| Form N-CSR Cover | 12 Months Ended |
| May 31, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| 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 | May 31, 2024 |
| Shareholder Report | 12 Months Ended |
| May 31, 2024 USD ($) Holding | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| 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 | May 31, 2024 |
| C000225814 | |
| Shareholder Report [Line Items] | |
| Fund Name | GNMA Fund |
| Class Name | Z Class |
| Trading Symbol | (TRZGX) |
| Annual or Semi-Annual Statement [Text Block] | Annual Shareholder Report |
| Shareholder Report Annual or Semi-Annual | annual shareholder report |
| Additional Information [Text Block] | You can find the funds prospectus, financial information on Form N-CSR (which includes required tax information for dividends), holdings, proxy voting information, and other information at |
| Expenses [Text Block] | What were the fund costs for the last year? 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% |
| Factors Affecting Performance [Text Block] | What drove fund performance during the past 12 months? Mortgage-backed securities, including GNMAs, generated modestly positive performance for the 12-month period. The sector had one of its strongest quarters ever at the end of 2023 as the Federal Reserves more dovish tone helped calm interest rate volatility, although rising U.S. Treasury yields over the 12-month period restrained total returns. The yield generated by the funds cash holdings, which serve as collateral for our to-be-announced (TBA) positions, contributed to relative performance versus the style-specific Bloomberg U.S. GNMA Index. Relative results were also aided by an allocation to interest-only collateralized mortgage obligation positions, which benefited from higher mortgage rates that caused principal prepayments to slow, thereby sustaining interest payments. The funds use of TBAs detracted from results versus the style-specific benchmark as these instruments generally underperformed cash bonds that offered more stable cash flows. We reduced usage of TBAswhich are selected by the seller and delivered at a later dateas the period progressed in favor of specified mortgage pools. The fund seeks high current income consistent with high overall credit quality and moderate price fluctuation by investing primarily in GNMA mortgage-backed securities and investments linked to these securities. At period-end, we had a significant allocation to GNMAs with lower current coupons, which trade at discounted prices and are attractive, in our view, due to their modest prepayment risk. |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 1 Year Since Inception 2/22/2021 GNMA Fund (Z Class) 1.25 % - % Bloomberg U.S. Aggregate Bond Index (Regulatory Benchmark) 1.31 - Bloomberg U.S. GNMA Index (Strategy Benchmark) 0.88 - The preceding line graph shows the value of a hypothetical $10,000 investment in the fund over the past 10 fiscal year periods or since inception (for funds lacking 10-year records). The funds performance information included in the line graph and table above is compared with a regulatory required index that represents an overall securities market (Regulatory Benchmark). In addition, the line graph and table may also include one or more indexes that more closely aligns to the fund's investment strategy (Strategy Benchmark(s)). Due to new SEC Rules on shareholder reporting the fund adopted a new broad-based securities market index, referred to as the Regulatory Benchmark. Market index returns do not include expenses, which are deducted from fund returns. The fund's total return figures reflect the reinvestment of dividends and capital gains, if any. Neither the funds returns nor the index returns reflect the deduction of taxes that a shareholder would pay on fund distributions or redemptions of fund shares. The funds past performance is not a good predictor of the funds future performance. www.troweprice.com |
| AssetsNet | $ 998,547,000 |
| Holdings Count | Holding | 748 |
| Advisory Fees Paid, Amount | $ 1,079,000 |
| InvestmentCompanyPortfolioTurnover | 304.50% |
| Additional Fund Statistics [Text Block] | What are some fund statistics? Fund Statistics Total Net Assets (000s) $998,547 Number of Portfolio Holdings 748 |
| Holdings [Text Block] | Credit Quality Allocation* AAA Rated 0.6 % U.S. Government Agency Securities 101.1 Reserves -1.7 *Credit ratings for the securities held in the Fund are provided by Moodys, Standard & Poors, and Fitch and are converted to the Standard & Poors nomenclature. A rating of AAA represents the highest-rated securities, and a rating of D represents the lowest rated securities. If the ratings agencies differ, the highest rating is applied to the security. If a rating is not available, the security is classified as Not Rated. The rating of the underlying investment vehicle is used to determine the creditworthiness of credit default swaps and sovereign securities. The Fund is not rated by any agency. |
| Largest Holdings [Text Block] | Top Ten Holdings Government National Mortgage Assn. 96.7 % Federal National Mortgage Assn. 4.0 Federal Home Loan Mortgage 0.9 OBX Trust 0.2 Tricon American Homes Trust 0.2 Tricon Residential Trust 0.1 Arroyo Mortgage Trust 0.1 MARQ Trust 0.0 UMBS -0.6 |
| Material Fund Change [Text Block] | |
| C000005523 | |
| Shareholder Report [Line Items] | |
| Fund Name | GNMA Fund |
| Class Name | Investor Class |
| Trading Symbol | (PRGMX) |
| Annual or Semi-Annual Statement [Text Block] | Annual Shareholder Report |
| Shareholder Report Annual or Semi-Annual | annual shareholder report |
| Additional Information [Text Block] | You can find the funds prospectus, financial information on Form N-CSR (which includes required tax information for dividends), holdings, proxy voting information, and other information at |
| Expenses [Text Block] | What were the fund costs for the last year? Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment GNMA Fund - Investor Class $62 0.62% |
| Expenses Paid, Amount | $ 62 |
| Expense Ratio, Percent | 0.62% |
| Factors Affecting Performance [Text Block] | What drove fund performance during the past 12 months? Mortgage-backed securities, including GNMAs, generated modestly positive performance for the 12-month period. The sector had one of its strongest quarters ever at the end of 2023 as the Federal Reserves more dovish tone helped calm interest rate volatility, although rising U.S. Treasury yields over the 12-month period restrained total returns. The yield generated by the funds cash holdings, which serve as collateral for our to-be-announced (TBA) positions, contributed to relative performance versus the style-specific Bloomberg U.S. GNMA Index. Relative results were also aided by an allocation to interest-only collateralized mortgage obligation positions, which benefited from higher mortgage rates that caused principal prepayments to slow, thereby sustaining interest payments. The funds use of TBAs detracted from results versus the style-specific benchmark as these instruments generally underperformed cash bonds that offered more stable cash flows. We reduced usage of TBAswhich are selected by the seller and delivered at a later dateas the period progressed in favor of specified mortgage pools. The fund seeks high current income consistent with high overall credit quality and moderate price fluctuation by investing primarily in GNMA mortgage-backed securities and investments linked to these securities. At period-end, we had a significant allocation to GNMAs with lower current coupons, which trade at discounted prices and are attractive, in our view, due to their modest prepayment risk. |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 1 Year 5 Years 10 Years GNMA Fund (Investor Class) 0.62 % - % 0.42 % Bloomberg U.S. Aggregate Bond Index (Regulatory Benchmark) 1.31 - 1.26 Bloomberg U.S. GNMA Index (Strategy Benchmark) 0.88 - 0.76 The preceding line graph shows the value of a hypothetical $10,000 investment in the fund over the past 10 fiscal year periods or since inception (for funds lacking 10-year records). The funds performance information included in the line graph and table above is compared with a regulatory required index that represents an overall securities market (Regulatory Benchmark). In addition, the line graph and table may also include one or more indexes that more closely aligns to the fund's investment strategy (Strategy Benchmark(s)). Due to new SEC Rules on shareholder reporting the fund adopted a new broad-based securities market index, referred to as the Regulatory Benchmark. Market index returns do not include expenses, which are deducted from fund returns. The fund's total return figures reflect the reinvestment of dividends and capital gains, if any. Neither the funds returns nor the index returns reflect the deduction of taxes that a shareholder would pay on fund distributions or redemptions of fund shares. The funds past performance is not a good predictor of the funds future performance. www.troweprice.com |
| AssetsNet | $ 998,547,000 |
| Holdings Count | Holding | 748 |
| Advisory Fees Paid, Amount | $ 1,079,000 |
| InvestmentCompanyPortfolioTurnover | 304.50% |
| Additional Fund Statistics [Text Block] | What are some fund statistics? Fund Statistics Total Net Assets (000s) $998,547 Number of Portfolio Holdings 748 |
| Holdings [Text Block] | Credit Quality Allocation* AAA Rated 0.6 % U.S. Government Agency Securities 101.1 Reserves -1.7 *Credit ratings for the securities held in the Fund are provided by Moodys, Standard & Poors, and Fitch and are converted to the Standard & Poors nomenclature. A rating of AAA represents the highest-rated securities, and a rating of D represents the lowest rated securities. If the ratings agencies differ, the highest rating is applied to the security. If a rating is not available, the security is classified as Not Rated. The rating of the underlying investment vehicle is used to determine the creditworthiness of credit default swaps and sovereign securities. The Fund is not rated by any agency. |
| Largest Holdings [Text Block] | Top Ten Holdings Government National Mortgage Assn. 96.7 % Federal National Mortgage Assn. 4.0 Federal Home Loan Mortgage 0.9 OBX Trust 0.2 Tricon American Homes Trust 0.2 Tricon Residential Trust 0.1 Arroyo Mortgage Trust 0.1 MARQ Trust 0.0 UMBS -0.6 |
| Material Fund Change [Text Block] | |
| C000190558 | |
| Shareholder Report [Line Items] | |
| Fund Name | GNMA Fund |
| Class Name | I Class |
| Trading Symbol | (PRXAX) |
| Annual or Semi-Annual Statement [Text Block] | Annual Shareholder Report |
| Shareholder Report Annual or Semi-Annual | annual shareholder report |
| Additional Information [Text Block] | You can find the funds prospectus, financial information on Form N-CSR (which includes required tax information for dividends), holdings, proxy voting information, and other information at |
| Expenses [Text Block] | What were the fund costs for the last year? Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment GNMA Fund - I Class $41 0.41% |
| Expenses Paid, Amount | $ 41 |
| Expense Ratio, Percent | 0.41% |
| Factors Affecting Performance [Text Block] | What drove fund performance during the past 12 months? Mortgage-backed securities, including GNMAs, generated modestly positive performance for the 12-month period. The sector had one of its strongest quarters ever at the end of 2023 as the Federal Reserves more dovish tone helped calm interest rate volatility, although rising U.S. Treasury yields over the 12-month period restrained total returns. The yield generated by the funds cash holdings, which serve as collateral for our to-be-announced (TBA) positions, contributed to relative performance versus the style-specific Bloomberg U.S. GNMA Index. Relative results were also aided by an allocation to interest-only collateralized mortgage obligation positions, which benefited from higher mortgage rates that caused principal prepayments to slow, thereby sustaining interest payments. The funds use of TBAs detracted from results versus the style-specific benchmark as these instruments generally underperformed cash bonds that offered more stable cash flows. We reduced usage of TBAswhich are selected by the seller and delivered at a later dateas the period progressed in favor of specified mortgage pools. The fund seeks high current income consistent with high overall credit quality and moderate price fluctuation by investing primarily in GNMA mortgage-backed securities and investments linked to these securities. At period-end, we had a significant allocation to GNMAs with lower current coupons, which trade at discounted prices and are attractive, in our view, due to their modest prepayment risk. |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 1 Year 5 Years Since Inception 5/3/2017 GNMA Fund (I Class) 0.84 % - % 0.05 % Bloomberg U.S. Aggregate Bond Index (Regulatory Benchmark) 1.31 - 0.82 Bloomberg U.S. GNMA Index (Strategy Benchmark) 0.88 - 0.26 The preceding line graph shows the value of a hypothetical $500,000 investment in the fund over the past 10 fiscal year periods or since inception (for funds lacking 10-year records). The funds performance information included in the line graph and table above is compared with a regulatory required index that represents an overall securities market (Regulatory Benchmark). In addition, the line graph and table may also include one or more indexes that more closely aligns to the fund's investment strategy (Strategy Benchmark(s)). Due to new SEC Rules on shareholder reporting the fund adopted a new broad-based securities market index, referred to as the Regulatory Benchmark. Market index returns do not include expenses, which are deducted from fund returns. The fund's total return figures reflect the reinvestment of dividends and capital gains, if any. Neither the funds returns nor the index returns reflect the deduction of taxes that a shareholder would pay on fund distributions or redemptions of fund shares. The funds past performance is not a good predictor of the funds future performance. www.troweprice.com |
| AssetsNet | $ 998,547,000 |
| Holdings Count | Holding | 748 |
| Advisory Fees Paid, Amount | $ 1,079,000 |
| InvestmentCompanyPortfolioTurnover | 304.50% |
| Additional Fund Statistics [Text Block] | What are some fund statistics? Fund Statistics Total Net Assets (000s) $998,547 Number of Portfolio Holdings 748 |
| Holdings [Text Block] | Credit Quality Allocation* AAA Rated 0.6 % U.S. Government Agency Securities 101.1 Reserves -1.7 *Credit ratings for the securities held in the Fund are provided by Moodys, Standard & Poors, and Fitch and are converted to the Standard & Poors nomenclature. A rating of AAA represents the highest-rated securities, and a rating of D represents the lowest rated securities. If the ratings agencies differ, the highest rating is applied to the security. If a rating is not available, the security is classified as Not Rated. The rating of the underlying investment vehicle is used to determine the creditworthiness of credit default swaps and sovereign securities. The Fund is not rated by any agency. |
| Largest Holdings [Text Block] | Top Ten Holdings Government National Mortgage Assn. 96.7 % Federal National Mortgage Assn. 4.0 Federal Home Loan Mortgage 0.9 OBX Trust 0.2 Tricon American Homes Trust 0.2 Tricon Residential Trust 0.1 Arroyo Mortgage Trust 0.1 MARQ Trust 0.0 UMBS -0.6 |
| Material Fund Change [Text Block] |
| Shareholder Report, Average Annual Return (Details) | 12 Months Ended | 39 Months Ended | 60 Months Ended | 85 Months Ended | 120 Months Ended |
| May 31, 2024 | May 31, 2024 | May 31, 2024 | May 31, 2024 | May 31, 2024 | |
| Without Sales Load [Member] | C000225814 | |||||
| Average Annual Return [Line Items] | |||||
| Average Annual Return, Percent | 1.25% | (2.59%) | |||
| Without Sales Load [Member] | C000005523 | |||||
| Average Annual Return [Line Items] | |||||
| Average Annual Return, Percent | 0.62% | (0.89%) | 0.42% | ||
| Without Sales Load [Member] | C000190558 | |||||
| Average Annual Return [Line Items] | |||||
| Average Annual Return, Percent | 0.84% | (0.73%) | 0.05% | ||
| Bloomberg U.S. Aggregate Bond Index | |||||
| Average Annual Return [Line Items] | |||||
| Average Annual Return, Percent | 1.31% | (2.93%) | |||
| Bloomberg U.S. Aggregate Bond Index | |||||
| Average Annual Return [Line Items] | |||||
| Average Annual Return, Percent | 1.31% | (0.17%) | 1.26% | ||
| Bloomberg U.S. Aggregate Bond Index | |||||
| Average Annual Return [Line Items] | |||||
| Average Annual Return, Percent | 1.31% | (0.17%) | 0.82% | ||
| Bloomberg U.S. GNMA Index | |||||
| Average Annual Return [Line Items] | |||||
| Average Annual Return, Percent | 0.88% | (2.72%) | |||
| Bloomberg U.S. GNMA Index | |||||
| Average Annual Return [Line Items] | |||||
| Average Annual Return, Percent | 0.88% | (0.70%) | 0.76% | ||
| Bloomberg U.S. GNMA Index | |||||
| Average Annual Return [Line Items] | |||||
| Average Annual Return, Percent | 0.88% | (0.70%) | 0.26% |
| Shareholder Report, Holdings (Details) | May 31, 2024 |
| C000225814 | AAA Rated | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| C000225814 | U.S. Government Agency Securities | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 101.10% |
| C000005523 | AAA Rated | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| C000005523 | U.S. Government Agency Securities | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 101.10% |
| C000190558 | AAA Rated | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| C000190558 | U.S. Government Agency Securities | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 101.10% |
