| Form N-CSR Cover | 6 Months Ended |
| Nov. 30, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | T. ROWE PRICE GNMA FUND, INC. |
| Entity Central Index Key | 0000779785 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Nov. 30, 2024 |
| Shareholder Report | 6 Months Ended |
| Nov. 30, 2024 USD ($) Holding | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | T. ROWE PRICE GNMA FUND, INC. |
| Entity Central Index Key | 0000779785 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Nov. 30, 2024 |
| C000005523 | |
| Shareholder Report [Line Items] | |
| Fund Name | GNMA Fund |
| Class Name | Investor Class |
| Trading Symbol | PRGMX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about GNMA Fund (the "fund") for the period of June 1, 2024 to November 30, 2024. 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 at www.troweprice.com/prospectus info troweprice.com |
| Shareholder Report Annual or Semi-Annual | Semi-Annual Shareholder Report |
| 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 at www.troweprice.com/prospectus info troweprice.com |
| Material Fund Change Notice [Text Block] | |
| Additional Information Phone Number | 1‑800‑638‑5660 |
| Additional Information Email | info@troweprice.com</span>" id="sjs-B20"><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;">info@troweprice.com</span> |
| Additional Information Website | www.troweprice.com/prospectus |
| Expenses [Text Block] | What were the fund costs for the last six months? Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment GNMA Fund - Investor Class $32 0.62% |
| Expenses Paid, Amount | $ 32 |
| Expense Ratio, Percent | 0.62% |
| AssetsNet | $ 993,091,000 |
| Holdings Count | Holding | 770 |
| InvestmentCompanyPortfolioTurnover | 119.60% |
| Additional Fund Statistics Significance or Limits [Text Block] | What are some fund statistics? Fund Statistics Total Net Assets (000s) $993,091 Number of Portfolio Holdings 770 |
| Holdings [Text Block] | AAA Rated 1.1 % U.S. Government Agency Securities 102.3 Reserves - |
| Largest Holdings [Text Block] | Government National Mortgage Assn. 93.4 % Federal National Mortgage Assn. 6.6 Federal Home Loan Mortgage 2.3 Tricon Residential Trust 0.3 Sequoia Mortgage Trust 0.2 Tricon American Homes Trust 0.2 OBX Trust 0.2 Arroyo Mortgage Trust 0.1 Finance of America HECM Buyout 0.1 Morgan Stanley Residential Mortgage Loan Trust 0.1 |
| Material Fund Change [Text Block] | |
| Updated Prospectus Web Address | www.troweprice.com/paperless |
| C000190558 | |
| Shareholder Report [Line Items] | |
| Fund Name | GNMA Fund |
| Class Name | I Class |
| Trading Symbol | PRXAX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about GNMA Fund (the "fund") for the period of June 1, 2024 to November 30, 2024. 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 at www.troweprice.com/prospectus info troweprice.com |
| Shareholder Report Annual or Semi-Annual | Semi-Annual Shareholder Report |
| 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 at www.troweprice.com/prospectus info troweprice.com |
| Material Fund Change Notice [Text Block] | |
| Additional Information Phone Number | 1‑800‑638‑5660 |
| Additional Information Email | info@troweprice.com</span>" id="sjs-B43"><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;">info@troweprice.com</span> |
| Additional Information Website | www.troweprice.com/prospectus |
| Expenses [Text Block] | What were the fund costs for the last six months? Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment GNMA Fund - I Class $21 0.40% |
| Expenses Paid, Amount | $ 21 |
| Expense Ratio, Percent | 0.40% |
| AssetsNet | $ 993,091,000 |
| Holdings Count | Holding | 770 |
| InvestmentCompanyPortfolioTurnover | 119.60% |
| Additional Fund Statistics Significance or Limits [Text Block] | What are some fund statistics? Fund Statistics Total Net Assets (000s) $993,091 Number of Portfolio Holdings 770 |
| Holdings [Text Block] | AAA Rated 1.1 % U.S. Government Agency Securities 102.3 Reserves - |
| Largest Holdings [Text Block] | Government National Mortgage Assn. 93.4 % Federal National Mortgage Assn. 6.6 Federal Home Loan Mortgage 2.3 Tricon Residential Trust 0.3 Sequoia Mortgage Trust 0.2 Tricon American Homes Trust 0.2 OBX Trust 0.2 Arroyo Mortgage Trust 0.1 Finance of America HECM Buyout 0.1 Morgan Stanley Residential Mortgage Loan Trust 0.1 |
| Material Fund Change [Text Block] | |
| Updated Prospectus Web Address | www.troweprice.com/paperless |
| C000225814 | |
| Shareholder Report [Line Items] | |
| Fund Name | GNMA Fund |
| Class Name | Z Class |
| Trading Symbol | TRZGX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about GNMA Fund (the "fund") for the period of June 1, 2024 to November 30, 2024. 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 at www.troweprice.com/prospectus info troweprice.com |
| Shareholder Report Annual or Semi-Annual | Semi-Annual Shareholder Report |
| 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 at www.troweprice.com/prospectus info troweprice.com |
| Material Fund Change Notice [Text Block] | |
| Additional Information Phone Number | 1‑800‑638‑5660 |
| Additional Information Email | info@troweprice.com</span>" id="sjs-B66"><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;">info@troweprice.com</span> |
| Additional Information Website | www.troweprice.com/prospectus |
| Expenses [Text Block] | What were the fund costs for the last six months? Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment GNMA Fund - Z Class $0 0.00% |
| Expenses Paid, Amount | $ 0 |
| Expense Ratio, Percent | 0% |
| AssetsNet | $ 993,091,000 |
| Holdings Count | Holding | 770 |
| InvestmentCompanyPortfolioTurnover | 119.60% |
| Additional Fund Statistics Significance or Limits [Text Block] | What are some fund statistics? Fund Statistics Total Net Assets (000s) $993,091 Number of Portfolio Holdings 770 |
| Holdings [Text Block] | AAA Rated 1.1 % U.S. Government Agency Securities 102.3 Reserves - |
| Largest Holdings [Text Block] | Government National Mortgage Assn. 93.4 % Federal National Mortgage Assn. 6.6 Federal Home Loan Mortgage 2.3 Tricon Residential Trust 0.3 Sequoia Mortgage Trust 0.2 Tricon American Homes Trust 0.2 OBX Trust 0.2 Arroyo Mortgage Trust 0.1 Finance of America HECM Buyout 0.1 Morgan Stanley Residential Mortgage Loan Trust 0.1 |
| Material Fund Change [Text Block] | |
| Updated Prospectus Web Address | www.troweprice.com/paperless |
| Shareholder Report, Holdings (Details) | Nov. 30, 2024 |
| C000005523 | Government National Mortgage Assn. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 93.40% |
| C000005523 | Federal National Mortgage Assn. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.60% |
| C000005523 | Federal Home Loan Mortgage | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| C000005523 | Tricon Residential Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| C000005523 | Sequoia Mortgage Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| C000005523 | Tricon American Homes Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| C000005523 | OBX Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| C000005523 | Arroyo Mortgage Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| C000005523 | Finance of America HECM Buyout | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| C000005523 | Morgan Stanley Residential Mortgage Loan Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| C000005523 | AAA Rated | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.10% |
| C000005523 | U.S. Government Agency Securities | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 102.30% |
| C000005523 | Other Holdings Grouping | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | (3.40%) |
| C000190558 | Government National Mortgage Assn. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 93.40% |
| C000190558 | Federal National Mortgage Assn. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.60% |
| C000190558 | Federal Home Loan Mortgage | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| C000190558 | Tricon Residential Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| C000190558 | Sequoia Mortgage Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| C000190558 | Tricon American Homes Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| C000190558 | OBX Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| C000190558 | Arroyo Mortgage Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| C000190558 | Finance of America HECM Buyout | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| C000190558 | Morgan Stanley Residential Mortgage Loan Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| C000190558 | AAA Rated | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.10% |
| C000190558 | U.S. Government Agency Securities | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 102.30% |
| C000190558 | Other Holdings Grouping | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | (3.40%) |
| C000225814 | Government National Mortgage Assn. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 93.40% |
| C000225814 | Federal National Mortgage Assn. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.60% |
| C000225814 | Federal Home Loan Mortgage | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| C000225814 | Tricon Residential Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.30% |
| C000225814 | Sequoia Mortgage Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| C000225814 | Tricon American Homes Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| C000225814 | OBX Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.20% |
| C000225814 | Arroyo Mortgage Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| C000225814 | Finance of America HECM Buyout | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| C000225814 | Morgan Stanley Residential Mortgage Loan Trust | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.10% |
| C000225814 | AAA Rated | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.10% |
| C000225814 | U.S. Government Agency Securities | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 102.30% |
| C000225814 | Other Holdings Grouping | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | (3.40%) |
