| Form N-CSR Cover | 12 Months Ended |
| Dec. 31, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| Amendment Flag | false |
| Registrant Name | PUTNAM VARIABLE TRUST |
| Entity Central Index Key | 0000822671 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Dec. 31, 2024 |
| Shareholder Report | 12 Months Ended | |
| Dec. 31, 2024 USD ($) $ / shares | ||
| Shareholder Report [Line Items] | ||
| Document Type | N-CSR | |
| Amendment Flag | false | |
| Registrant Name | PUTNAM VARIABLE TRUST | |
| Entity Central Index Key | 0000822671 | |
| Entity Investment Company Type | N-1A | |
| Document Period End Date | Dec. 31, 2024 | |
| Class IA | ||
| Shareholder Report [Line Items] | ||
| Fund Name | Putnam VT Research Fund | |
| Class Name | Class IA | |
| No Trading Symbol | true | |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about Putnam VT Research Fund for the period January 1, 2024, to December 31, 2024. | |
| Shareholder Report Annual or Semi-Annual | annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents . You can also request this information by contacting us at (800) 225-1581 . | |
| Material Fund Change Notice [Text Block] | This report describes changes to the Fund that occurred during the reporting period. | |
| Additional Information Phone Number | (800) 225-1581 | |
| Additional Information Website | https://www.franklintempleton.com/regulatory-fund-documents | |
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment Class IA 1 $79 0.70% | [1] |
| Expenses Paid, Amount | $ 79 | [1] |
| Expense Ratio, Percent | 0.70% | [1] |
| Factors Affecting Performance [Text Block] | HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE? For the twelve months ended December 31, 2024, Class IA shares of Putnam VT Research Fund returned 26.61%. The Fund compares its performance to the S&P 500 Index, which returned 25.02% for the same period. PERFORMANCE HIGHLIGHTS Top contributors to performance: ↑ Overweight position in Oracle, a cloud application and platform services company ↑ Not owning Intel, a multinational technology company ↑ Overweight position in NRG Energy Top detractors from performance: ↓ Overweight position in IT company Advanced Micro Devices ↓ Out-of-benchmark position in AIA Group, a multinational financial services company ↓ Overweight position in data storage company Seagate Technology | |
| Performance Past Does Not Indicate Future [Text] | The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future. | |
| Line Graph [Table Text Block] | ||
| Average Annual Return [Table Text Block] | AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended December 31, 2024 1 Year 5 Year 10 Year Class IA 26.61 15.20 13.30 Russell 3000 Index 23.81 13.86 12.55 S&P 500 Index 25.02 14.53 13.10 | |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. | |
| Material Change Date | Jan. 01, 2024 | |
| Updated Performance Information Location [Text Block] | Important data provider notices and terms available at www.franklintempletondatasources.com. | |
| Net Assets | $ 102,789,142 | |
| Holdings Count | $ / shares | 171 | [2] |
| Advisory Fees Paid, Amount | $ 503,113 | |
| Investment Company Portfolio Turnover | 37% | |
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (as of December 31, 2024) Total Net Assets $102,789,142 Total Number of Portfolio Holdings * 171 Total Management Fee Paid $503,113 Portfolio Turnover Rate 37% | [2] |
| Holdings [Text Block] | [3] | |
| Material Fund Change [Text Block] | HOW HAS THE FUND CHANGED? On May 31, 2023, Franklin Resources, Inc. (“Franklin Templeton”) and Great-West Lifeco Inc., the parent company of Putnam U.S. Holdings I, LLC (“Putnam Holdings”), announced that they had entered into a definitive agreement for a subsidiary of Franklin Templeton to acquire Putnam Holdings in a stock and cash transaction (the “Transaction”). The Transaction was completed on January 1, 2024. As part of the Transaction, your Fund’s investment advisor, Putnam Investment Management, LLC (“Putnam Management”), a wholly-owned subsidiary of Putnam Holdings, and your Fund’s then-current sub-advisors, Putnam Investments Limited (“PIL”) and The Putnam Advisory Company, LLC (“PAC”), indirect, wholly-owned subsidiaries of Putnam Holdings, became indirect, wholly-owned subsidiaries of Franklin Templeton. In connection with the Transaction, shareholders of your Fund approved a new management contract with Putnam Management and new sub-advisory contracts with PIL and PAC. The new contracts were identical to the previous contracts, except for the effective dates, initial terms, updates to fund names as necessary to reflect previous name changes, and certain non-substantive changes. Effective July 15, 2024, Franklin Advisers, Inc. (“Franklin Advisers”) was retained as a sub-advisor by Putnam Management for the Fund pursuant to a new sub-advisory agreement between Franklin Advisers and Putnam Management. Franklin Advisers is a direct, wholly-owned subsidiary of Franklin Templeton. Effective November 1, 2024 (the “Effective Date”), PIL, a sub-advisor of the Fund prior to the Effective Date, merged with and into Franklin Templeton Investment Management Limited (“FTIML”), a wholly-owned subsidiary of Franklin Templeton (the “Merger”). As of the Effective Date, PIL investment professionals became employees of FTIML, and the sub-advisory agreement between Putnam Management and PIL with respect to the Fund was terminated. In connection with the Merger, the Fund’s Trustees approved a new sub-advisory agreement between Putnam Management and FTIML, pursuant to which FTIML became a sub-advisor of the Fund on the Effective Date. Effective July 31, 2024, the portfolio managers for the Fund are Kathryn Lakin, Jacquelyne Cavanaugh, Matthew LaPlant, Andrew O’Brien and William Rives. This is a summary of certain changes to the Fund since January 1, 2024 . For more complete information, you may review the Fund’s current prospectus and any applicable supplements and the Fund’s next prospectus, which we expect to be available by May 1, 2025, at https://www.franklintempleton.com/regulatory-fund-documents or upon request at (800) 225-1581 or funddocuments putnam.com . | |
| Updated Prospectus Phone Number | (800) 225-1581 | |
| Updated Prospectus Email Address | funddocuments@putnam.com | |
| Updated Prospectus Web Address | https://www.franklintempleton.com/regulatory-fund-documents | |
| Class IB | ||
| Shareholder Report [Line Items] | ||
| Fund Name | Putnam VT Research Fund | |
| Class Name | Class IB | |
| No Trading Symbol | true | |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about Putnam VT Research Fund for the period January 1, 2024, to December 31, 2024. | |
| Shareholder Report Annual or Semi-Annual | annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents . You can also request this information by contacting us at (800) 225-1581 . | |
| Material Fund Change Notice [Text Block] | This report describes changes to the Fund that occurred during the reporting period. | |
| Additional Information Phone Number | (800) 225-1581 | |
| Additional Information Website | https://www.franklintempleton.com/regulatory-fund-documents | |
| Expenses [Text Block] | WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment Class IB 1 $107 0.95% | [4] |
| Expenses Paid, Amount | $ 107 | [4] |
| Expense Ratio, Percent | 0.95% | [4] |
| Factors Affecting Performance [Text Block] | HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE? For the twelve months ended December 31, 2024, Class IB shares of Putnam VT Research Fund returned 26.28%. The Fund compares its performance to the S&P 500 Index, which returned 25.02% for the same period. PERFORMANCE HIGHLIGHTS Top contributors to performance: ↑ Overweight position in Oracle, a cloud application and platform services company ↑ Not owning Intel, a multinational technology company ↑ Overweight position in NRG Energy Top detractors from performance: ↓ Overweight position in IT company Advanced Micro Devices ↓ Out-of-benchmark position in AIA Group, a multinational financial services company ↓ Overweight position in data storage company Seagate Technology | |
| Performance Past Does Not Indicate Future [Text] | The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future. | |
| Line Graph [Table Text Block] | ||
| Average Annual Return [Table Text Block] | AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended December 31, 2024 1 Year 5 Year 10 Year Class IB 26.28 14.91 13.02 Russell 3000 Index 23.81 13.86 12.55 S&P 500 Index 25.02 14.53 13.10 | |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares. | |
| Material Change Date | Jan. 01, 2024 | |
| Updated Performance Information Location [Text Block] | Important data provider notices and terms available at www.franklintempletondatasources.com. | |
| Net Assets | $ 102,789,142 | |
| Holdings Count | $ / shares | 171 | [5] |
| Advisory Fees Paid, Amount | $ 503,113 | |
| Investment Company Portfolio Turnover | 37% | |
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (as of December 31, 2024) Total Net Assets $102,789,142 Total Number of Portfolio Holdings * 171 Total Management Fee Paid $503,113 Portfolio Turnover Rate 37% | [5] |
| Holdings [Text Block] | [6] | |
| Material Fund Change [Text Block] | HOW HAS THE FUND CHANGED? On May 31, 2023, Franklin Resources, Inc. (“Franklin Templeton”) and Great-West Lifeco Inc., the parent company of Putnam U.S. Holdings I, LLC (“Putnam Holdings”), announced that they had entered into a definitive agreement for a subsidiary of Franklin Templeton to acquire Putnam Holdings in a stock and cash transaction (the “Transaction”). The Transaction was completed on January 1, 2024. As part of the Transaction, your Fund’s investment advisor, Putnam Investment Management, LLC (“Putnam Management”), a wholly-owned subsidiary of Putnam Holdings, and your Fund’s then-current sub-advisors, Putnam Investments Limited (“PIL”) and The Putnam Advisory Company, LLC (“PAC”), indirect, wholly-owned subsidiaries of Putnam Holdings, became indirect, wholly-owned subsidiaries of Franklin Templeton. In connection with the Transaction, shareholders of your Fund approved a new management contract with Putnam Management and new sub-advisory contracts with PIL and PAC. The new contracts were identical to the previous contracts, except for the effective dates, initial terms, updates to fund names as necessary to reflect previous name changes, and certain non-substantive changes. Effective July 15, 2024, Franklin Advisers, Inc. (“Franklin Advisers”) was retained as a sub-advisor by Putnam Management for the Fund pursuant to a new sub-advisory agreement between Franklin Advisers and Putnam Management. Franklin Advisers is a direct, wholly-owned subsidiary of Franklin Templeton. Effective November 1, 2024 (the “Effective Date”), PIL, a sub-advisor of the Fund prior to the Effective Date, merged with and into Franklin Templeton Investment Management Limited (“FTIML”), a wholly-owned subsidiary of Franklin Templeton (the “Merger”). As of the Effective Date, PIL investment professionals became employees of FTIML, and the sub-advisory agreement between Putnam Management and PIL with respect to the Fund was terminated. In connection with the Merger, the Fund’s Trustees approved a new sub-advisory agreement between Putnam Management and FTIML, pursuant to which FTIML became a sub-advisor of the Fund on the Effective Date. Effective July 31, 2024, the portfolio managers for the Fund are Kathryn Lakin, Jacquelyne Cavanaugh, Matthew LaPlant, Andrew O’Brien and William Rives. This is a summary of certain changes to the Fund since January 1, 2024 . For more complete information, you may review the Fund’s current prospectus and any applicable supplements and the Fund’s next prospectus, which we expect to be available by May 1, 2025, at https://www.franklintempleton.com/regulatory-fund-documents or upon request at (800) 225-1581 or funddocuments putnam.com . | |
| Updated Prospectus Phone Number | (800) 225-1581 | |
| Updated Prospectus Email Address | funddocuments@putnam.com | |
| Updated Prospectus Web Address | https://www.franklintempleton.com/regulatory-fund-documents | |
| [1] 1 Does not reflect expenses incurred from investing through variable annuity or variable life insurance products. * Includes derivatives, if applicable. Cash and Equivalents, if any, represent the market value weights of cash, derivatives, short-term securities, and other unclassified assets in the portfolio. Holdings and allocations may vary over time. 1 Does not reflect expenses incurred from investing through variable annuity or variable life insurance products. * Includes derivatives, if applicable. Cash and Equivalents, if any, represent the market value weights of cash, derivatives, short-term securities, and other unclassified assets in the portfolio. Holdings and allocations may vary over time. | ||
| Shareholder Report, Line Graph (Details) - USD ($) | 12 Months Ended | ||||||||||
| Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | |
| Class IA | |||||||||||
| Account Value [Line Items] | |||||||||||
| Line Graph and Table Measure Name | Class IA | ||||||||||
| Account Value | $ 34,867 | $ 27,539 | $ 21,322 | $ 25,709 | $ 20,659 | $ 17,183 | $ 12,862 | $ 13,470 | $ 10,890 | $ 9,871 | $ 10,000 |
| Class IB | |||||||||||
| Account Value [Line Items] | |||||||||||
| Line Graph and Table Measure Name | Class IB | ||||||||||
| Account Value | $ 34,005 | 26,929 | 20,898 | 25,264 | 20,352 | 16,972 | 12,738 | 13,368 | 10,838 | 9,850 | 10,000 |
| Russell 3000 Index [Member] | |||||||||||
| Account Value [Line Items] | |||||||||||
| Line Graph and Table Measure Name | Russell 3000 Index | ||||||||||
| Account Value | $ 32,604 | 26,334 | 20,907 | 25,877 | 20,593 | 17,035 | 13,002 | 13,721 | 11,327 | 10,048 | 10,000 |
| Russell 3000 Index [Member] | |||||||||||
| Account Value [Line Items] | |||||||||||
| Line Graph and Table Measure Name | Russell 3000 Index | ||||||||||
| Account Value | $ 32,604 | 26,334 | 20,907 | 25,877 | 20,593 | 17,035 | 13,002 | 13,721 | 11,327 | 10,048 | 10,000 |
| S&P 500 Index [Member] | |||||||||||
| Account Value [Line Items] | |||||||||||
| Line Graph and Table Measure Name | S&P 500 Index | ||||||||||
| Account Value | $ 34,254 | 27,399 | 21,696 | 26,494 | 20,585 | 17,386 | 13,223 | 13,829 | 11,351 | 10,138 | 10,000 |
| S&P 500 Index [Member] | |||||||||||
| Account Value [Line Items] | |||||||||||
| Line Graph and Table Measure Name | S&P 500 Index | ||||||||||
| Account Value | $ 34,254 | $ 27,399 | $ 21,696 | $ 26,494 | $ 20,585 | $ 17,386 | $ 13,223 | $ 13,829 | $ 11,351 | $ 10,138 | $ 10,000 |
| Shareholder Report, Average Annual Return (Details) | 12 Months Ended | 60 Months Ended | 120 Months Ended |
| Dec. 31, 2024 | Dec. 31, 2024 | Dec. 31, 2024 | |
| Class IA | |||
| Average Annual Return [Line Items] | |||
| Line Graph and Table Measure Name | Class IA | ||
| Average Annual Return, Percent | 26.61% | 15.20% | 13.30% |
| Class IB | |||
| Average Annual Return [Line Items] | |||
| Line Graph and Table Measure Name | Class IB | ||
| Average Annual Return, Percent | 26.28% | 14.91% | 13.02% |
| Russell 3000 Index [Member] | |||
| Average Annual Return [Line Items] | |||
| Line Graph and Table Measure Name | Russell 3000 Index | ||
| Average Annual Return, Percent | 23.81% | 13.86% | 12.55% |
| Russell 3000 Index [Member] | |||
| Average Annual Return [Line Items] | |||
| Line Graph and Table Measure Name | Russell 3000 Index | ||
| Average Annual Return, Percent | 23.81% | 13.86% | 12.55% |
| S&P 500 Index [Member] | |||
| Average Annual Return [Line Items] | |||
| Line Graph and Table Measure Name | S&P 500 Index | ||
| Average Annual Return, Percent | 25.02% | 14.53% | 13.10% |
| S&P 500 Index [Member] | |||
| Average Annual Return [Line Items] | |||
| Line Graph and Table Measure Name | S&P 500 Index | ||
| Average Annual Return, Percent | 25.02% | 14.53% | 13.10% |
| Label | Element | Value |
| Class IA | Information Technology [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 30.10% |
| Class IA | Financials [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 12.60% |
| Class IA | Consumer Discretionary [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 11.80% |
| Class IA | Health Care [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 10.30% |
| Class IA | Communication Services [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 9% |
| Class IA | Industrials [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 6.70% |
| Class IA | Consumer Staples [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 6.10% |
| Class IA | Energy [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 3.30% |
| Class IA | Materials [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 3.20% |
| Class IA | Utilities [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 2.60% |
| Class IA | Real Estate [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 1.50% |
| Class IA | Cash and Equivalents [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 2.80% |
| Label | Element | Value |
| Class IB | Information Technology [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 30.10% |
| Class IB | Financials [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 12.60% |
| Class IB | Consumer Discretionary [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 11.80% |
| Class IB | Health Care [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 10.30% |
| Class IB | Communication Services [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 9% |
| Class IB | Industrials [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 6.70% |
| Class IB | Consumer Staples [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 6.10% |
| Class IB | Energy [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 3.30% |
| Class IB | Materials [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 3.20% |
| Class IB | Utilities [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 2.60% |
| Class IB | Real Estate [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 1.50% |
| Class IB | Cash and Equivalents [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 2.80% |
