485BPOS

As filed with the U.S. Securities and Exchange Commission on September 11, 2013

Securities Act File No. 333-124463

Investment Company Act File No. 811-21763

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933	x
Pre-Effective Amendment No.	¨
Post-Effective Amendment No. 16	x
and/or REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940	x

Amendment No. 18

(Check appropriate box or boxes)

MANAGED ACCOUNT SERIES

(Exact Name of Registrant as Specified in Charter)

100 Bellevue Parkway

Wilmington, Delaware 19809

(Address of Principal Executive Office)

Registrant’s Telephone Number, including Area Code (800) 441-7762

John M. Perlowski

Managed Account Series

55 East 52^nd Street, New York, New York 10055

(Name and Address of Agent for Service)

Copies to:

Counsel for the Fund: Margery K. Neale, Esq. Willkie Farr & Gallagher LLP 787 Seventh Avenue New York, New York 10019-6099 Benjamin Archibald, Esq. BlackRock Advisors, LLC 55 East 52^nd Street New York, New York 10055

Continuous

(Approximate Date of Proposed Offering)

It is proposed that this filing will become effective:

x immediately upon filing pursuant to paragraph (b)

¨ on (date) pursuant to paragraph (b)

¨ 60 days after filing pursuant to paragraph (a)(1)

¨ on (date) pursuant to paragraph (a)(1)

¨ 75 days after filing pursuant to paragraph (a)(2)

¨ on (date) pursuant to paragraph (a)(2) of Rule 485.

If appropriate, check the following box:

¨ This post-effective amendment designates a new effective date for a previously filed post-effective amendment.

Title of Securities Being Registered: Shares of Beneficial Interest, par value, $0.01 per share.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all the requirements for the effectiveness of this Registration Statement under Rule 485(b) under the Securities Act and it has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of New York, and the State of New York on September 11, 2013.

	Managed Account Series     (Registrant)
By:	/s/ JOHN M. PERLOWSKI
	(John M. Perlowski,
	President and Chief Executive Officer)

Pursuant to the requirements of the Securities Act of 1933, this Post-Effective Amendment to the Registration Statement has been signed below by the following persons in the capacities and on the dates indicated:

Signature	Title	Date
/s/ JOHN M. PERLOWSKI John M. Perlowski	President and Chief Executive Officer     (Principal Executive Officer)	September 11, 2013
/s/ NEAL J. ANDREWS Neal J. Andrews	Chief Financial Officer (Principal     Financial and Accounting Officer)	September 11, 2013
JAMES H. BODURTHA*	Trustee
(James H. Bodurtha)
BRUCE R. BOND*	Trustee
(Bruce R. Bond)
DONALD W. BURTON*	Trustee
(Donald W. Burton)
STUART E. EIZENSTAT*	Trustee
(Stuart E. Eizenstat)
KENNETH A. FROOT*	Trustee
(Kenneth A. Froot)
ROBERT M. HERNANDEZ*	Trustee
(Robert M. Hernandez)

JOHN F. O’BRIEN*	Trustee
(John F. O’Brien)
ROBERTA COOPER RAMO*	Trustee
(Roberta Cooper Ramo)
DAVID H. WALSH*	Trustee
(David H. Walsh)
FRED G. WEISS*	Trustee
(Fred G. Weiss)
PAUL L. AUDET*	Trustee
(Paul L. Audet)
LAURENCE D. FINK*	Trustee
(Laurence D. Fink)
HENRY GABBAY*	Trustee
(Henry Gabbay)

*By:	/s/ BENJAMIN ARCHIBALD	September 11, 2013
	Benjamin Archibald (Attorney-in-Fact)

EXHIBIT INDEX

Index No.	Description of Exhibit
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase

- 5 -

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	Managed Account Series
Prospectus Date	rr_ProspectusDate	Aug. 28, 2013
Document Creation Date	dei_DocumentCreationDate	Aug. 28, 2013

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	Managed Account Series
Prospectus Date	rr_ProspectusDate	Aug. 28, 2013
Global SmallCap Portfolio
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Overview Key Facts About Global SmallCap Portfolio
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The investment objective of the Global SmallCap Portfolio (the “Fund”) is to seek long-term growth of capital.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
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)
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 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. During the most recent fiscal year, the Fund’s portfolio turnover rate was 70% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	70.00%
Expenses Other Expenses Had Extraordinary Expenses Been Included [Text]	rr_ExpensesOtherExpensesHadExtraordinaryExpensesBeenIncluded	Extraordinary expenses may include Dividend Expense, Interest Expense, Acquired Fund Fees and Expenses and certain other Fund expenses.
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 Global SmallCap Portfolio invests in a diversified portfolio primarily consisting of equity securities of small cap issuers in various foreign countries and in the United States. Equity securities consist primarily of common and preferred stocks and depositary receipts, and include securities or other instruments whose price is linked to the value of common stock. Depositary receipts include American Depositary Receipts (“ADRs”), European Depositary Receipts (“EDRs”), Global Depositary Receipts (“GDRs”) and unsponsored depositary receipts. ADRs are receipts typically issued by an American bank or trust company that evidence underlying securities issued by a foreign corporation. EDRs (issued in Europe) and GDRs (issued throughout the world) each evidence a similar ownership arrangement. In addition, the Fund may invest in derivative securities or instruments, such as options and futures, the value of which is based on a common stock or a group of common stocks. The Fund may use derivatives to hedge its investment portfolio against market, interest rate and currency risks or to seek to enhance its return. Under normal circumstances, the Fund invests at least 80% of its assets in equity securities of small cap issuers. Small cap issuers are those whose market capitalization is similar to the market capitalization of companies in the Morgan Stanley Capital International (“MSCI”) World Small Cap IndexSM at the time of the Fund’s investment. As of August 27, 2013, the MSCI World Small Cap IndexSM included companies with free float market capitalizations generally between $15.79 million and $11.48 billion. The market capitalizations of companies in the index change with market conditions and the composition of the MSCI World Small Cap IndexSM. The Fund will invest in securities of issuers from a variety of countries, including those in emerging markets. The Fund may also invest in equity securities issued by emerging growth companies, which are companies of any market capitalization without a long or consistent history of earnings but that Fund management believes have the potential for earnings growth over an extended period of time. The Fund can invest in securities denominated in either U.S. dollars or foreign currencies. 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 (i) of foreign government issuers, (ii) of issuers organized or located outside the United States, (iii) of issuers which primarily trade in a market located outside the United States, or (iv) of 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). For temporary defensive purposes the Fund may deviate very substantially from the allocation described above.
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 principal risks of investing in the Fund. Depositary Receipts Risk — The issuers of unsponsored depositary receipts are not obligated to disclose information that is, in the United States, considered material. Therefore, there may be less information available regarding these issuers and there may not be a correlation between such information and the market value of the depositary receipts. Depositary receipts are generally subject to the same risks as the foreign securities that they evidence or into which they may be converted. Derivatives Risk — The Fund’s use of derivatives may reduce the Fund’s returns and/or increase volatility. 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 perfectly with the overall securities markets. Derivatives are also subject to counterparty risk, which is the risk that the other party in the transaction will not fulfill its contractual obligation. 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 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. Derivatives also may expose the Fund to greater risk and increase its costs. Certain transactions in derivatives involve substantial leverage risk and may expose the Fund to potential losses that exceed the amount originally invested by the Fund. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation is not yet known and may not be known for some time. New regulation may make derivatives more costly, may limit the availability of derivatives, or may otherwise adversely affect the value or performance of derivatives. 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. Equity Securities Risk — Stock markets are volatile. The price of equity securities fluctuates based on changes in a company’s financial condition and overall market and economic conditions. 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 have adversely affected the exchange rate of the Euro and may spread to other countries in Europe, including countries that do not use the Euro. These events may affect the value and liquidity of certain of the Fund’ s investments. 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. Small Cap and Emerging Growth Securities Risk — Small cap or emerging growth companies may have limited product lines or markets. They may be less financially secure than larger, more established companies. They may depend on a more limited management group than larger capitalized companies.
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 information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. The table compares the Fund’s performance to that of the MSCI All Country World Small Cap IndexSM, MSCI World Small Cap IndexSM and MSCI World IndexSM. Effective October 1, 2012, the Fund’s benchmark against which it measured its performance, the MSCI World Small Cap IndexSM, was replaced with the MSCI All Country World Small Cap IndexSM. Fund management believes the MSCI All Country World Small Cap IndexSM more accurately reflects the investment strategy of the Fund. As with all such investments, past performance (before and after taxes) is not an indication of future results. Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown. However, the table includes all applicable fees and sales charges. If the Fund’s investment manager and its affiliates had not waived or reimbursed certain Fund expenses during these periods, the Fund’s returns would have been lower. Updated information on the Fund’s performance can be obtained by phone at (800) 882-0052.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	(800) 882-0052
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	ANNUAL TOTAL RETURNS Global SmallCap Portfolio As of 12/31
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	During the period shown in the bar chart, the highest return for a quarter was 21.00% (quarter ended June 30, 2009) and the lowest return for a quarter was -20.45% (quarter ended December 31, 2008). The year-to-date return as of June 30, 2013 was 11.27%.
Performance Table Heading	rr_PerformanceTableHeading	As of 12/31/12 Average Annual Total Returns
Performance Table Does Reflect Sales Loads	rr_PerformanceTableDoesReflectSalesLoads	However, the table includes all applicable fees and sales charges.
Performance Table Market Index Changed	rr_PerformanceTableMarketIndexChanged	Effective October 1, 2012, the Fund’s benchmark against which it measured its performance, the MSCI World Small Cap IndexSM, was replaced with the MSCI All Country World Small Cap IndexSM. Fund management believes the MSCI All Country World Small Cap IndexSM more accurately reflects the investment strategy of the Fund.
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.
Global SmallCap Portfolio | Global SmallCap Portfolio
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fee	rr_ManagementFeesOverAssets	0.85%	[1]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none	[1]
Other Expenses	rr_OtherExpensesOverAssets	0.22%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.07%	[1]
Fee Waivers and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(1.07%)	[1],[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	none	[1],[2]
1 Year	rr_ExpenseExampleYear01	none
3 Years	rr_ExpenseExampleYear03	none
5 Years	rr_ExpenseExampleYear05	none
10 Years	rr_ExpenseExampleYear10	none
2006	rr_AnnualReturn2006	18.98%
2007	rr_AnnualReturn2007	16.86%
2008	rr_AnnualReturn2008	(36.02%)
2009	rr_AnnualReturn2009	36.96%
2010	rr_AnnualReturn2010	20.48%
2011	rr_AnnualReturn2011	(9.35%)
2012	rr_AnnualReturn2012	18.11%
Year to Date Return, Label	rr_YearToDateReturnLabel	year-to-date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Jun. 30, 2013
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	11.27%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	21.00%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(20.45%)
1 Year	rr_AverageAnnualReturnYear01	18.11%
5 Years	rr_AverageAnnualReturnYear05	2.48%
Since Inception	rr_AverageAnnualReturnSinceInception	7.05%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 02, 2005
Global SmallCap Portfolio | Return After Taxes on Distributions | Global SmallCap Portfolio
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	16.85%
5 Years	rr_AverageAnnualReturnYear05	1.64%
Since Inception	rr_AverageAnnualReturnSinceInception	5.97%
Global SmallCap Portfolio | Return After Taxes on Distributions and Sale of Shares | Global SmallCap Portfolio
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	11.89%
5 Years	rr_AverageAnnualReturnYear05	1.64%
Since Inception	rr_AverageAnnualReturnSinceInception	5.56%
Global SmallCap Portfolio | MSCI All Country World Small Cap Index℠ (Reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	18.06%
5 Years	rr_AverageAnnualReturnYear05	2.33%
Since Inception	rr_AverageAnnualReturnSinceInception	6.00%
Global SmallCap Portfolio | MSCI World Small Cap Index℠ (Reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	17.55%
5 Years	rr_AverageAnnualReturnYear05	2.46%
Since Inception	rr_AverageAnnualReturnSinceInception	4.95%
Global SmallCap Portfolio | MSCI World Index℠ (Reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	15.83%
5 Years	rr_AverageAnnualReturnYear05	(1.18%)
Since Inception	rr_AverageAnnualReturnSinceInception	3.60%

[1] The Fund is an investment option for certain "wrap-fee" or other separately managed account program clients for which BlackRock Investment Management, LLC or certain of its affiliates (individually or collectively referred to as "BIM LLC") receives compensation pursuant to an investment management agreement. Wrap-fee program participants pay a "wrap" fee to the sponsor of the program which typically covers investment advice and transaction costs on trades executed with the sponsor or a designated broker-dealer. You should read carefully the wrap-fee or other program brochure provided to you by your program sponsor or investment adviser. The brochure is required to include information about the fees charged to you and, in the case of a wrap-fee program, the fees paid by the sponsor to BIM LLC. You pay no additional fees or expenses to purchase or redeem shares of the Fund.

[2] As described in the "Management of the Funds" section of the Fund's prospectus on page 27, BlackRock has contractually agreed to waive all fees and pay or reimburse all expenses of the Fund, except extraordinary expenses. Extraordinary expenses may include Dividend Expense, Interest Expense, Acquired Fund Fees and Expenses and certain other Fund expenses.

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Mid Cap Value Opportunities

Fund Overview

Key Facts About Mid Cap Value Opportunities Portfolio

Investment Objective

The investment objective of the Mid Cap Value Opportunities Portfolio (the “Fund”) is to seek capital appreciation and,

secondarily, income.

Fees and Expenses of the Fund

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

Shareholder Fees
(fees paid directly from your investment)

Shareholder Fees	Mid Cap Value Opportunities Mid Cap Value Opportunities Portfolio
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	none
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)	none

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

Annual Fund Operating Expenses		Mid Cap Value Opportunities Mid Cap Value Opportunities Portfolio
Management Fee	[1]	0.65%
Distribution and/or Service (12b-1) Fees	[1]	none
Other Expenses	[1]	0.17%
Total Annual Fund Operating Expenses	[1]	0.82%
Fee Waivers and/or Expense Reimbursements	[1][2]	(0.82%)
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	[1][2]	none

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 (USD $)	1 Year	3 Years	5 Years	10 Years
Mid Cap Value Opportunities Mid Cap Value Opportunities Portfolio	none	none	none	none

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 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. During the most recent fiscal year, the Fund’s portfolio turnover rate was 57% of the average value of its portfolio.

Principal Investment Strategies of the Fund

In seeking to meet its objective, the Mid Cap Value Opportunities Portfolio normally invests at least 80% of its assets in equity securities of mid cap companies. Mid cap companies are companies that at the time of purchase have market capitalizations in the range of companies included in the S&P MidCap 400 Value Index (generally between $488 million and $11.2 billion as of June 28, 2013). This definition of mid-capitalization companies may be changed in response to changes in the market. The Fund purchases securities that Fund management believes have long term potential to grow in size or become more profitable or that the stock market may value more highly in the future. Fund management places particular emphasis on stocks trading at the low end of one or more valuation measures, such as price/book value, or price/sales, price/earnings or price/cash flow ratios. Such companies also may have particular qualities that affect the outlook for such companies, including an attractive market niche. The Fund purchases primarily common stock of U.S. companies in trying to meet its investment objective. The Fund may also invest up to 30% of its total assets in securities issued by foreign companies. The Fund may invest in securities denominated in currencies other than the U.S. dollar.

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 principal risks of investing in the Fund.

• Equity Securities Risk — Stock markets are volatile. The price of equity securities fluctuates based on changes in a company’s financial condition and overall market and economic conditions.

• 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.

• Investment Style Risk — Because different kinds of stocks go in and out of favor depending on market conditions, the Fund’s performance may be better or worse than other funds with different investment styles (e.g., growth vs. value, large cap vs. small cap).

• 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.

• Mid Cap Securities Risk — The securities of mid cap companies generally trade in lower volumes and are generally subject to greater and less predictable price changes than the securities of larger capitalization companies.

Performance Information

The information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. The table compares the Fund’s performance to that of the S&P Mid Cap 400 Value Index. As with all such investments, past performance (before and after taxes) is not an indication of future results. Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown. However, the table includes all applicable fees and sales charges. If the Fund’s investment manager and its affiliates had not waived or reimbursed certain Fund expenses during these periods, the Fund’s returns would have been lower. Updated information on the Fund’s performance can be obtained by phone at 800-882-0052.

ANNUAL TOTAL RETURNS
Mid Cap Value Opportunities Portfolio
As of 12/31

During the period shown in the bar chart, the highest return for a quarter was 19.17% (quarter ended September 30, 2009) and the lowest return for a quarter was -24.72% (quarter ended December 31, 2008). The year-to-date return as of June 30, 2013 was 16.80%.

As of 12/31/12
Average Annual Total Returns

Average Annual Total Returns Mid Cap Value Opportunities	1 Year	5 Years	Since Inception	Inception Date
Mid Cap Value Opportunities Portfolio	14.49%	5.59%	6.99%	Aug. 02, 2005
Mid Cap Value Opportunities Portfolio Return After Taxes on Distributions	14.12%	4.97%	5.67%
Mid Cap Value Opportunities Portfolio Return After Taxes on Distributions and Sale of Shares	9.66%	4.43%	5.28%
S&P MidCap 400 Value Index (Reflects no deduction for fees, expenses or taxes)	18.53%	4.34%	5.29%

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] The Fund is an investment option for certain “wrap-fee” or other separately managed account program clients for which BlackRock Investment Management, LLC or certain of its affiliates (individually or collectively referred to as “BIM LLC”) receives compensation pursuant to an investment management agreement. Wrap-fee program participants pay a “wrap” fee to the sponsor of the program which typically covers investment advice and transaction costs on trades executed with the sponsor or a designated broker-dealer. You should read carefully the wrap-fee or other program brochure provided to you by your program sponsor or investment adviser. The brochure is required to include information about the fees charged to you and, in the case of a wrap-fee program, the fees paid by the sponsor to BIM LLC. You pay no additional fees or expenses to purchase or redeem shares of the Fund.

[2] As described in the "Management of the Funds" section of the Fund's prospectus on page 27, BlackRock has contractually agreed to waive all fees and pay or reimburse all expenses of the Fund, except extraordinary expenses. Extraordinary expenses may include Dividend Expense, Interest Expense, Acquired Fund Fees and Expenses and certain other Fund expenses.

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Global SmallCap Portfolio

Fund Overview

Key Facts About Global SmallCap Portfolio

Investment Objective

The investment objective of the Global SmallCap Portfolio (the “Fund”) is to seek long-term growth of capital.

Fees and Expenses of the Fund

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

Shareholder Fees
(fees paid directly from your investment)

Shareholder Fees	Global SmallCap Portfolio
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	none
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)	none

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

Annual Fund Operating Expenses		Global SmallCap Portfolio
Management Fee	[1]	0.85%
Distribution and/or Service (12b-1) Fees	[1]	none
Other Expenses	[1]	0.22%
Total Annual Fund Operating Expenses	[1]	1.07%
Fee Waivers and/or Expense Reimbursements	[1][2]	(1.07%)
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	[1][2]	none

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 (USD $)	1 Year	3 Years	5 Years	10 Years
Global SmallCap Portfolio	none	none	none	none

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 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. During the most recent fiscal year, the Fund’s portfolio turnover rate was 70% of the average value of its portfolio.

Principal Investment Strategies of the Fund

The Global SmallCap Portfolio invests in a diversified portfolio primarily consisting of equity securities of small cap issuers in various foreign countries and in the United States. Equity securities consist primarily of common and preferred stocks and depositary receipts, and include securities or other instruments whose price is linked to the value of common stock. Depositary receipts include American Depositary Receipts (“ADRs”), European Depositary Receipts (“EDRs”), Global Depositary Receipts (“GDRs”) and unsponsored depositary receipts. ADRs are receipts typically issued by an American bank or trust company that evidence underlying securities issued by a foreign corporation. EDRs (issued in Europe) and GDRs (issued throughout the world) each evidence a similar ownership arrangement. In addition, the Fund may invest in derivative securities or instruments, such as options and futures, the value of which is based on a common stock or a group of common stocks. The Fund may use derivatives to hedge its investment portfolio against market, interest rate and currency risks or to seek to enhance its return.

Under normal circumstances, the Fund invests at least 80% of its assets in equity securities of small cap issuers. Small cap issuers are those whose market capitalization is similar to the market capitalization of companies in the Morgan Stanley Capital International (“MSCI”) World Small Cap Index^SM at the time of the Fund’s investment. As of August 27, 2013, the MSCI World Small Cap Index^SM included companies with free float market capitalizations generally between $15.79 million and $11.48 billion. The market capitalizations of companies in the index change with market conditions and the composition of the MSCI World Small Cap Index^SM.

The Fund will invest in securities of issuers from a variety of countries, including those in emerging markets. The Fund may also invest in equity securities issued by emerging growth companies, which are companies of any market capitalization without a long or consistent history of earnings but that Fund management believes have the potential for earnings growth over an extended period of time. The Fund can invest in securities denominated in either U.S. dollars or foreign currencies.

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 (i) of foreign government issuers, (ii) of issuers organized or located outside the United States, (iii) of issuers which primarily trade in a market located outside the United States, or (iv) of 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). For temporary defensive purposes the Fund may deviate very substantially from the allocation described above.

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 principal risks of investing in the Fund.

• Depositary Receipts Risk — The issuers of unsponsored depositary receipts are not obligated to disclose information that is, in the United States, considered material. Therefore, there may be less information available regarding these issuers and there may not be a correlation between such information and the market value of the depositary receipts. Depositary receipts are generally subject to the same risks as the foreign securities that they evidence or into which they may be converted.

• Derivatives Risk — The Fund’s use of derivatives may reduce the Fund’s returns and/or increase volatility. 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 perfectly with the overall securities markets. Derivatives are also subject to counterparty risk, which is the risk that the other party in the transaction will not fulfill its contractual obligation. 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 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. Derivatives also may expose the Fund to greater risk and increase its costs. Certain transactions in derivatives involve substantial leverage risk and may expose the Fund to potential losses that exceed the amount originally invested by the Fund. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation is not yet known and may not be known for some time. New regulation may make derivatives more costly, may limit the availability of derivatives, or may otherwise adversely affect the value or performance of derivatives.

• 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.

• Equity Securities Risk — Stock markets are volatile. The price of equity securities fluctuates based on changes in a company’s financial condition and overall market and economic conditions.

• 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 have adversely affected the exchange rate of the Euro and may spread to other countries in Europe, including countries that do not use the Euro. These events may affect the value and liquidity of certain of the Fund’ s investments.

• 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.

• Small Cap and Emerging Growth Securities Risk — Small cap or emerging growth companies may have limited product lines or markets. They may be less financially secure than larger, more established companies. They may depend on a more limited management group than larger capitalized companies.

Performance Information

The information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. The table compares the Fund’s performance to that of the MSCI All Country World Small Cap Index^SM, MSCI World Small Cap Index^SM and MSCI World Index^SM. Effective October 1, 2012, the Fund’s benchmark against which it measured its performance, the MSCI World Small Cap Index^SM, was replaced with the MSCI All Country World Small Cap Index^SM. Fund management believes the MSCI All Country World Small Cap Index^SM more accurately reflects the investment strategy of the Fund. As with all such investments, past performance (before and after taxes) is not an indication of future results. Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown. However, the table includes all applicable fees and sales charges. If the Fund’s investment manager and its affiliates had not waived or reimbursed certain Fund expenses during these periods, the Fund’s returns would have been lower. Updated information on the Fund’s performance can be obtained by phone at (800) 882-0052.

ANNUAL TOTAL RETURNS
Global SmallCap Portfolio
As of 12/31

During the period shown in the bar chart, the highest return for a quarter was 21.00% (quarter ended June 30, 2009) and the lowest return for a quarter was -20.45% (quarter ended December 31, 2008). The year-to-date return as of June 30, 2013 was 11.27%.

As of 12/31/12
Average Annual Total Returns

Average Annual Total Returns	1 Year	5 Years	Since Inception	Inception Date
Global SmallCap Portfolio	18.11%	2.48%	7.05%	Aug. 02, 2005
Global SmallCap Portfolio Return After Taxes on Distributions	16.85%	1.64%	5.97%
Global SmallCap Portfolio Return After Taxes on Distributions and Sale of Shares	11.89%	1.64%	5.56%
Global SmallCap Portfolio MSCI All Country World Small Cap Index℠ (Reflects no deduction for fees, expenses or taxes)	18.06%	2.33%	6.00%
Global SmallCap Portfolio MSCI World Small Cap Index℠ (Reflects no deduction for fees, expenses or taxes)	17.55%	2.46%	4.95%
Global SmallCap Portfolio MSCI World Index℠ (Reflects no deduction for fees, expenses or taxes)	15.83%	(1.18%)	3.60%

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] The Fund is an investment option for certain "wrap-fee" or other separately managed account program clients for which BlackRock Investment Management, LLC or certain of its affiliates (individually or collectively referred to as "BIM LLC") receives compensation pursuant to an investment management agreement. Wrap-fee program participants pay a "wrap" fee to the sponsor of the program which typically covers investment advice and transaction costs on trades executed with the sponsor or a designated broker-dealer. You should read carefully the wrap-fee or other program brochure provided to you by your program sponsor or investment adviser. The brochure is required to include information about the fees charged to you and, in the case of a wrap-fee program, the fees paid by the sponsor to BIM LLC. You pay no additional fees or expenses to purchase or redeem shares of the Fund.

[2] As described in the "Management of the Funds" section of the Fund's prospectus on page 27, BlackRock has contractually agreed to waive all fees and pay or reimburse all expenses of the Fund, except extraordinary expenses. Extraordinary expenses may include Dividend Expense, Interest Expense, Acquired Fund Fees and Expenses and certain other Fund expenses.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	Managed Account Series
Prospectus Date	rr_ProspectusDate	Aug. 28, 2013
BlackRock U.S.Mortgage Portfolio
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Overview Key Facts About BlackRock U.S. Mortgage Portfolio
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The investment objective of the BlackRock U.S. Mortgage Portfolio (the “Fund”) is to seek high total return.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the BlackRock-advised fund complex. More information about these and other discounts is available from your financial professional or your selected securities dealer, broker, investment adviser, service provider or industry professional (including BlackRock, The PNC Financial Services Group, Inc. (“PNC”) and their respective affiliates) (each a “Financial Intermediary”) and in the “Details About the Share Classes” section on page 19 of the Fund’s prospectus and in the “Purchase of Shares” section on page II-68 of the Fund’s statement of additional information.
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	September 1, 2014
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 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. During the most recent fiscal year, the Fund’s portfolio turnover rate was 3,166% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	3166.00%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	A contingent deferred sales charge (“CDSC”) of 0.75% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.
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 $25,000 in the BlackRock-advised fund complex.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 25,000
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]	rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees	The Total Annual Fund Operating Expenses do not correlate to the ratio of expenses to average net assets given in the Fund’s most recent annual report, given that the Fund’s most recent annual report does not include Acquired Fund Fees and Expenses.
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:
Expense Example, No Redemption, By Year, Caption [Text]	rr_ExpenseExampleNoRedemptionByYearCaption	You would pay the following expenses if you did not redeem your shares:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies of the Fund
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The BlackRock U.S. Mortgage Portfolio invests primarily in mortgage-related securities. The securities in which the Fund may invest include U.S. government securities, U.S. government agency securities, securities issued by U.S. government instrumentalities and U.S. government-sponsored enterprises, and other mortgage-backed securities or mortgage-related securities issued by the U.S. government or by private issuers. Under normal circumstances, the Fund will invest at least 80% of its assets in mortgage-backed securities and other mortgage-related securities that are issued by issuers located in the United States. The Fund seeks to achieve its investment objective by selecting securities of any maturity issued or guaranteed by the U.S. government, by various agencies of the U.S. government, by various instrumentalities that have been established or sponsored by the U.S. government, or securities issued by banks or other financial institutions. Some of these securities are issued and/or guaranteed by the U.S. government and are supported by the full faith and credit of the United States. Other securities are issued or guaranteed by Federal agencies or government-sponsored enterprises and are not direct obligations of the United States, and are not backed by the full faith and credit of the United States, but involve sponsorship or guarantees by government agencies or enterprises. The Fund may invest in non-agency securities issued by banks and other financial institutions, including non-agency mortgage-related securities. Non-agency securities are not backed by the full faith and credit of the United States and do not involve sponsorship or guarantees by government agencies or enterprises. The Fund may invest a substantial portion of its assets in non-agency mortgage-related securities that are rated below investment grade (commonly known as “junk bonds”). For purposes of determining a bond’s credit rating, split rated bonds will be considered to have the higher credit rating. The Fund may also participate in TBA Transactions and enter into dollar rolls. A TBA Transaction is a method of trading mortgage-backed securities where the buyer and seller agree upon general trade parameters such as agency, settlement date, par amount and price at the time the contract is entered into but the mortgage-backed securities are delivered in the future, generally 30 days later. The actual pools of mortgage-backed securities delivered in a TBA Transaction typically are not determined until two days prior to settlement date. A dollar roll transaction involves a sale by the Fund of a mortgage-backed or other security concurrently with an agreement by the Fund to repurchase a similar security at a later date at an agreed-upon price. The securities that are repurchased will bear the same interest rate and stated maturity as those sold, but pools of mortgages collateralizing those securities may have different prepayment histories than those sold.
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 principal risks of investing in the Fund. Credit Risk — Credit risk refers to the possibility that the issuer of a security 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. Dollar Rolls Risk — Dollar rolls involve the risk that the market value of the securities that the Fund is committed to buy may decline below the price of the securities the Fund has sold. These transactions may involve leverage. 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. In addition, investment in mortgage dollar rolls and participation in TBA Transactions may significantly increase the Fund’s portfolio turnover rate. Interest Rate Risk — Interest rate risk is the risk that prices of fixed-income securities generally increase when interest rates decline and decrease when interest rates increase. Prices of longer-term securities generally change more in response to interest rate changes than prices of shorter-term securities. The Fund may lose money if short- term or long-term interest rates rise sharply or otherwise change in a manner not anticipated by Fund management. Junk Bonds Risk — Although junk bonds generally pay higher rates of interest than investment grade bonds, junk bonds are high risk investments that 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. Liquid investments may become illiquid after purchase by the Fund, particularly during periods of market turmoil. Illiquid investments may be harder to value, especially in changing markets, and if the Fund is forced to sell these investments to meet redemption requests or for other cash needs, the Fund may suffer a loss. 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. 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. Non-Agency Securities Risk — There are no direct or indirect government or agency guarantees of payments in mortgage pools created by non-government issuers. Non-agency securities are also not subject to the same underwriting requirements for the underlying mortgages that are applicable to those mortgage-related securities that have a government or government-sponsored entity guarantee. In addition, a substantial portion of the non-agency securities in which the Fund invests may be rated below investment grade (commonly known as “junk bonds”). Non-agency mortgage-related securities are not traded on an exchange and there may be a limited market for the securities, especially when there is a perceived weakness in the mortgage and real estate market sectors. Without an active trading market, the non-agency mortgage-related securities held in the Fund’s portfolio may be particularly difficult to value because of the complexities involved in assessing the value of the underlying mortgage loans. Prepayment and Extension Risk — When interest rates fall, an issuer may redeem a security with call features by repaying it early, and the Fund may have to invest the proceeds in securities with lower yields. When interest rates rise, certain obligations will be paid off by the issuer more slowly than anticipated, causing the value of these securities to fall.
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 information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. The returns for Institutional Shares are based on the performance of its predecessor class. The returns for Investor A and Investor C Shares prior to December 6, 2010, the commencement of operations of Investor A and Investor C Shares, are based on the performance of the Fund’s Institutional Shares. The returns for Investor A and Investor C Shares, however, are adjusted to reflect the distribution and service (12b-1) fees applicable to Investor A and Investor C Shares, respectively. The table compares the Fund’ s performance to that of the Barclays U.S. Mortgage-Backed Securities Index. As with all such investments, past performance (before and after taxes) is not an indication of future results. Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown. However, the table includes all applicable fees and sales charges. The performance information provided below for periods prior to December 6, 2010 reflects contractual expense waivers or reimbursements that the Fund’s investment manager had in place for the Institutional Shares predecessor class to waive all fees and pay or reimburse all expenses of the Fund, except extraordinary expenses. These contractual waivers or reimbursements have been discontinued for Institutional Shares. If the Fund’s investment manager and its affiliates had not waived or reimbursed certain Fund expenses during these periods, the Fund’s returns would have been lower. Updated information on the Fund’s performance can be obtained by visiting http://www.blackrock.com/funds 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 Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-882-0052
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	http://www.blackrock.com/funds
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	Institutional Shares ANNUAL TOTAL RETURNS BlackRock U.S. Mortgage Portfolio As of 12/31
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	During the period shown in the bar chart, the highest return for a quarter was 5.04% (quarter ended September 30, 2009) and the lowest return for a quarter was -1.66% (quarter ended June 30, 2008). The year-to-date return as of June 30, 2013 was -1.61%.
Performance Table Heading	rr_PerformanceTableHeading	As of 12/31/12 Average Annual Total Returns
Performance Table Does Reflect Sales Loads	rr_PerformanceTableDoesReflectSalesLoads	However, the table includes all applicable fees and sales charges.
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 One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	After-tax returns are shown for Institutional Shares only, and the after-tax returns for Investor A and Investor C Shares will vary.
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. After-tax returns are shown for Institutional Shares only, and the after-tax returns for Investor A and Investor C Shares will vary.
BlackRock U.S.Mortgage Portfolio | Investor A Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	4.00%
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none	[1]
Management Fee	rr_ManagementFeesOverAssets	0.46%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.20%
Interest Expense	rr_Component1OtherExpensesOverAssets	0.02%
Miscellaneous Other Expenses	rr_Component2OtherExpensesOverAssets	0.18%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.92%	[2]
Fee waivers and expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets		[3]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	0.92%	[3]
1 Year	rr_ExpenseExampleYear01	490
3 Years	rr_ExpenseExampleYear03	682
5 Years	rr_ExpenseExampleYear05	889
10 Years	rr_ExpenseExampleYear10	1,486
1 Year	rr_AverageAnnualReturnYear01	3.60%
5 Years	rr_AverageAnnualReturnYear05	6.88%
Since Inception	rr_AverageAnnualReturnSinceInception	6.15%
Inception Date	rr_AverageAnnualReturnInceptionDate	Jul. 29, 2005
BlackRock U.S.Mortgage Portfolio | Investor C Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	1.00%	[4]
Management Fee	rr_ManagementFeesOverAssets	0.46%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.17%
Interest Expense	rr_Component1OtherExpensesOverAssets	0.02%
Miscellaneous Other Expenses	rr_Component2OtherExpensesOverAssets	0.15%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.64%	[2]
Fee waivers and expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets		[3]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.64%	[3]
1 Year	rr_ExpenseExampleYear01	267
3 Years	rr_ExpenseExampleYear03	517
5 Years	rr_ExpenseExampleYear05	892
10 Years	rr_ExpenseExampleYear10	1,944
1 Year	rr_ExpenseExampleNoRedemptionYear01	167
3 Years	rr_ExpenseExampleNoRedemptionYear03	517
5 Years	rr_ExpenseExampleNoRedemptionYear05	892
10 Years	rr_ExpenseExampleNoRedemptionYear10	1,944
1 Year	rr_AverageAnnualReturnYear01	6.22%
5 Years	rr_AverageAnnualReturnYear05	6.97%
Since Inception	rr_AverageAnnualReturnSinceInception	5.96%
Inception Date	rr_AverageAnnualReturnInceptionDate	Jul. 29, 2005
BlackRock U.S.Mortgage Portfolio | Institutional Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fee	rr_ManagementFeesOverAssets	0.46%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.17%
Interest Expense	rr_Component1OtherExpensesOverAssets	0.02%
Miscellaneous Other Expenses	rr_Component2OtherExpensesOverAssets	0.15%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.64%	[2]
Fee waivers and expense reimbursements	rr_FeeWaiverOrReimbursementOverAssets		[3]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	0.64%	[3]
1 Year	rr_ExpenseExampleYear01	65
3 Years	rr_ExpenseExampleYear03	205
5 Years	rr_ExpenseExampleYear05	357
10 Years	rr_ExpenseExampleYear10	$ 798
2006	rr_AnnualReturn2006	5.14%
2007	rr_AnnualReturn2007	6.25%
2008	rr_AnnualReturn2008	1.19%
2009	rr_AnnualReturn2009	14.01%
2010	rr_AnnualReturn2010	12.12%
2011	rr_AnnualReturn2011	5.31%
2012	rr_AnnualReturn2012	8.21%
Year to Date Return, Label	rr_YearToDateReturnLabel	year-to-date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Jun. 30, 2013
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	(1.61%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	5.04%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Jun. 30, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(1.66%)
1 Year	rr_AverageAnnualReturnYear01	8.21%
5 Years	rr_AverageAnnualReturnYear05	8.08%
Since Inception	rr_AverageAnnualReturnSinceInception	7.05%
Inception Date	rr_AverageAnnualReturnInceptionDate	Jul. 29, 2005
BlackRock U.S.Mortgage Portfolio | Return After Taxes on Distributions | Institutional Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	6.31%
5 Years	rr_AverageAnnualReturnYear05	5.53%
Since Inception	rr_AverageAnnualReturnSinceInception	4.74%
BlackRock U.S.Mortgage Portfolio | Return After Taxes on Distributions and Sale of Shares | Institutional Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	5.34%
5 Years	rr_AverageAnnualReturnYear05	5.43%
Since Inception	rr_AverageAnnualReturnSinceInception	4.68%
BlackRock U.S.Mortgage Portfolio | Barclays U.S. Mortgage-Backed Securities Index (Reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	2.59%
5 Years	rr_AverageAnnualReturnYear05	5.67%
Since Inception	rr_AverageAnnualReturnSinceInception	5.58%

[1] A contingent deferred sales charge ("CDSC") of 0.75% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.

[2] The Total Annual Fund Operating Expenses do not correlate to the ratio of expenses to average net assets given in the Fund's most recent annual report, given that the Fund's most recent annual report does not include Acquired Fund Fees and Expenses.

[3] As described in the "Management of the Fund" section of the Fund's prospectus on pages 33 and 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 0.93% of average daily net assets (for Investor A Shares) and 1.68% of average daily net assets (for Investor C Shares) until September 1, 2014. The agreement may be terminated upon 90 days notice by a majority of the non-interested trustees of the Fund or by a vote of a majority of the outstanding voting securities of the Fund.

[4] There is no CDSC on Investor C Shares after one year.

XML

BlackRock U.S.Mortgage Portfolio

Fund Overview

Key Facts About BlackRock U.S. Mortgage Portfolio

Investment Objective

The investment objective of the BlackRock U.S. Mortgage Portfolio (the “Fund”) is to seek high total return.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold 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 $25,000 in the BlackRock-advised fund complex. More information about these and other discounts is available from your financial professional or your selected securities dealer, broker, investment adviser, service provider or industry professional (including BlackRock, The PNC Financial Services Group, Inc. (“PNC”) and their respective affiliates) (each a “Financial Intermediary”) and in the “Details About the Share Classes” section on page 19 of the Fund’s prospectus and in the “Purchase of Shares” section on page II-68 of the Fund’s statement of additional information.

Shareholder Fees
(fees paid directly from your investment)

Shareholder Fees BlackRock U.S.Mortgage Portfolio	Investor A Shares		Investor C Shares		Institutional Shares
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	4.00%		none		none
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)	none	[1]	1.00%	[2]	none

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

Annual Fund Operating Expenses BlackRock U.S.Mortgage Portfolio		Investor A Shares	Investor C Shares	Institutional Shares
Management Fee		0.46%	0.46%	0.46%
Distribution and/or Service (12b-1) Fees		0.25%	1.00%	none
Other Expenses		0.20%	0.17%	0.17%
Interest Expense		0.02%	0.02%	0.02%
Miscellaneous Other Expenses		0.18%	0.15%	0.15%
Acquired Fund Fees and Expenses	[1]	0.01%	0.01%	0.01%
Total Annual Fund Operating Expenses	[1]	0.92%	1.64%	0.64%
Fee waivers and expense reimbursements	[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	[2]	0.92%	1.64%	0.64%

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 BlackRock U.S.Mortgage Portfolio (USD $)	1 Year	3 Years	5 Years	10 Years
Investor A Shares	490	682	889	1,486
Investor C Shares	267	517	892	1,944
Institutional Shares	65	205	357	798

You would pay the following expenses if you did not redeem your shares:

Expense Example, No Redemption (USD $)	1 Year	3 Years	5 Years	10 Years
BlackRock U.S.Mortgage Portfolio Investor C Shares	167	517	892	1,944

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 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. During the most recent fiscal year, the Fund’s portfolio turnover rate was 3,166% of the average value of its portfolio.

Principal Investment Strategies of the Fund

The BlackRock U.S. Mortgage Portfolio invests primarily in mortgage-related securities. The securities in which the Fund may invest include U.S. government securities, U.S. government agency securities, securities issued by U.S. government instrumentalities and U.S. government-sponsored enterprises, and other mortgage-backed securities or mortgage-related securities issued by the U.S. government or by private issuers. Under normal circumstances, the Fund will invest at least 80% of its assets in mortgage-backed securities and other mortgage-related securities that are issued by issuers located in the United States.

The Fund seeks to achieve its investment objective by selecting securities of any maturity issued or guaranteed by the U.S. government, by various agencies of the U.S. government, by various instrumentalities that have been established or sponsored by the U.S. government, or securities issued by banks or other financial institutions. Some of these securities are issued and/or guaranteed by the U.S. government and are supported by the full faith and credit of the United States. Other securities are issued or guaranteed by Federal agencies or government-sponsored enterprises and are not direct obligations of the United States, and are not backed by the full faith and credit of the United States, but involve sponsorship or guarantees by government agencies or enterprises.

The Fund may invest in non-agency securities issued by banks and other financial institutions, including non-agency mortgage-related securities. Non-agency securities are not backed by the full faith and credit of the United States and do not involve sponsorship or guarantees by government agencies or enterprises. The Fund may invest a substantial portion of its assets in non-agency mortgage-related securities that are rated below investment grade (commonly known as “junk bonds”). For purposes of determining a bond’s credit rating, split rated bonds will be considered to have the higher credit rating.

The Fund may also participate in TBA Transactions and enter into dollar rolls. A TBA Transaction is a method of trading mortgage-backed securities where the buyer and seller agree upon general trade parameters such as agency, settlement date, par amount and price at the time the contract is entered into but the mortgage-backed securities are delivered in the future, generally 30 days later. The actual pools of mortgage-backed securities delivered in a TBA Transaction typically are not determined until two days prior to settlement date. A dollar roll transaction involves a sale by the Fund of a mortgage-backed or other security concurrently with an agreement by the Fund to repurchase a similar security at a later date at an agreed-upon price. The securities that are repurchased will bear the same interest rate and stated maturity as those sold, but pools of mortgages collateralizing those securities may have different prepayment histories than those sold.

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 principal risks of investing in the Fund.

• Credit Risk — Credit risk refers to the possibility that the issuer of a security 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.

• Dollar Rolls Risk — Dollar rolls involve the risk that the market value of the securities that the Fund is committed to buy may decline below the price of the securities the Fund has sold. These transactions may involve leverage.

• 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. In addition, investment in mortgage dollar rolls and participation in TBA Transactions may significantly increase the Fund’s portfolio turnover rate.

• Interest Rate Risk — Interest rate risk is the risk that prices of fixed-income securities generally increase when interest rates decline and decrease when interest rates increase. Prices of longer-term securities generally change more in response to interest rate changes than prices of shorter-term securities. The Fund may lose money if short- term or long-term interest rates rise sharply or otherwise change in a manner not anticipated by Fund management.

• Junk Bonds Risk — Although junk bonds generally pay higher rates of interest than investment grade bonds, junk bonds are high risk investments that 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. Liquid investments may become illiquid after purchase by the Fund, particularly during periods of market turmoil. Illiquid investments may be harder to value, especially in changing markets, and if the Fund is forced to sell these investments to meet redemption requests or for other cash needs, the Fund may suffer a loss. 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.

• 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.

• Non-Agency Securities Risk — There are no direct or indirect government or agency guarantees of payments in mortgage pools created by non-government issuers. Non-agency securities are also not subject to the same underwriting requirements for the underlying mortgages that are applicable to those mortgage-related securities that have a government or government-sponsored entity guarantee. In addition, a substantial portion of the non-agency securities in which the Fund invests may be rated below investment grade (commonly known as “junk bonds”).
  
  Non-agency mortgage-related securities are not traded on an exchange and there may be a limited market for the securities, especially when there is a perceived weakness in the mortgage and real estate market sectors. Without an active trading market, the non-agency mortgage-related securities held in the Fund’s portfolio may be particularly difficult to value because of the complexities involved in assessing the value of the underlying mortgage loans.

• Prepayment and Extension Risk — When interest rates fall, an issuer may redeem a security with call features by repaying it early, and the Fund may have to invest the proceeds in securities with lower yields. When interest rates rise, certain obligations will be paid off by the issuer more slowly than anticipated, causing the value of these securities to fall.

Performance Information

The information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. The returns for Institutional Shares are based on the performance of its predecessor class. The returns for Investor A and Investor C Shares prior to December 6, 2010, the commencement of operations of Investor A and Investor C Shares, are based on the performance of the Fund’s Institutional Shares. The returns for Investor A and Investor C Shares, however, are adjusted to reflect the distribution and service (12b-1) fees applicable to Investor A and Investor C Shares, respectively. The table compares the Fund’ s performance to that of the Barclays U.S. Mortgage-Backed Securities Index. As with all such investments, past performance (before and after taxes) is not an indication of future results. Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown. However, the table includes all applicable fees and sales charges. The performance information provided below for periods prior to December 6, 2010 reflects contractual expense waivers or reimbursements that the Fund’s investment manager had in place for the Institutional Shares predecessor class to waive all fees and pay or reimburse all expenses of the Fund, except extraordinary expenses. These contractual waivers or reimbursements have been discontinued for Institutional Shares. If the Fund’s investment manager and its affiliates had not waived or reimbursed certain Fund expenses during these periods, the Fund’s returns would have been lower. Updated information on the Fund’s performance can be obtained by visiting http://www.blackrock.com/funds or can be obtained by phone at 800-882-0052.

Institutional Shares
ANNUAL TOTAL RETURNS
BlackRock U.S. Mortgage Portfolio
As of 12/31

During the period shown in the bar chart, the highest return for a quarter was 5.04% (quarter ended September 30, 2009) and the lowest return for a quarter was -1.66% (quarter ended June 30, 2008). The year-to-date return as of June 30, 2013 was -1.61%.

As of 12/31/12
Average Annual Total Returns

Average Annual Total Returns BlackRock U.S.Mortgage Portfolio	1 Year	5 Years	Since Inception	Inception Date
Institutional	8.21%	8.08%	7.05%	Jul. 29, 2005
Institutional Return After Taxes on Distributions	6.31%	5.53%	4.74%
Institutional Return After Taxes on Distributions and Sale of Shares	5.34%	5.43%	4.68%
Investor A	3.60%	6.88%	6.15%	Jul. 29, 2005
Investor C	6.22%	6.97%	5.96%	Jul. 29, 2005
Barclays U.S. Mortgage-Backed Securities Index (Reflects no deduction for fees, expenses or taxes)	2.59%	5.67%	5.58%

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. After-tax returns are shown for Institutional Shares only, and the after-tax returns for Investor A and Investor C Shares will vary.

[1] A contingent deferred sales charge ("CDSC") of 0.75% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.

[2] There is no CDSC on Investor C Shares after one year.

[1] The Total Annual Fund Operating Expenses do not correlate to the ratio of expenses to average net assets given in the Fund's most recent annual report, given that the Fund's most recent annual report does not include Acquired Fund Fees and Expenses.

[2] As described in the "Management of the Fund" section of the Fund's prospectus on pages 33 and 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 0.93% of average daily net assets (for Investor A Shares) and 1.68% of average daily net assets (for Investor C Shares) until September 1, 2014. The agreement may be terminated upon 90 days notice by a majority of the non-interested trustees of the Fund 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	Managed Account Series
Prospectus Date	rr_ProspectusDate	Aug. 28, 2013
Mid Cap Value Opportunities
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Overview Key Facts About Mid Cap Value Opportunities Portfolio
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The investment objective of the Mid Cap Value Opportunities Portfolio (the “Fund”) is to seek capital appreciation and,
Objective, Secondary [Text Block]	rr_ObjectiveSecondaryTextBlock	secondarily, income.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
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)
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 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. During the most recent fiscal year, the Fund’s portfolio turnover rate was 57% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	57.00%
Expenses Other Expenses Had Extraordinary Expenses Been Included [Text]	rr_ExpensesOtherExpensesHadExtraordinaryExpensesBeenIncluded	Extraordinary expenses may include Dividend Expense, Interest Expense, Acquired Fund Fees and Expenses and certain other Fund expenses.
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	In seeking to meet its objective, the Mid Cap Value Opportunities Portfolio normally invests at least 80% of its assets in equity securities of mid cap companies. Mid cap companies are companies that at the time of purchase have market capitalizations in the range of companies included in the S&P MidCap 400 Value Index (generally between $488 million and $11.2 billion as of June 28, 2013). This definition of mid-capitalization companies may be changed in response to changes in the market. The Fund purchases securities that Fund management believes have long term potential to grow in size or become more profitable or that the stock market may value more highly in the future. Fund management places particular emphasis on stocks trading at the low end of one or more valuation measures, such as price/book value, or price/sales, price/earnings or price/cash flow ratios. Such companies also may have particular qualities that affect the outlook for such companies, including an attractive market niche. The Fund purchases primarily common stock of U.S. companies in trying to meet its investment objective. The Fund may also invest up to 30% of its total assets in securities issued by foreign companies. The Fund may invest in securities denominated in currencies other than the U.S. dollar.
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 principal risks of investing in the Fund. Equity Securities Risk — Stock markets are volatile. The price of equity securities fluctuates based on changes in a company’s financial condition and overall market and economic conditions. 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. Investment Style Risk — Because different kinds of stocks go in and out of favor depending on market conditions, the Fund’s performance may be better or worse than other funds with different investment styles (e.g., growth vs. value, large cap vs. small cap). 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. Mid Cap Securities Risk — The securities of mid cap companies generally trade in lower volumes and are generally subject to greater and less predictable price changes than the securities of larger capitalization companies.
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 information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. The table compares the Fund’s performance to that of the S&P Mid Cap 400 Value Index. As with all such investments, past performance (before and after taxes) is not an indication of future results. Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown. However, the table includes all applicable fees and sales charges. If the Fund’s investment manager and its affiliates had not waived or reimbursed certain Fund expenses during these periods, the Fund’s returns would have been lower. Updated information on the Fund’s performance can be obtained by phone at 800-882-0052.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-882-0052
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	ANNUAL TOTAL RETURNS Mid Cap Value Opportunities Portfolio As of 12/31
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	During the period shown in the bar chart, the highest return for a quarter was 19.17% (quarter ended September 30, 2009) and the lowest return for a quarter was -24.72% (quarter ended December 31, 2008). The year-to-date return as of June 30, 2013 was 16.80%.
Performance Table Heading	rr_PerformanceTableHeading	As of 12/31/12 Average Annual Total Returns
Performance Table Does Reflect Sales Loads	rr_PerformanceTableDoesReflectSalesLoads	However, the table includes all applicable fees and sales charges.
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.
Mid Cap Value Opportunities | Mid Cap Value Opportunities Portfolio
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fee	rr_ManagementFeesOverAssets	0.65%	[1]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none	[1]
Other Expenses	rr_OtherExpensesOverAssets	0.17%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.82%	[1]
Fee Waivers and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.82%)	[1],[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	none	[1],[2]
1 Year	rr_ExpenseExampleYear01	none
3 Years	rr_ExpenseExampleYear03	none
5 Years	rr_ExpenseExampleYear05	none
10 Years	rr_ExpenseExampleYear10	none
2006	rr_AnnualReturn2006	14.30%
2007	rr_AnnualReturn2007	4.69%
2008	rr_AnnualReturn2008	(35.28%)
2009	rr_AnnualReturn2009	37.86%
2010	rr_AnnualReturn2010	27.50%
2011	rr_AnnualReturn2011	0.79%
2012	rr_AnnualReturn2012	14.49%
Year to Date Return, Label	rr_YearToDateReturnLabel	year-to-date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Jun. 30, 2013
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	16.80%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	19.17%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(24.72%)
1 Year	rr_AverageAnnualReturnYear01	14.49%
5 Years	rr_AverageAnnualReturnYear05	5.59%
Since Inception	rr_AverageAnnualReturnSinceInception	6.99%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 02, 2005
Mid Cap Value Opportunities | Return After Taxes on Distributions | Mid Cap Value Opportunities Portfolio
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	14.12%
5 Years	rr_AverageAnnualReturnYear05	4.97%
Since Inception	rr_AverageAnnualReturnSinceInception	5.67%
Mid Cap Value Opportunities | Return After Taxes on Distributions and Sale of Shares | Mid Cap Value Opportunities Portfolio
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	9.66%
5 Years	rr_AverageAnnualReturnYear05	4.43%
Since Inception	rr_AverageAnnualReturnSinceInception	5.28%
Mid Cap Value Opportunities | S&P MidCap 400 Value Index (Reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	18.53%
5 Years	rr_AverageAnnualReturnYear05	4.34%
Since Inception	rr_AverageAnnualReturnSinceInception	5.29%

[1] The Fund is an investment option for certain “wrap-fee” or other separately managed account program clients for which BlackRock Investment Management, LLC or certain of its affiliates (individually or collectively referred to as “BIM LLC”) receives compensation pursuant to an investment management agreement. Wrap-fee program participants pay a “wrap” fee to the sponsor of the program which typically covers investment advice and transaction costs on trades executed with the sponsor or a designated broker-dealer. You should read carefully the wrap-fee or other program brochure provided to you by your program sponsor or investment adviser. The brochure is required to include information about the fees charged to you and, in the case of a wrap-fee program, the fees paid by the sponsor to BIM LLC. You pay no additional fees or expenses to purchase or redeem shares of the Fund.

[2] As described in the "Management of the Funds" section of the Fund's prospectus on page 27, BlackRock has contractually agreed to waive all fees and pay or reimburse all expenses of the Fund, except extraordinary expenses. Extraordinary expenses may include Dividend Expense, Interest Expense, Acquired Fund Fees and Expenses and certain other Fund expenses.

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Document and Entity Information	12 Months Ended
	Aug. 28, 2013
Risk/Return:
Document Type	485BPOS
Document Period End Date	Apr. 30, 2013
Registrant Name	Managed Account Series
Central Index Key	0001323737
Amendment Flag	false
Document Creation Date	Aug. 28, 2013
Document Effective Date	Aug. 28, 2013
Prospectus Date	Aug. 28, 2013