| N-2 - USD ($) $ / shares in Units, $ in Thousands | 6 Months Ended | |||||||||||||
| Apr. 30, 2024 | Oct. 31, 2023 | Oct. 31, 2022 | Apr. 30, 2024 | Oct. 31, 2021 | Oct. 31, 2020 | Oct. 31, 2019 | Oct. 31, 2018 | Oct. 31, 2017 | Oct. 31, 2016 | Oct. 31, 2015 | Oct. 31, 2014 | Oct. 31, 2013 | ||
| Cover [Abstract] | ||||||||||||||
| Entity Central Index Key | 0001263994 | |||||||||||||
| Amendment Flag | false | |||||||||||||
| Document Type | N-CSRS | |||||||||||||
| Entity Registrant Name | Reaves Utility Income Fund | |||||||||||||
| Capital Stock, Long-Term Debt, and Other Securities [Abstract] | ||||||||||||||
| Capital Stock [Table Text Block] | NOTE 4. CAPITAL TRANSACTIONS Common Shares: There are an unlimited number of no par value common shares of beneficial interest authorized. The Fund has a registration statement on file with the SEC (the “Shelf Registration Statement”), pursuant to which the Fund may offer common shares, from time to time, in one or more offerings, up to a maximum aggregate offering price of $600,000,000 on terms to be determined at the time of the offering. On September 19, 2022, the Fund entered into a distribution agreement (the “Distribution Agreement”) with Paralel Distributors LLC (“Paralel Distributors”), pursuant to which the Fund may offer and sell up to 8,000,000 of the Fund’s common shares from time to time through Paralel Distributors and a sub-placement agent in transactions deemed to be “at the market” as defined in Rule 415 under the Securities Act of 1933, as amended. The Distribution Agreement was amended on February 6, 2024, which increased the number of common shares that may be offered to 16,065,000. During the period ended April 30, 2024, 4,260,902 common shares under the Distribution Agreement were sold totaling $110,765,238 in proceeds to the Fund, net of offering costs of $12,328. For the shares sold during the period ended April 30, 2024 pursuant to the Distribution Agreement, commissions totaling $1,118,974 were paid, of which $223,795 was retained by Paralel Distributors with the remainder paid to a sub-placement agent. Offering costs paid as a result of the Fund’s Shelf Registration Statement but not yet incurred as of April 30, 2024 are approximately $11,522. Transactions in common shares were as follows: Period Ended April 30, 2024 Year Ended October 31, 2023 Common Shares outstanding - beginning of period 77,203,272 71,977,353 Common Shares issued from sale of shares 4,260,902 4,937,304 Common Shares issued as reinvestment of dividends 168,306 288,615 Common Shares outstanding - end of period 81,632,480 77,203,272 | |||||||||||||
| Document Period End Date | Apr. 30, 2024 | |||||||||||||
| Borrowings Outstanding [Member] | ||||||||||||||
| Financial Highlights [Abstract] | ||||||||||||||
| Senior Securities Amount | $ 545,000 | $ 520,000 | $ 500,000 | $ 545,000 | $ 450,000 | $ 345,000 | $ 445,000 | $ 445,000 | $ 320,000 | $ 320,000 | $ 320,000 | $ 290,000 | ||
| Senior Securities Coverage per Unit | [1] | $ 4,908 | $ 4,642 | $ 4,989 | $ 4,908 | $ 5,796 | $ 5,811 | $ 5,000 | $ 4,472 | $ 6,040 | $ 4,489 | $ 3,747 | $ 4,273 | |
| Common Shares [Member] | ||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||
| Share Price | 26.26 | 24.56 | 27.62 | 26.26 | 33.96 | 31.45 | 37.09 | 30.36 | 31.02 | 30 | 29.67 | 30.88 | ||
| NAV Per Share | $ 26.09 | $ 24.53 | $ 27.71 | $ 26.09 | $ 33.09 | $ 30.77 | $ 36.52 | $ 31.74 | $ 33.14 | $ 32.53 | $ 30.29 | $ 32.71 | $ 27.91 | |
| Capital Stock, Long-Term Debt, and Other Securities [Abstract] | ||||||||||||||
| Outstanding Security, Not Held [Shares] | 81,632,480 | 77,203,272 | 71,977,353 | |||||||||||
| [1]Calculated by subtracting the Fund’s total liabilities (excluding the principal amount of Leverage Facility) from the Fund’s total assets and dividing by the principal amount of the Leverage Facility and then multiplying by $1,000. | ||||||||||||||
