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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName T. Rowe Price Prime Reserve Fund, Inc.
Prospectus Date rr_ProspectusDate Oct. 01, 2012
T. Rowe Price Prime Reserve Fund, Inc.
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading
T. Rowe Price

Prime Reserve Fund

SUMMARY
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The fund’s goals are preservation of capital, liquidity, and, consistent with these, the highest possible current income.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
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 Fees and Expenses of the Fund

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)
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 Investments, Risks, and Performance

Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock The fund is a money fund managed in compliance with Rule 2a-7 under the Investment Company Act of 1940. The fund is managed to provide a stable share price of $1.00 by investing in high-quality U.S. dollar-denominated money market securities. The fund’s weighted average maturity will not exceed 60 days, the fund’s weighted average life will not exceed 120 days, and the fund will not purchase any security with a remaining maturity longer than 397 calendar days (unless otherwise permitted by Rule 2a-7). When calculating its weighted average maturity, the fund may shorten its maturity by using the interest rate resets of certain adjustable rate securities. The fund may not take into account these resets when calculating its weighted average life.

The fund buys securities within the two highest short-term rating categories assigned by established credit rating agencies or, if unrated, deemed to be of comparable quality by T. Rowe Price. All securities purchased by the fund present minimal credit risk in the opinion of T. Rowe Price. In selecting securities for the fund, the portfolio manager may examine relationships among yields of various types and maturities of money market securities in the context of interest rate outlooks. The fund’s yield will fluctuate with changes in short-term interest rates.

The fund may invest in municipal money market securities issued by state and local governments as well as money market securities issued by foreign companies and financial institutions, which include U.S. dollar-denominated money market securities traded outside of the U.S. and U.S. dollar-denominated money market securities of foreign issuers traded in the U.S.

The fund may sell holdings for a variety of reasons, such as to adjust the portfolio’s average maturity or to shift assets into and out of higher-yielding securities.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock As with any mutual fund, there can be no guarantee the fund will achieve its objective. Although the fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the fund. An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Money funds have experienced significant pressures from shareholder redemptions, issuer credit downgrades, illiquid markets, and historically low yields on the securities they can hold. There have been a very small number of money funds in other fund complexes that have “broken the buck,” which means that those funds’ investors did not receive $1.00 per share for their investment in those funds. You should be aware that the fund’s investment adviser is under no obligation to provide financial support to the fund or take other measures to ensure that you receive $1.00 per share for your investment in the fund. The potential for realizing a loss of principal in the fund could derive from:

Credit risk This is the risk that an issuer of a debt security could suffer an adverse change in financial condition that results in a payment default, security downgrade, or inability to meet a financial obligation. Rule 2a-7 under the Investment Company Act of 1940 requires that money funds invest in securities rated in the two highest short-term credit rating categories. However, the credit quality of the securities held by the fund may change rapidly in certain market environments.

Interest rate risk This is the risk that a decline in interest rates will lower a fund’s yield, or that a rise in the overall level of interest rates will cause a decline in the prices of fixed income securities held by a fund. The fund’s yield will vary; it is not fixed for a specific period like the yield on a bank certificate of deposit. This is a disadvantage when interest rates are falling because the fund would have to reinvest at lower interest rates. During periods of extremely low or negative short-term interest rates, the fund may not be able to maintain a positive yield or yields on par with historical levels. In addition, the adoption of more stringent regulations governing the management of money funds could have a negative effect on the fund’s yield. Finally, the fund’s investment adviser may discontinue its voluntary waiver of the fund’s management fee at any time, which could also negatively affect the fund’s yield.

Liquidity risk This is the risk that the fund may not be able to sell a holding in a timely manner at a desired price. The fund may experience heavy redemptions, particularly during periods of declining or illiquid markets, which could cause the fund to liquidate its assets at inopportune times or at a depressed value and affect the fund’s ability to maintain a $1.00 share price. In addition, the fund may suspend redemptions when permitted by applicable regulations.

Municipal securities risk This is the risk that the fund’s investments in municipal securities may be adversely affected by changes in the financial condition of certain municipal securities issuers and the economy, as well as by events such as unfavorable legislative or political developments that impact the overall municipal securities markets or certain sectors of the municipal securities market. The secondary market for certain municipal securities tends to be less developed and liquid than many other securities markets.

Foreign investing risk This is the risk that the fund’s investments in foreign securities may be adversely affected by political and economic conditions overseas, reduced liquidity, or differences in settlement and regulatory standards.
Risk Lose Money [Text] rr_RiskLoseMoney Although the fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the fund.
Risk Money Market Fund [Text] rr_RiskMoneyMarketFund Although the fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the fund. An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The bar chart showing calendar year returns and the average annual total returns table indicate risk by illustrating how much returns can differ from one year to the next. The fund’s past performance is not necessarily an indication of future performance.

The fund can also experience short-term performance swings, as shown by the best and worst calendar quarter returns during the years depicted.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart showing calendar year returns and the average annual total returns table indicate risk by illustrating how much returns can differ from one year to the next.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-225-5132
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress troweprice.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The fund’s past performance is not necessarily an indication of future performance.
Bar Chart [Heading] rr_BarChartHeading
Prime Reserve Fund
Calendar Year Returns
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
      Quarter
Ended		       Total
Return
Best Quarter      9/30/07      1.23%
Worst Quarter      12/31/11         0.00%

The fund’s return for the six months ended 6/30/12 was 0.01%.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns

Periods ended
December 31, 2011
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock Updated performance information is available through troweprice.com or may be obtained by calling 1-800-225-5132.
T. Rowe Price Prime Reserve Fund, Inc. | T. Rowe Price Prime Reserve Fund, Inc.
  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Redemption fee rr_RedemptionFeeOverRedemption none
Maximum account fee rr_MaximumAccountFee 20 [1]
Management fees rr_ManagementFeesOverAssets 0.35%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 0.56% [2]
1 year rr_ExpenseExampleYear01 57
3 years rr_ExpenseExampleYear03 179
5 years rr_ExpenseExampleYear05 313
10 years rr_ExpenseExampleYear10 701
2002 rr_AnnualReturn2002 1.39%
2003 rr_AnnualReturn2003 0.60%
2004 rr_AnnualReturn2004 0.81%
2005 rr_AnnualReturn2005 2.71%
2006 rr_AnnualReturn2006 4.56%
2007 rr_AnnualReturn2007 4.87%
2008 rr_AnnualReturn2008 2.55%
2009 rr_AnnualReturn2009 0.19%
2010 rr_AnnualReturn2010 0.01%
2011 rr_AnnualReturn2011 0.01%
Year to Date Return, Label rr_YearToDateReturnLabel The fund's return for the six months ended
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Jun. 30, 2012
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 0.01%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2007
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 1.23%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn 0.00%
1 Year rr_AverageAnnualReturnYear01 0.01%
5 Years rr_AverageAnnualReturnYear05 1.51%
10 Years rr_AverageAnnualReturnYear10 1.76%
T. Rowe Price Prime Reserve Fund, Inc. | Lipper Money Market Funds Average
  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 0.02%
5 Years rr_AverageAnnualReturnYear05 1.36%
10 Years rr_AverageAnnualReturnYear10 1.56%
[1] Subject to certain exceptions, accounts with a balance of less than $10,000 are charged an annual $20 fee.
[2] The figure shown under "Total annual fund operating expenses" does not match the "Ratio of expenses to average net assets" shown in the Financial Highlights table, as that figure includes the effect of voluntary management fee waivers.