v3.26.1
Shareholder Report
 12 Months Ended
May 31, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSR
Amendment Flag false
Registrant Name T. ROWE PRICE RESERVE INVESTMENT FUNDS, INC.
Entity Central Index Key 0001034386
Entity Investment Company Type N-1A
Document Period End Date May 31, 2026
Shareholder Report Annual or Semi-Annual Annual Shareholder Report
C000005550  
Shareholder Report [Line Items]  
Fund Name Treasury Reserve Fund
No Trading Symbol [Flag] true
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about Treasury Reserve Fund (the "fund") for the period of June 1, 2025 to May 31, 2026.
Additional Information [Text Block] You can find the fund’s prospectus, financial information on Form N‑CSR (which includes required tax information for dividends), holdings, proxy voting information, and other information atwww.troweprice.com/prospectus. You can also request this information without charge by contacting T. Rowe Price at 1‑800‑638‑5660 or info@troweprice.com or contacting your intermediary.
Material Fund Change Notice [Text Block]  
Additional Information Phone Number 1‑800‑638‑5660
Additional Information Email <span style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 13.3333px; font-weight: 400; grid-area: auto; line-height: 17.3333px; margin: 0px; overflow: visible; text-align: justify; text-align-last: left; white-space-collapse: preserve-breaks;">info@troweprice.com</span>
Additional Information Website www.troweprice.com/prospectus
Expenses [Text Block]

What were the fund costs for the last year? (based on a hypothetical $10,000 investment)

Table Summary
 
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Treasury Reserve Fund
$1
0.01%
Expenses Paid, Amount $ 1
Expense Ratio, Percent 0.01%
AssetsNet $ 2,637,485,000
Holdings Count | Holding 41
Advisory Fees Paid, Amount $ 0
Additional Fund Statistics [Text Block]

What are some fund statistics?

Fund Statistics

Table Summary
Total Net Assets (000s)
$2,637,485
Number of Portfolio Holdings
41
Holdings [Text Block]

Security Allocation (as a % of Net Assets)

Table Summary
U.S. Treasury Repurchase Agreement
60.5%
U.S. Treasury Debt
39.7
Short-Term and Other
-0.2
Largest Holdings [Text Block]

Top Ten Holdings (as a % of Net Assets)

Table Summary
U.S. Treasury Bills
21.9%
U.S. Treasury Notes
17.8
BNY Mellon
16.7
Citigroup Global Markets
13.6
Credit Agricole
11.7
State Street
6.9
Royal Bank of Canada
3.2
Wells Fargo
1.9
JPMorgan Chase
1.8
RBC Dominion Securities
1.1
Material Fund Change [Text Block]
Updated Prospectus Web Address www.troweprice.com/paperless