S000003880 [Member] Investment Risks - Putnam VT Core Equity Fund	Dec. 31, 2025
Market risks [Member]
Prospectus [Line Items]
Risk [Text Block]	Market risk: The value of investments in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general economic, political or financial market conditions, investor sentiment and market perceptions, government actions, geopolitical events or changes, outbreaks of infectious illnesses or other widespread public health issues, and factors related to a specific issuer, asset class, geography, industry or sector. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings, may negatively impact the fund’s performance, and may exacerbate other risks to which the fund is subject.
Common stock risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Common stock risk: Common stock represents an ownership interest in a company. The value of a company’s stock may fall or fail to rise as a result of factors directly relating to that company, such as decisions made by its management or lower demand for the company’s products or services. A stock’s value may also fall because of factors affecting not just the company, but also other companies in the same industry or in a number of different industries, such as increases in production costs. Growth stocks may be more susceptible to earnings disappointments, and value stocks may fail to rebound. These risks are generally greater for small and midsize companies.
Liquidity and illiquid investments risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Liquidity and illiquid investments risk: The fund may invest up to 15% of its net assets in illiquid investments, which may be considered speculative and which may be difficult to sell. The fund may not be able to sell its illiquid investments when the Investment Manager considers it desirable to do so, or the fund may be able to sell them only at less than their value.
Short sales risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Short sales risk: The fund may engage in short sales, which are transactions in which the fund sells a security it does not own to a third party by borrowing the security in anticipation of purchasing the same security at the market price on a later date to close out the short position. If the price of the security sold short increases between the time of the short sale and the time the fund replaces the borrowed security, the fund will incur a loss that is theoretically unlimited. The fund’s investment strategy of reinvesting proceeds received from selling securities short may effectively create leverage, which can amplify the effects of market volatility on the fund’s share price and make the fund’s returns more volatile. The use of leverage may also cause the fund to liquidate portfolio positions when it would not be advantageous to do so in order to satisfy its obligations.
Large shareholder transaction risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Large shareholder transaction risk: The fund is subject to the risk that shareholders will purchase or redeem large quantities of shares of the fund. The fund may be an investment option for mutual funds that are managed by the Investment Manager and its affiliates as “funds of funds.” Additionally, other investors from time to time may make substantial investments in the fund. Such shareholders may at times be considered to control the fund. In addition, a large number of shareholders may collectively purchase or redeem fund shares in large amounts rapidly or unexpectedly. Large shareholder transactions may adversely affect the fund’s liquidity and net assets. These redemptions may also adversely affect the fund’s performance if the fund is forced to sell securities, which may also increase the fund’s brokerage costs.
Management and operational risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Management and operational risk: There is no guarantee that the investment techniques, analyses, or judgments that the Investment Manager applies in making investment decisions for the fund will produce the intended outcome or that the investments selected for the fund will perform as well as other securities that were not selected for the fund. The Investment Manager, or the fund’s other service providers, may experience disruptions or operating errors that could negatively impact the fund. The fund may not achieve its goal, and it is not intended to be a complete investment program. An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Member]
Prospectus [Line Items]
Risk [Text Block]	It is important to understand that you can lose money by investing in the fund.
Risk Not Insured [Member]
Prospectus [Line Items]
Risk [Text Block]	An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

S000003880 [Member] Investment Risks - Putnam VT Core Equity Fund

Dec. 31, 2025

Market risk: The value of investments in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general economic, political or financial market conditions, investor sentiment and market perceptions, government actions, geopolitical events or changes, outbreaks of infectious illnesses or other widespread public health issues, and factors related to a specific issuer, asset class, geography, industry or sector. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings, may negatively impact the fund’s performance, and may exacerbate other risks to which the fund is subject.

Prospectus [Line Items]

Risk [Text Block]

Common stock risk: Common stock represents an ownership interest in a company. The value of a company’s stock may fall or fail to rise as a result of factors directly relating to that company, such as decisions made by its management or lower demand for the company’s products or services. A stock’s value may also fall because of factors affecting not just the company, but also other companies in the same industry or in a number of different industries, such as increases in production costs. Growth stocks may be more susceptible to earnings disappointments, and value stocks may fail to rebound. These risks are generally greater for small and midsize companies.

Liquidity and illiquid investments risk [Member]

Prospectus [Line Items]

Risk [Text Block]

Liquidity and illiquid investments risk: The fund may invest up to 15% of its net assets in illiquid investments, which may be considered speculative and which may be difficult to sell. The fund may not be able to sell its illiquid investments when the Investment Manager considers it desirable to do so, or the fund may be able to sell them only at less than their value.

Short sales risk [Member]

Prospectus [Line Items]

Risk [Text Block]

Short sales risk: The fund may engage in short sales, which are transactions in which the fund sells a security it does not own to a third party by borrowing the security in anticipation of purchasing the same security at the market price on a later date to close out the short position. If the price of the security sold short increases between the time of the short sale and the time the fund replaces the borrowed security, the fund will incur a loss that is theoretically unlimited. The fund’s investment strategy of reinvesting proceeds received from selling securities short may effectively create leverage, which can amplify the effects of market volatility on the fund’s share price and make the fund’s returns more volatile. The use of leverage may also cause the fund to liquidate portfolio positions when it would not be advantageous to do so in order to satisfy its obligations.

Large shareholder transaction risk [Member]

Prospectus [Line Items]

Risk [Text Block]

Large shareholder transaction risk: The fund is subject to the risk that shareholders will purchase or redeem large quantities of shares of the fund. The fund may be an investment option for mutual funds that are managed by the Investment Manager and its affiliates as “funds of funds.” Additionally, other investors from time to time may make substantial investments in the fund. Such shareholders may at times be considered to control the fund. In addition, a large number of shareholders may collectively purchase or redeem fund shares in large amounts rapidly or unexpectedly. Large shareholder transactions may adversely affect the fund’s liquidity and net assets. These redemptions may also adversely affect the fund’s performance if the fund is forced to sell securities, which may also increase the fund’s brokerage costs.

Management and operational risk [Member]

Prospectus [Line Items]

Risk [Text Block]

Management and operational risk: There is no guarantee that the investment techniques, analyses, or judgments that the Investment Manager applies in making investment decisions for the fund will produce the intended outcome or that the investments selected for the fund will perform as well as other securities that were not selected for the fund. The Investment Manager, or the fund’s other service providers, may experience disruptions or operating errors that could negatively impact the fund.

The fund may not achieve its goal, and it is not intended to be a complete investment program. An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Member]

Prospectus [Line Items]

Risk [Text Block]

It is important to understand that you can lose money by investing in the fund.

Risk Not Insured [Member]

Prospectus [Line Items]

Risk [Text Block]

An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.