| 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 Government Money Market Fund | |
| Class Name | Class IA | |
| No Trading Symbol Flag | true | |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about Putnam VT Government Money Market 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 $45 0.44% | [1] |
| Expenses Paid, Amount | $ 45 | [1] |
| Expense Ratio, Percent | 0.44% | [1] |
| Factors Affecting Performance [Text Block] | HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE? As of December 31, 2024, the seven-day current yield for Class IA shares of the Putnam VT Government Money Market Fund was 4.18% and the seven-day effective yield was 4.18%. The seven-day current yield represents net interest income generated by the Fund’s investments for the past seven days and assumes income is generated each week over a 365-day period. The seven-day effective yield assumes reinvestment of the coupon (interest payments) and will typically be slightly higher than the current yield because of the compounding effect on investment returns. The Fund has maintained a shorter weighted average maturity (WAM) posture due to our view that the U.S. Federal Reserve (Fed) rate cutting cycle will be slower and shallower relative to market expectations. As a result, the Fund’s principal exposure is to overnight repurchase agreements that are collateralized by U.S. Treasuries and/or government agency mortgage-backed securities. Additionally, the Fund maintained term exposure in the 1 to 7-month maturity range with investments in U.S. Treasuries where we saw opportunities to lock in higher yields. The Fund eliminated its exposure to Federal Home Loan Bank and Federal Farm Credit Bank securities as spreads are now less attractive, in our view. | |
| 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. | |
| Material Change Date | Jan. 01, 2024 | |
| Net Assets | $ 85,805,647 | |
| Holdings Count | $ / shares | 7 | [2] |
| Advisory Fees Paid, Amount | $ 214,499 | |
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (as of December 31, 2024) Total Net Assets $85,805,647 Total Number of Portfolio Holdings * 7 Total Management Fee Paid $214,499 | [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 then-current investment advisor, Putnam Investment Management, LLC (“Putnam Management”), a wholly-owned subsidiary of Putnam Holdings, and your Fund’s then-current sub-advisor, Putnam Investments Limited (“PIL”), an indirect, wholly-owned subsidiary 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 a new sub-advisory contract with PIL. 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, Putnam Management transferred its management contract for your Fund to Franklin Advisers, Inc. (“Franklin Advisers”), and Franklin Advisers replaced Putnam Management as the investment advisor to your Fund. In connection with the transfer, your Fund’s portfolio managers, along with supporting research analysts and certain other investment staff of Putnam Management, also became employees of Franklin Advisers. Putnam Management also transferred to Franklin Advisers its sub-management agreement with PIL in respect of your Fund. Franklin Advisers is a direct, wholly-owned subsidiary of Franklin Templeton. In addition, effective July 15, 2024, Franklin Advisers retained Putnam Management as a sub-advisor to your Fund pursuant to a new sub-advisory agreement. 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 Franklin Advisers 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 Franklin Advisers and FTIML, pursuant to which FTIML became a sub-advisor of the Fund on the Effective Date. 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 Government Money Market Fund | |
| Class Name | Class IB | |
| No Trading Symbol Flag | true | |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about Putnam VT Government Money Market 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 $71 0.69% | [4] |
| Expenses Paid, Amount | $ 71 | [4] |
| Expense Ratio, Percent | 0.69% | [4] |
| Factors Affecting Performance [Text Block] | HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE? As of December 31, 2024, the seven-day current yield for Class IB shares of the Putnam VT Government Money Market Fund was 3.93% and the seven-day effective yield was 3.93%. The seven-day current yield represents net interest income generated by the Fund’s investments for the past seven days and assumes income is generated each week over a 365-day period. The seven-day effective yield assumes reinvestment of the coupon (interest payments) and will typically be slightly higher than the current yield because of the compounding effect on investment returns. The Fund has maintained a shorter weighted average maturity (WAM) posture due to our view that the U.S. Federal Reserve (Fed) rate cutting cycle will be slower and shallower relative to market expectations. As a result, the Fund’s principal exposure is to overnight repurchase agreements that are collateralized by U.S. Treasuries and/or government agency mortgage-backed securities. Additionally, the Fund maintained term exposure in the 1 to 7-month maturity range with investments in U.S. Treasuries where we saw opportunities to lock in higher yields. The Fund eliminated its exposure to Federal Home Loan Bank and Federal Farm Credit Bank securities as spreads are now less attractive, in our view. | |
| 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. | |
| Material Change Date | Jan. 01, 2024 | |
| Net Assets | $ 85,805,647 | |
| Holdings Count | $ / shares | 7 | [5] |
| Advisory Fees Paid, Amount | $ 214,499 | |
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (as of December 31, 2024) Total Net Assets $85,805,647 Total Number of Portfolio Holdings * 7 Total Management Fee Paid $214,499 | [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 then-current investment advisor, Putnam Investment Management, LLC (“Putnam Management”), a wholly-owned subsidiary of Putnam Holdings, and your Fund’s then-current sub-advisor, Putnam Investments Limited (“PIL”), an indirect, wholly-owned subsidiary 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 a new sub-advisory contract with PIL. 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, Putnam Management transferred its management contract for your Fund to Franklin Advisers, Inc. (“Franklin Advisers”), and Franklin Advisers replaced Putnam Management as the investment advisor to your Fund. In connection with the transfer, your Fund’s portfolio managers, along with supporting research analysts and certain other investment staff of Putnam Management, also became employees of Franklin Advisers. Putnam Management also transferred to Franklin Advisers its sub-management agreement with PIL in respect of your Fund. Franklin Advisers is a direct, wholly-owned subsidiary of Franklin Templeton. In addition, effective July 15, 2024, Franklin Advisers retained Putnam Management as a sub-advisor to your Fund pursuant to a new sub-advisory agreement. 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 Franklin Advisers 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 Franklin Advisers and FTIML, pursuant to which FTIML became a sub-advisor of the Fund on the Effective Date. 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 and other unclassified assets in the portfolio and may show a negative market value percentage as a result of the timing of trade-date and settlement-date transactions. 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 and other unclassified assets in the portfolio and may show a negative market value percentage as a result of the timing of trade-date and settlement-date transactions. Holdings and allocations may vary over time. | ||
| Label | Element | Value |
| Class IA | Repurchase Agreements [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 97.50% |
| Class IA | U.S. Treasury Debt [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 3.20% |
| Class IA | Cash and Equivalents [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | (0.70%) |
| Label | Element | Value |
| Class IB | Repurchase Agreements [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 97.50% |
| Class IB | U.S. Treasury Debt [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | 3.20% |
| Class IB | Cash and Equivalents [Member] | ||
| Holdings [Line Items] | oef_HoldingsLineItems | |
| Percent of Net Asset Value | oef_PctOfNav | (0.70%) |
