally holds its foreign securities and cash in foreign banks and securities depositories, which may be recently organized or new to the foreign custody business and may be subject to only limited or no regulatory oversight. Changes in foreign currency exchange rates can affect the value of the Fund’s portfolio. The economies of certain foreign markets may not compare favorably with the economy of the United States with respect to such issues as growth of gross national product, reinvestment of capital, resources and balance of payments position. The governments of certain countries may prohibit or impose substantial restrictions on foreign investments in their capital markets or in certain industries. Many foreign governments do not supervise and regulate stock exchanges, brokers and the sale of securities to the same extent as does the United States and may not have laws to protect investors that are comparable to U.S. securities laws. Settlement and clearance procedures in certain foreign markets may result in delays in payment for or delivery of securities not typically associated with settlement and clearance of U.S. investments. The European financial markets have recently experienced volatility and adverse trends due to concerns about economic downturns in, or rising government debt levels of, several European countries. These events may spread to other countries in Europe. These events may affect the value and liquidity of certain of the Fund’s investments. High Portfolio Turnover Risk — The Fund may engage in active and frequent trading of its portfolio securities. High portfolio turnover (more than 100%) may result in increased transaction costs to the Fund, including brokerage commissions, dealer mark-ups and other transaction costs on the sale of the securities and on reinvestment in other securities. The sale of Fund portfolio securities may result in the realization and/or distribution to shareholders of higher capital gains or losses as compared to a fund with less active trading policies. These effects of higher than normal portfolio turnover may adversely affect Fund performance. Junk Bonds Risk — Although junk bonds generally pay higher rates of interest than investment grade bonds, junk bonds are high risk investments that are considered speculative and may cause income and principal losses for the Fund. Leverage Risk — Some transactions may give rise to a form of economic leverage. These transactions may include, among others, derivatives, and may expose the Fund to greater risk and increase its costs. The use of leverage may cause the Fund to liquidate portfolio positions when it may not be advantageous to do so to satisfy its obligations or to meet any required asset segregation requirements. Increases and decreases in the value of the Fund’s portfolio will be magnified when the Fund uses leverage. Liquidity Risk — Liquidity risk exists when particular investments are difficult to purchase or sell. The Fund’s investments in illiquid securities may reduce the returns of the Fund because it may be difficult to sell the illiquid securities at an advantageous time or price. To the extent that the Fund’s principal investment strategies involve derivatives or securities with substantial market and/or credit risk, the Fund will tend to have the greatest exposure to liquidity risk. Liquidity risk may be the result of, among other things, the reduced number and capacity of traditional market participants to make a market in fixed-income securities or the lack of an active market. Liquid investments may become illiquid or less liquid after purchase by the Fund, particularly during periods of market turmoil. Illiquid and relatively less liquid 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. This may be magnified in a rising interest rate environment or other circumstances where investor redemptions from fixed-income mutual funds may be higher than normal. In addition, when there is illiquidity in the market for certain securities, the Fund, due to limitations on illiquid investments, may be subject to purchase and sale restrictions. Market Risk and Selection Risk — Market risk is the risk that one or more markets in which the Fund invests will go down in value, including the possibility that the markets will go down sharply and unpredictably. Selection risk is the risk that the securities selected by Fund management will underperform the markets, the relevant indices or the securities selected by other funds with similar investment objectives and investment strategies. This means you may lose money. Mezzanine Securities Risk — Mezzanine securities carry the risk that the issuer will not be able to meet its obligations and that the equity securities purchased with the mezzanine investments may lose value. Mortgage- and Asset-Backed Securities Risks — Mortgage- and asset-backed securities represent interests in “pools” of mortgages or other assets, including consumer loans or receivables held in trust. Mortgage- and asset-backed securities are subject to credit, interest rate, prepayment and extension risks. These securities also are subject to risk of default on the underlying mortgage or asset, particularly during periods of economic downturn. Small movements in interest rates (both increases and decreases) may quickly and significantly reduce the value of certain mortgage-backed securities. Preferred Securities Risk — Preferred securities may pay fixed or adjustable rates of return. Preferred securities are subject to issuer-specific and market risks applicable generally to equity securities. In addition, a company’s preferred securities generally pay dividends only after the company makes required payments to holders of its bonds and other debt. For this reason, the value of preferred securities will usually react more strongly than bonds and other debt to actual or perceived changes in the company’s financial condition or prospects. Preferred securities of smaller companies may be more vulnerable to adverse developments than preferred stock of larger companies. Repurchase Agreements and Purchase and Sale Contracts Risk — If the other party to a repurchase agreement or purchase and sale contract defaults on its obligation under the agreement, the Fund may suffer delays and incur costs or lose money in exercising its rights under the agreement. If the seller fails to repurchase the security in either situation and the market value of the security declines, the Fund may lose money. Reverse Repurchase Agreements Risk — Reverse repurchase agreements involve the sale of securities held by the Fund with an agreement to repurchase the securities at an agreed-upon price, date and interest payment. Reverse repurchase agreements involve the risk that the other party may fail to return the securities in a timely manner or at all. The Fund could lose money if it is unable to recover the securities and the value of the collateral held by the Fund, including the value of the investments made with cash collateral, is less than the value of the securities. These events could also trigger adverse tax consequences to the Fund. Second Lien Loans Risk — Second lien loans generally are subject to similar risks as those associated with investments in senior loans. Because second lien loans are subordinated or unsecured and thus lower in priority of payment to senior loans, they are subject to the additional risk that the cash flow of the borrower and property securing the loan or debt, if any, may be insufficient to meet scheduled payments after giving effect to the senior secured obligations of the borrower. Senior Loans Risk — There is less readily available, reliable information about most senior loans than is the case for many other types of securities. An economic downturn generally leads to a higher non-payment rate, and a senior loan may lose significant value before a default occurs. Moreover, any specific collateral used to secure a senior loan may decline in value or become illiquid, which would adversely affect the senior loan’s value. No active trading market may exist for certain senior loans, which may impair the ability of the Fund to realize full value in the event of the need to sell a senior loan and which may make it difficult to value senior loans. Although senior loans in which the Fund will invest generally will be secured by specific collateral, there can be no assurance that liquidation of such collateral would satisfy the borrower’s obligation in the event of non-payment of scheduled interest or principal or that such collateral could be readily liquidated. To the extent that a senior loan is collateralized by stock in the borrower or its subsidiaries, such stock may lose all of its value in the event of the bankruptcy of the borrower. Uncollateralized senior loans involve a greater risk of loss. The senior loans in which the Fund invests are usually rated below investment grade. Short Sales Risk — Because making short sales in securities that it does not own exposes the Fund to the risks associated with those securities, such short sales involve speculative exposure risk. The Fund will incur a loss as a result of a short sale if the price of the security increases between the date of the short sale and the date on which the Fund replaces the security sold short. Short sale transactions involve leverage because they can provide investment exposure in an amount exceeding the initial investment. Small and Mid-Capitalization Company Risk — Companies with small or mid-size market capitalizations will normally have more limited product lines, markets and financial resources and will be dependent upon a more limited management group than larger capitalized companies. In addition, it is more difficult to get information on smaller companies, which tend to be less well known, have shorter operating histories, do not have significant ownership by large investors and are followed by relatively few securities analysts. 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, due, for example, to 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. Structured Products Risk — Holders of structured products bear risks of the underlying investments, index or reference obligation and are subject to counterparty risk. The Fund may have the right to receive payments only from the structured product, and generally does not have direct rights against the issuer or the entity that sold the assets to be securitized. Certain structured products may be thinly traded or have a limited trading market. In addition to the general risks associated with debt securities discussed herein, structured products carry additional risks, including, but not limited to: the possibility that distributions from collateral securities will not be adequate to make interest or other payments; the quality of the collateral may decline in value or default; and the possibility that the structured products are subordinate to other classes. Structured notes are based upon the movement of one or more factors, including currency exchange rates, interest rates, reference bonds and stock indices, and changes in interest rates and impact of these factors may cause significant price fluctuations. Additionally, changes in the reference instrument or security may cause the interest rate on the structured note to be reduced to zero.
Risk Lose Money [Text]	rr_RiskLoseMoney	You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The Fund has not commenced operations as of the date of this prospectus. The returns presented for the Fund reflect the performance of the Predecessor Fund. It is anticipated that on or about September 17, 2018, the Fund will acquire all of the assets, subject to the liabilities, of the Predecessor Fund through a tax-free reorganization (the “Reorganization”). As a result of the Reorganization, the Fund will adopt the performance and financial history of the Predecessor Fund. The Reorganization is being consummated in connection with a potential reconfiguration of the existing fund complexes overseen by the boards of directors/trustees of the BlackRock-advised funds. The Fund has the same investment objectives, strategies and policies, portfolio management team and contractual arrangements, including the same contractual fees and expenses, as the Predecessor Fund. As a result, the performance of the Fund would have been substantially similar to that of the Predecessor Fund. The information shows you how the Predecessor Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. Class K Shares commenced operations on March 28, 2016, therefore the returns shown in the chart and table prior to the commencement date are those of Institutional Shares, which are not offered in this prospectus. The performance of Class K Shares would be substantially similar to Institutional Shares because Class K Shares and Institutional Shares are invested in the same portfolio of securities and performance would differ only to the extent that Institutional Shares and Class K Shares have different expenses. The actual returns of Class K Shares would have been higher than those of the Institutional Shares because Class K Shares have lower expenses than the Institutional Shares. The table compares the Predecessor Fund’s performance to that of the ICE BofAML 3-Month U.S. Treasury Bill Index. To the extent that dividends and distributions have been paid by the Predecessor Fund, the performance information of the Predecessor Fund in the chart and table assumes reinvestment of the dividends and distributions. As with all such investments, past performance (before and after taxes) is not an indication of future results. The table includes all applicable fees. If BlackRock and its affiliates had not waived or reimbursed certain Predecessor Fund expenses during these periods, the Predecessor Fund’s returns would have been lower. Updated information on the Fund’s performance, including its current net asset value, can be obtained by visiting http://www.blackrock.com or can be obtained by phone at (800) 882-0052.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The information shows you how the Predecessor Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	The Fund has not commenced operations as of the date of this prospectus.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	(800) 882-0052
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	http://www.blackrock.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	As with all such investments, past performance (before and after taxes) is not an indication of future results.
Bar Chart [Heading]	rr_BarChartHeading	Class K Shares ANNUAL TOTAL RETURNS BlackRock Global Long/Short Credit Fund As of 12/31
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	During the periods shown in the bar chart, the highest return for a quarter was 2.48% (quarter ended December 31, 2012) and the lowest return for a quarter was –1.62% (quarter ended September 30, 2015). The year-to-date return as of June 30, 2018 was –0.29%.
Performance Table Heading	rr_PerformanceTableHeading	As of 12/31/17 Average Annual Total Returns
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	Actual after-tax returns depend on the investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
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 the investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Class K | BlackRock Global Long/Short Credit Fund | Class K Shares
Risk/Return:	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.90%	[1],[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Interest Expense	rr_Component1OtherExpensesOverAssets	0.73%
Dividend Expense	rr_Component2OtherExpensesOverAssets	0.04%
Miscellaneous Other Expenses	rr_Component3OtherExpensesOverAssets	0.12%
Other Expenses	rr_OtherExpensesOverAssets	0.89%	[3]
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[3]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.80%
Fee Waivers and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets		[1],[4]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.80%	[1],[4]
1 Year	rr_ExpenseExampleYear01	$ 183
3 Years	rr_ExpenseExampleYear03	566
5 Years	rr_ExpenseExampleYear05	975
10 Years	rr_ExpenseExampleYear10	$ 2,116
2012	rr_AnnualReturn2012	7.07%
2013	rr_AnnualReturn2013	3.74%
2014	rr_AnnualReturn2014	0.92%
2015	rr_AnnualReturn2015	(1.00%)
2016	rr_AnnualReturn2016	3.68%
2017	rr_AnnualReturn2017	3.64%
Year to Date Return, Label	rr_YearToDateReturnLabel	year-to-date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Jun. 30, 2018
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	(0.29%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Dec. 31, 2012
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	2.48%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2015
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(1.62%)
1 Year	rr_AverageAnnualReturnYear01	3.64%
5 Years	rr_AverageAnnualReturnYear05	2.18%
Since Inception	rr_AverageAnnualReturnSinceInception	2.94%
Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 30, 2011
Class K | BlackRock Global Long/Short Credit Fund | Return After Taxes on Distributions | Class K Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	3.10%
5 Years	rr_AverageAnnualReturnYear05	1.10%
Since Inception	rr_AverageAnnualReturnSinceInception	1.96%
Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 30, 2011
Class K | BlackRock Global Long/Short Credit Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class K Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	2.11%
5 Years	rr_AverageAnnualReturnYear05	1.18%
Since Inception	rr_AverageAnnualReturnSinceInception	1.83%
Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 30, 2011
Class K | BlackRock Global Long/Short Credit Fund | ICE BofAML 3-Month U.S. Treasury Bill Index (Reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	0.86%
5 Years	rr_AverageAnnualReturnYear05	0.27%
Since Inception	rr_AverageAnnualReturnSinceInception	0.23%

[1] As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 34, BlackRock Advisors, LLC (“BlackRock”) has contractually agreed to waive the management fee with respect to any portion of the Fund’s assets estimated to be attributable to investments in other equity and fixed-income mutual funds and exchange-traded funds managed by BlackRock or its affiliates that have a contractual management fee, through November 30, 2019. The contractual agreement may be terminated upon 90 days’ notice by a majority of the non-interested trustees of the Trust or by a vote of a majority of the outstanding voting securities of the Fund.

[2] Management Fee is based on the management fee rate of the Predecessor Fund (as defined below).

[3] Other Expenses and Acquired Fund Fees and Expenses are based on estimated amounts for the current fiscal year, which are based on the expenses of the Predecessor Fund for its most recent fiscal year.

[4] As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 34, BlackRock has contractually agreed to waive and/or reimburse fees or expenses in order to limit Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements (excluding Dividend Expense, Interest Expense, Acquired Fund Fees and Expenses and certain other Fund expenses) to 1.15% of average daily net assets through November 30, 2019. The Fund may have to repay some of these waivers and/or reimbursements to BlackRock in the following two years. The contractual agreement may be terminated upon 90 days’ notice by a majority of the non-interested trustees of the Trust or by a vote of a majority of the outstanding voting securities of the Fund.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	BlackRock Funds IV
Prospectus Date	rr_ProspectusDate	Aug. 10, 2018
Document Creation Date	dei_DocumentCreationDate	Aug. 10, 2018