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Label Element Value
Risk Return Abstract rr_RiskReturnAbstract  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Dec. 31, 2017
Registrant Name dei_EntityRegistrantName PUTNAM VARIABLE TRUST
Central Index Key dei_EntityCentralIndexKey 0000822671
Amendment Flag dei_AmendmentFlag false
Trading Symbol dei_TradingSymbol PVT
Document Creation Date dei_DocumentCreationDate Apr. 26, 2018
Document Effective Date dei_DocumentEffectiveDate Apr. 30, 2018
Prospectus Date rr_ProspectusDate May 30, 2018
Putnam VT Capital Opportunities Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Capital Opportunities Fund seeks long-term growth of capital.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 4/30/19
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 157%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 157.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Only the first year of each period in the example takes into account the expense reimbursement described above. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in common stocks (growth or value stocks or both) of small and midsize U.S. companies that we believe have favorable investment potential. For example, we may purchase stocks of companies with stock prices that reflect a value lower than that which we place on the company. We may also consider other factors we believe will cause the stock price to rise. We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. 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.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   0.66%

Best calendar quarter
Q2 2009   24.01%

Worst calendar quarter
Q4 2008 −24.85%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 0.66%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 24.01%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (24.85%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Putnam VT Capital Opportunities Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.62%
Other expenses rr_OtherExpensesOverAssets 0.39%
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.07%
Total annual fund operating expenses rr_ExpensesOverAssets 1.08%
Expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.11%) [1]
Total annual fund operating expenses after expense reimbursement rr_NetExpensesOverAssets 0.97%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 99
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 333
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 585
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,307
Annual Return 2008 rr_AnnualReturn2008 (35.01%)
Annual Return 2009 rr_AnnualReturn2009 45.98%
Annual Return 2010 rr_AnnualReturn2010 29.83%
Annual Return 2011 rr_AnnualReturn2011 (5.88%)
Annual Return 2012 rr_AnnualReturn2012 14.69%
Annual Return 2013 rr_AnnualReturn2013 34.33%
Annual Return 2014 rr_AnnualReturn2014 7.36%
Annual Return 2015 rr_AnnualReturn2015 (7.37%)
Annual Return 2016 rr_AnnualReturn2016 15.77%
Annual Return 2017 rr_AnnualReturn2017 8.26%
1 Year rr_AverageAnnualReturnYear01 8.26%
5 Years rr_AverageAnnualReturnYear05 10.86%
10 Years rr_AverageAnnualReturnYear10 8.33%
Putnam VT Capital Opportunities Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.62%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.39%
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.07%
Total annual fund operating expenses rr_ExpensesOverAssets 1.33%
Expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.11%) [1]
Total annual fund operating expenses after expense reimbursement rr_NetExpensesOverAssets 1.22%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 124
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 411
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 718
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,592
1 Year rr_AverageAnnualReturnYear01 7.93%
5 Years rr_AverageAnnualReturnYear05 10.58%
10 Years rr_AverageAnnualReturnYear10 8.06%
Putnam VT Capital Opportunities Fund | Russelll 2500 Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 16.81% [2]
5 Years rr_AverageAnnualReturnYear05 14.33% [2]
10 Years rr_AverageAnnualReturnYear10 9.22% [2]
Putnam VT Diversified Income Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Diversified Income Fund seeks as high a level of current income as Putnam Investment Management, LLC believes is consistent with preservation of capital.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 1,100%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 1100.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in bonds that are securitized debt instruments (such as mortgage-backed investments) and other obligations of companies and governments worldwide, are either investment-grade or below-investment-grade in quality (sometimes referred to as “junk bonds”) and have intermediate- to long-term maturities (three years or longer). We may consider, among other factors, credit, interest rate and prepayment risks, as well as general market conditions, when deciding whether to buy or sell investments. We typically use to a significant extent derivatives, such as futures, options, certain foreign currency transactions and swap contracts, for both hedging and non-hedging purposes.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of bonds in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions (including perceptions about the risk of default and expectations about monetary policy or interest rates), changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. The risks associated with bond investments include interest rate risk, which means the value of the fund’s investments is likely to fall if interest rates rise. Bond investments are also subject to credit risk, which is the risk that the issuer of a bond may default on payment of interest or principal. Interest rate risk is generally greater for longer-term bonds, and credit risk is generally greater for below-investment-grade bonds (a significant part of the fund’s investments). Mortgage-backed investments, unlike traditional debt investments, are also subject to prepayment risk, which means that they may increase in value less than other bonds when interest rates decline and decline in value more than other bonds when interest rates rise. We may have to invest the proceeds from prepaid investments, including mortgage-backed investments, in other investments with less attractive terms and yields. The value of international investments traded in foreign currencies may be adversely impacted by fluctuations in exchange rates. International investments, particularly investments in emerging markets, may carry risks associated with potentially less stable economies or governments (such as the risk of seizure by a foreign government, the imposition of currency or other restrictions, or high levels of inflation or deflation), and may be or become illiquid.

Our use of derivatives may increase the risks of investing in the fund by increasing investment exposure (which may be considered leverage) or, in the case of many over-the-counter instruments, because of the potential inability to terminate or sell derivatives positions and the potential failure of the other party to the instrument to meet its obligations.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   2.16%

Best calendar quarter
Q2 2009   18.40%

Worst calendar quarter
Q4 2008 −21.54%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 2.16%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.40%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (21.54%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Performance Table Market Index Changed rr_PerformanceTableMarketIndexChanged As of January 30, 2018, the ICE BofAML U.S. Treasury Bill Index replaced the Bloomberg Barclays U.S. Aggregate Bond Index as the benchmark for this fund because, in Putnam Investment Management, LLC’s opinion, this index more accurately reflects the fund’s multi-sector investment approach.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock As of January 30, 2018, the ICE BofAML U.S. Treasury Bill Index replaced the Bloomberg Barclays U.S. Aggregate Bond Index as the benchmark for this fund because, in Putnam Investment Management, LLC’s opinion, this index more accurately reflects the fund’s multi-sector investment approach.
Putnam VT Diversified Income Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.54%
Other expenses rr_OtherExpensesOverAssets 0.24%
Total annual fund operating expenses rr_ExpensesOverAssets 0.78%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 80
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 249
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 433
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 966
Annual Return 2008 rr_AnnualReturn2008 (31.07%)
Annual Return 2009 rr_AnnualReturn2009 54.83%
Annual Return 2010 rr_AnnualReturn2010 13.02%
Annual Return 2011 rr_AnnualReturn2011 (3.17%)
Annual Return 2012 rr_AnnualReturn2012 11.97%
Annual Return 2013 rr_AnnualReturn2013 8.08%
Annual Return 2014 rr_AnnualReturn2014 0.68%
Annual Return 2015 rr_AnnualReturn2015 (2.32%)
Annual Return 2016 rr_AnnualReturn2016 5.76%
Annual Return 2017 rr_AnnualReturn2017 7.42%
1 Year rr_AverageAnnualReturnYear01 7.42%
5 Years rr_AverageAnnualReturnYear05 3.85%
10 Years rr_AverageAnnualReturnYear10 4.68%
Putnam VT Diversified Income Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.54%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.24%
Total annual fund operating expenses rr_ExpensesOverAssets 1.03%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 105
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 328
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 569
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,259
1 Year rr_AverageAnnualReturnYear01 7.12%
5 Years rr_AverageAnnualReturnYear05 3.59%
10 Years rr_AverageAnnualReturnYear10 4.55%
Putnam VT Diversified Income Fund | ICE BofAML U.S. Treasury Bill Index  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 0.81%
5 Years rr_AverageAnnualReturnYear05 0.28%
10 Years rr_AverageAnnualReturnYear10 0.46%
Putnam VT Diversified Income Fund | Bloomberg Barclays U.S. Aggregate Bond Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 3.54%
5 Years rr_AverageAnnualReturnYear05 2.10%
10 Years rr_AverageAnnualReturnYear10 4.01%
Putnam VT Equity Income Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Equity Income Fund seeks capital growth and current income.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 12%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 12.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in common stocks of midsize and large U.S. companies, with a focus on value stocks that offer the potential for capital growth, current income, or both. Under normal circumstances, we invest at least 80% of the fund’s net assets in common stocks and other equity investments that offer the potential for current income. This policy may be changed only after 60 days’ notice to shareholders. Value stocks are issued by companies that we believe are currently undervalued by the market. If we are correct and other investors ultimately recognize the value of the company, the price of its stock may rise. We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer, industry or sector. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. Value stocks may fail to rebound, and the market may not favor value-style investing. Income provided by the fund may be reduced by changes in the dividend policies of, and the capital resources available at, the companies in which the fund invests.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18  −2.03%

Best calendar quarter
Q2 2009   18.31%

Worst calendar quarter
Q4 2008 −18.93%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (2.03%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.31%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (18.93%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Putnam VT Equity Income Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.47%
Other expenses rr_OtherExpensesOverAssets 0.10% [3]
Total annual fund operating expenses rr_ExpensesOverAssets 0.57%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 58
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 183
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 318
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 714
Annual Return 2008 rr_AnnualReturn2008 (31.02%)
Annual Return 2009 rr_AnnualReturn2009 27.81%
Annual Return 2010 rr_AnnualReturn2010 12.92%
Annual Return 2011 rr_AnnualReturn2011 2.07%
Annual Return 2012 rr_AnnualReturn2012 19.62%
Annual Return 2013 rr_AnnualReturn2013 32.72%
Annual Return 2014 rr_AnnualReturn2014 12.97%
Annual Return 2015 rr_AnnualReturn2015 (2.79%)
Annual Return 2016 rr_AnnualReturn2016 13.96%
Annual Return 2017 rr_AnnualReturn2017 19.06%
1 Year rr_AverageAnnualReturnYear01 19.06%
5 Years rr_AverageAnnualReturnYear05 14.61%
10 Years rr_AverageAnnualReturnYear10 9.17%
Putnam VT Equity Income Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.47%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.10% [3]
Total annual fund operating expenses rr_ExpensesOverAssets 0.82%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 84
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 262
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 455
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,014
1 Year rr_AverageAnnualReturnYear01 18.77%
5 Years rr_AverageAnnualReturnYear05 14.32%
10 Years rr_AverageAnnualReturnYear10 8.90%
Putnam VT Equity Income Fund | Russell 1000 Value Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 13.66% [2]
5 Years rr_AverageAnnualReturnYear05 14.04% [2]
10 Years rr_AverageAnnualReturnYear10 7.10% [2]
Putnam VT George Putnam Balanced Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT George Putnam Balanced Fund seeks to provide a balanced investment composed of a well-diversified portfolio of stocks and bonds which produce both capital growth and current income.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 191%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 191.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in a combination of bonds and common stocks (growth or value stocks or both) of large U.S. companies, with a greater focus on common stocks. For example, we may purchase stocks of companies with stock prices that reflect a value lower than that which we place on the company. We may also consider other factors that we believe will cause the stock price to rise. We buy bonds of governments and private companies that are mostly investment-grade in quality with intermediate- to long-term maturities (three years or longer). We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell equity investments, and, among other factors, credit, interest rate and prepayment risks, as well as general market conditions, when deciding whether to buy or sell fixed-income investments. We may also use derivatives, such as futures, options, warrants and swap contracts, for both hedging and non-hedging purposes.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks and bonds in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions (including, in the case of bonds, perceptions about the risk of default and expectations about monetary policy or interest rates), changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. Growth stocks may be more susceptible to earnings disappointments, and value stocks may fail to rebound.

Bond investments are subject to interest rate risk, which means the value of the fund’s bond investments is likely to fall if interest rates rise. Bond investments also are subject to credit risk, which is the risk that the issuer of the bond may default on payment of interest or principal. Interest rate risk is generally greater for longer-term bonds, and credit risk is generally greater for below-investment-grade bonds (sometimes referred to as “junk bonds”), which may be considered speculative. Our use of derivatives may increase the risks of investing in the fund by increasing investment exposure (which may be considered leverage) or, in the case of many over-the-counter instruments, because of the potential inability to terminate or sell derivatives positions and the potential failure of the other party to the instrument to meet its obligations.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18  −0.86%

Best calendar quarter
Q2 2009   13.04%

Worst calendar quarter
Q4 2008 −27.53%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (0.86%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 13.04%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (27.53%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock The fund’s performance is compared to the Bloomberg Barclays U.S. Aggregate Bond Index, an unmanaged index of U.S. investment-grade fixed income securities. The fund’s performance is also compared to the S&P 500 Index, an unmanaged index of large U.S. company stocks. In addition, the fund’s performance is compared to the George Putnam Blended Index, an unmanaged index administered by Putnam Management, 60% of which is the S&P 500 Index and 40% of which is the Bloomberg Barclays U.S. Aggregate Bond Index.
Putnam VT George Putnam Balanced Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.52%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 0.73%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 75
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 233
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 406
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 906
Annual Return 2008 rr_AnnualReturn2008 (40.57%)
Annual Return 2009 rr_AnnualReturn2009 26.10%
Annual Return 2010 rr_AnnualReturn2010 11.20%
Annual Return 2011 rr_AnnualReturn2011 2.88%
Annual Return 2012 rr_AnnualReturn2012 12.77%
Annual Return 2013 rr_AnnualReturn2013 18.46%
Annual Return 2014 rr_AnnualReturn2014 10.93%
Annual Return 2015 rr_AnnualReturn2015 (0.96%)
Annual Return 2016 rr_AnnualReturn2016 8.40%
Annual Return 2017 rr_AnnualReturn2017 15.29%
1 Year rr_AverageAnnualReturnYear01 15.29%
5 Years rr_AverageAnnualReturnYear05 10.22%
10 Years rr_AverageAnnualReturnYear10 4.63%
Putnam VT George Putnam Balanced Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.52%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 0.98%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 100
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 312
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 542
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,201
1 Year rr_AverageAnnualReturnYear01 15.08%
5 Years rr_AverageAnnualReturnYear05 9.94%
10 Years rr_AverageAnnualReturnYear10 4.37%
Putnam VT George Putnam Balanced Fund | S&P 500 Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 21.83%
5 Years rr_AverageAnnualReturnYear05 15.79%
10 Years rr_AverageAnnualReturnYear10 8.50%
Putnam VT George Putnam Balanced Fund | Bloomberg Barclays U.S. Aggregate Bond Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 3.54%
5 Years rr_AverageAnnualReturnYear05 2.10%
10 Years rr_AverageAnnualReturnYear10 4.01%
Putnam VT George Putnam Balanced Fund | George Putnam Blended Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 14.25%
5 Years rr_AverageAnnualReturnYear05 10.33%
10 Years rr_AverageAnnualReturnYear10 7.29%
Putnam VT Global Asset Allocation Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Global Asset Allocation Fund seeks long-term return consistent with preservation of capital.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 208%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 208.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest a majority of the fund’s assets in a diversified portfolio of equity securities (growth or value stocks or both) of both U.S. and foreign companies of any size. We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell equity investments. We also invest in a diversified portfolio of fixed-income investments, including both U.S. and foreign government obligations, corporate obligations and securitized debt instruments (such as mortgage-backed investments). We may consider, among other factors, credit, interest rate and prepayment risks, as well as general market conditions, when deciding whether to buy or sell fixed income investments. We may also select other investments that do not fall within these asset classes. We may also use to a significant extent derivatives, such as futures, options, certain foreign currency transactions, warrants and swap contracts, for both hedging and non-hedging purposes.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

Our allocation of assets among asset classes may hurt performance. The value of stocks and bonds in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions (including, in the case of bonds, perceptions about the risk of default and expectations about monetary policy or interest rates), changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. 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.

Bond investments are subject to interest rate risk, which means the value of the fund’s bond investments is likely to fall if interest rates rise. Bond investments also are subject to credit risk, which is the risk that the issuer of the bond may default on payment of interest or principal. Interest rate risk is generally greater for longer-term bonds, and credit risk is generally greater for below-investment-grade bonds (sometimes referred to as “junk bonds”), which may be considered speculative. Mortgage-backed investments, unlike traditional debt investments, are also subject to prepayment risk, which means that they may increase in value less than other bonds when interest rates decline and decline in value more than other bonds when interest rates rise. We may have to invest the proceeds from prepaid investments, including mortgage-and asset-backed investments, in other investments with less attractive terms and yields.

The value of international investments traded in foreign currencies may be adversely impacted by fluctuations in exchange rates. International investments, particularly investments in emerging markets, may carry risks associated with potentially less stable economies or governments (such as the risk of seizure by a foreign government, the imposition of currency or other restrictions, or high levels of inflation), and may be or become illiquid. Our use of derivatives may increase the risks of investing in the fund by increasing investment exposure (which may be considered leverage) or, in the case of many over-the-counter instruments, because of the potential inability to terminate or sell derivatives positions and the potential failure of the other party to the instrument to meet its obligations.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18  −1.94%

Best calendar quarter
Q2 2009   16.12%

Worst calendar quarter
Q4 2008 −19.54%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (1.94%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 16.12%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (19.54%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock Putnam Balanced Blended Benchmark is an unmanaged index administered by Putnam Investment Management, LLC, 50% of which is the Russell 3000 Index, 35% of which is the Bloomberg Barclays U.S. Aggregate Bond Index, 10% of which is the MSCI EAFE Index (ND) and 5% of which is the JPMorgan Developed High Yield Index.
Putnam VT Global Asset Allocation Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.59%
Other expenses rr_OtherExpensesOverAssets 0.27%
Total annual fund operating expenses rr_ExpensesOverAssets 0.86%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 88
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 274
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 477
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,061
Annual Return 2008 rr_AnnualReturn2008 (33.16%)
Annual Return 2009 rr_AnnualReturn2009 35.36%
Annual Return 2010 rr_AnnualReturn2010 14.94%
Annual Return 2011 rr_AnnualReturn2011 (0.18%)
Annual Return 2012 rr_AnnualReturn2012 14.58%
Annual Return 2013 rr_AnnualReturn2013 19.78%
Annual Return 2014 rr_AnnualReturn2014 9.66%
Annual Return 2015 rr_AnnualReturn2015 0.42%
Annual Return 2016 rr_AnnualReturn2016 6.98%
Annual Return 2017 rr_AnnualReturn2017 15.67%
1 Year rr_AverageAnnualReturnYear01 15.67%
5 Years rr_AverageAnnualReturnYear05 10.29%
10 Years rr_AverageAnnualReturnYear10 6.86%
Putnam VT Global Asset Allocation Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.59%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.27%
Total annual fund operating expenses rr_ExpensesOverAssets 1.11%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 113
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 353
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 612
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,352
1 Year rr_AverageAnnualReturnYear01 15.34%
5 Years rr_AverageAnnualReturnYear05 10.02%
10 Years rr_AverageAnnualReturnYear10 6.60%
Putnam VT Global Asset Allocation Fund | Russell 3000 Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 21.13% [2]
5 Years rr_AverageAnnualReturnYear05 15.58% [2]
10 Years rr_AverageAnnualReturnYear10 8.60% [2]
Putnam VT Global Asset Allocation Fund | Putnam Balanced Blended Benchmark (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 14.41%
5 Years rr_AverageAnnualReturnYear05 9.61%
10 Years rr_AverageAnnualReturnYear10 6.63%
Putnam VT Global Equity Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Global Equity Fund seeks capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 75%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 75.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in common stocks (growth or value stocks or both) of large and midsize companies worldwide that we believe have favorable investment potential. For example, we may purchase stocks of companies with stock prices that reflect a value lower than that which we place on the company. Under normal circumstances, we invest at least 80% of the fund’s net assets in equity investments. This policy may be changed only after 60 days’ notice to shareholders. We may also consider other factors that we believe will cause the stock price to rise. We invest mainly in developed countries, but may invest in emerging markets. We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments. We may also use derivatives, such as futures, options, certain foreign currency transactions, warrants and swap contracts, for both hedging and non-hedging purposes.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. 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. The value of international investments traded in foreign currencies may be adversely impacted by fluctuations in exchange rates. International investments, particularly investments in emerging markets, may carry risks associated with potentially less stable economies or governments (such as the risk of seizure by a foreign government, the imposition of currency or other restrictions, or high levels of inflation or deflation), and may be or become illiquid. Our use of derivatives may increase the risks of investing in the fund by increasing investment exposure (which may be considered leverage) or, in the case of many over-the-counter instruments, because of the potential inability to terminate or sell derivatives positions and the potential failure of the other party to the instrument to meet its obligations.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18  −0.05%

Best calendar quarter
Q2 2009   22.27%

Worst calendar quarter
Q4 2008 −23.60%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (0.05%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 22.27%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (23.60%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Putnam VT Global Equity Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.69%
Other expenses rr_OtherExpensesOverAssets 0.18%
Total annual fund operating expenses rr_ExpensesOverAssets 0.87%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 89
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 278
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 482
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,073
Annual Return 2008 rr_AnnualReturn2008 (45.24%)
Annual Return 2009 rr_AnnualReturn2009 30.16%
Annual Return 2010 rr_AnnualReturn2010 10.22%
Annual Return 2011 rr_AnnualReturn2011 (4.78%)
Annual Return 2012 rr_AnnualReturn2012 20.55%
Annual Return 2013 rr_AnnualReturn2013 32.27%
Annual Return 2014 rr_AnnualReturn2014 1.77%
Annual Return 2015 rr_AnnualReturn2015 (1.49%)
Annual Return 2016 rr_AnnualReturn2016 1.37%
Annual Return 2017 rr_AnnualReturn2017 28.71%
1 Year rr_AverageAnnualReturnYear01 28.71%
5 Years rr_AverageAnnualReturnYear05 11.59%
10 Years rr_AverageAnnualReturnYear10 4.55%
Putnam VT Global Equity Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.69%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.18%
Total annual fund operating expenses rr_ExpensesOverAssets 1.12%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 114
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 356
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 617
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,363
1 Year rr_AverageAnnualReturnYear01 28.38%
5 Years rr_AverageAnnualReturnYear05 11.30%
10 Years rr_AverageAnnualReturnYear10 4.29%
Putnam VT Global Equity Fund | MSCI World Index (ND) (no deduction for fees expenses or taxes, other than withholding taxes on reinvested dividends)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 22.40%
5 Years rr_AverageAnnualReturnYear05 11.64%
10 Years rr_AverageAnnualReturnYear10 5.03%
Putnam VT Global Health Care Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Global Health Care Fund seeks capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 60%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 60.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock For this non-diversified fund concentrating in the health care industries, we invest mainly in common stocks (growth or value stocks or both) of large and midsize companies worldwide that we believe have favorable investment potential. Under normal circumstances, we invest at least 80% of the fund’s net assets in securities of companies in the health care industries. This policy may be changed only after 60 days’ notice to shareholders. Potential investments include companies that manufacture health care supplies or provide health care-related services, and companies in the research, development, production and marketing of pharmaceuticals and biotechnology products. We may purchase stocks of companies with stock prices that reflect a value lower than that which we place on the company. We may also consider other factors that we believe will cause the stock price to rise. We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments. We may also use derivatives, such as futures, options, certain foreign currency transactions, warrants and swap contracts, for both hedging and non-hedging purposes, and may engage in short sales of securities.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. 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. The health care industries may be affected by technological obsolescence, changes in regulatory approval policies for drugs, medical devices or procedures and changes in governmental and private payment systems. Our policy of concentrating on a limited group of industries and the fund’s “non-diversified” status, which means the fund may invest a greater percentage of its assets in fewer issuers than a “diversified fund,” can increase the fund’s vulnerability to adverse developments affecting a single industry or issuer, which may result in greater losses and volatility for the fund. The value of international investments traded in foreign currencies may be adversely impacted by fluctuations in exchange rates. International investments, particularly investments in emerging markets, may carry risks associated with potentially less stable economies or governments (such as the risk of seizure by a foreign government, the imposition of currency or other restrictions, or high levels of inflation or deflation), and may be or become illiquid. Our use of derivatives may increase the risks of investing in the fund by increasing investment exposure (which may be considered leverage) or, in the case of many over-the-counter instruments, because of the potential inability to terminate or sell derivatives positions and the potential failure of the other party to the instrument to meet its obligations. Our use of short selling may result in losses if the securities appreciate in value.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Nondiversified Status [Text] rr_RiskNondiversifiedStatus Our policy of concentrating on a limited group of industries and the fund’s “non-diversified” status, which means the fund may invest a greater percentage of its assets in fewer issuers than a “diversified fund,” can increase the fund’s vulnerability to adverse developments affecting a single industry or issuer, which may result in greater losses and volatility for the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18  −0.15%

Best calendar quarter
Q1 2013   13.10%

Worst calendar quarter
Q3 2011 −17.93%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (0.15%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2013
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 13.10%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (17.93%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Putnam VT Global Health Care Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.62%
Other expenses rr_OtherExpensesOverAssets 0.16%
Total annual fund operating expenses rr_ExpensesOverAssets 0.78%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 80
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 249
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 433
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 966
Annual Return 2008 rr_AnnualReturn2008 (16.90%)
Annual Return 2009 rr_AnnualReturn2009 26.46%
Annual Return 2010 rr_AnnualReturn2010 2.67%
Annual Return 2011 rr_AnnualReturn2011 (0.89%)
Annual Return 2012 rr_AnnualReturn2012 22.57%
Annual Return 2013 rr_AnnualReturn2013 41.98%
Annual Return 2014 rr_AnnualReturn2014 27.96%
Annual Return 2015 rr_AnnualReturn2015 8.06%
Annual Return 2016 rr_AnnualReturn2016 (11.14%)
Annual Return 2017 rr_AnnualReturn2017 15.60%
1 Year rr_AverageAnnualReturnYear01 15.60%
5 Years rr_AverageAnnualReturnYear05 15.06%
10 Years rr_AverageAnnualReturnYear10 10.21%
Putnam VT Global Health Care Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.62%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.16%
Total annual fund operating expenses rr_ExpensesOverAssets 1.03%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 105
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 328
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 569
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,259
1 Year rr_AverageAnnualReturnYear01 15.30%
5 Years rr_AverageAnnualReturnYear05 14.78%
10 Years rr_AverageAnnualReturnYear10 9.94%
Putnam VT Global Health Care Fund | MSCI World Health Care Index (ND) (no deduction for fees expenses or taxes, other than withholding taxes on reinvested dividends)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 19.80%
5 Years rr_AverageAnnualReturnYear05 13.88%
10 Years rr_AverageAnnualReturnYear10 8.94%
Putnam VT Global Utilities Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Global Utilities Fund seeks capital growth and current income.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 43%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 43.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock For this non-diversified fund concentrating in the utilities industries, we invest mainly in common stocks (growth or value stocks or both) of large and midsize companies worldwide that we believe have favorable investment potential. Under normal circumstances, we invest at least 80% of the fund’s net assets in securities of companies worldwide in the utilities industries. This policy may be changed only after 60 days’ notice to shareholders.

Potential investments include electric, gas or water utilities and companies that operate as independent producers and/or distributors of power. We may purchase stocks of companies with stock prices that reflect a value lower than that which we place on the company. We may also consider other factors that we believe will cause the stock price to rise. We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments. We may also use derivatives, such as futures, options, certain foreign currency transactions, warrants and swap contracts, for both hedging and non-hedging purposes, and may engage in short sales of securities.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings.

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. The utilities industries may be affected by increases in fuel costs, technological obsolescence, changes in regulatory policies and deregulation. Our policy of concentrating on a limited group of industries and the fund’s “non-diversified” status, which means the fund may invest a greater percentage of its assets in fewer issuers than a “diversified fund,” can increase the fund’s vulnerability to adverse developments affecting a single industry or issuer, which may result in greater losses and volatility for the fund. The value of international investments traded in foreign currencies may be adversely impacted by fluctuations in exchange rates. International investments, particularly investments in emerging markets, may carry risks associated with potentially less stable economies or governments (such as the risk of seizure by a foreign government, the imposition of currency or other restrictions, or high levels of inflation or deflation), and may be or become illiquid. Our use of derivatives may increase the risks of investing in the fund by increasing investment exposure (which may be considered leverage) or, in the case of many over-the-counter instruments, because of the potential inability to terminate or sell derivatives positions and the potential failure of the other party to the instrument to meet its obligations. Our use of short selling may result in losses if the securities appreciate in value.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Nondiversified Status [Text] rr_RiskNondiversifiedStatus Our policy of concentrating on a limited group of industries and the fund’s “non-diversified” status, which means the fund may invest a greater percentage of its assets in fewer issuers than a “diversified fund,” can increase the fund’s vulnerability to adverse developments affecting a single industry or issuer, which may result in greater losses and volatility for the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18  −2.63%

Best calendar quarter
Q2 2009   14.09%

Worst calendar quarter
Q3 2008 −19.64%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (2.63%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 14.09%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (19.64%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Putnam VT Global Utilities Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.62%
Other expenses rr_OtherExpensesOverAssets 0.20%
Total annual fund operating expenses rr_ExpensesOverAssets 0.82%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 84
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 262
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 455
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,014
Annual Return 2008 rr_AnnualReturn2008 (30.33%)
Annual Return 2009 rr_AnnualReturn2009 7.66%
Annual Return 2010 rr_AnnualReturn2010 2.10%
Annual Return 2011 rr_AnnualReturn2011 (5.19%)
Annual Return 2012 rr_AnnualReturn2012 5.35%
Annual Return 2013 rr_AnnualReturn2013 14.02%
Annual Return 2014 rr_AnnualReturn2014 14.88%
Annual Return 2015 rr_AnnualReturn2015 (9.65%)
Annual Return 2016 rr_AnnualReturn2016 2.19%
Annual Return 2017 rr_AnnualReturn2017 22.43%
1 Year rr_AverageAnnualReturnYear01 22.43%
5 Years rr_AverageAnnualReturnYear05 8.17%
10 Years rr_AverageAnnualReturnYear10 1.25%
Putnam VT Global Utilities Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.62%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.20%
Total annual fund operating expenses rr_ExpensesOverAssets 1.07%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 109
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 340
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 590
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,306
1 Year rr_AverageAnnualReturnYear01 22.17%
5 Years rr_AverageAnnualReturnYear05 7.92%
10 Years rr_AverageAnnualReturnYear10 1.00%
Putnam VT Global Utilities Fund | MSCI World Utilities Index (ND) (no deduction for fees expenses or taxes, other than withholding taxes on reinvested dividends)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 13.66%
5 Years rr_AverageAnnualReturnYear05 7.86%
10 Years rr_AverageAnnualReturnYear10 0.66%
Putnam VT Government Money Market Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Government Money Market Fund seeks as high a rate of current income as Putnam Investment Management, LLC believes is consistent with preservation of capital and maintenance of liquidity.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest at least 99.5 percent of the fund’s total assets in cash, U.S. government securities and repurchase agreements that are fully collateralized by U.S. government securities or cash. We invest mainly in debt securities that are obligations of the U.S. government, its agencies and instrumentalities and accordingly are backed by the full faith and credit of the United States (e.g., U.S. Treasury bills) or by the credit of a federal agency or government-sponsored entity (e.g., Fannie Mae and Freddie Mac mortgage-backed bonds). The U.S. government securities in which we invest may also include variable and floating rate instruments and when-issued and delayed delivery securities (i.e., payment or delivery of the securities occurs at a future date for a predetermined price). Under normal circumstances, we invest at least 80% of the fund’s net assets in U.S. government securities and repurchase agreements that are fully collateralized by U.S. government securities. This policy may be changed only after 60 days’ notice to shareholders. The securities purchased by the fund are subject to quality, maturity, diversification and other requirements pursuant to rules promulgated by the Securities and Exchange Commission. We may consider, among other factors, credit and interest rate risks, as well as general market conditions, when deciding whether to buy or sell investments.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock The values of money market investments usually rise and fall in response to changes in interest rates. Interest rate risk is generally lowest for investments with short maturities (a significant part of the fund’s investments). Changes in the financial condition of an issuer or counterparty, changes in specific economic or political conditions that affect a particular type of issuer, and changes in general economic or political conditions can increase the risk of default by an issuer or counterparty, which can affect a security’s or instrument’s credit quality or value. Certain securities in which the fund may invest, including securities issued by certain U.S. government agencies and U.S. government sponsored enterprises, are not guaranteed by the U.S. government or supported by the full faith and credit of the United States. Mortgage-backed investments carry the risk that they may increase in value less when interest rates decline and decline in value more when interest rates rise. We may have to invest the proceeds from prepaid investments, including mortgage- and asset-backed investments, in other investments with less attractive terms and yields.

The fund may not achieve its goal, and is not intended to be a complete investment program. You could lose money by investing in the fund. Although the fund seeks to preserve the value of your investment at $1.00 per share it cannot guarantee it will do so. An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The fund’s sponsor has no legal obligation to provide financial support to the fund, and you should not expect that the sponsor will provide financial support to the fund at any time.
Risk Lose Money [Text] rr_RiskLoseMoney You could lose money by investing in the fund.
Risk Money Market Fund [Text] rr_RiskMoneyMarketFund Although the fund seeks to preserve the value of your investment at $1.00 per share it cannot guarantee it will do so.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The fund’s sponsor has no legal obligation to provide financial support to the fund, and you should not expect that the sponsor will provide financial support to the fund at any time.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   0.25%

Best calendar quarter
Q1 2008   0.95%

Worst calendar quarter
Q3 2016  0.00%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 0.25%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2008
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 0.95%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2016
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn none
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock Effective April 30, 2016, Putnam VT Money Market Fund was renamed Putnam VT Government Money Market Fund. Performance for periods prior to April 30, 2016 is based on the fund’s prior investment strategy, which allowed the fund to invest in a broader range of money market securities.
Putnam VT Government Money Market Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.28%
Other expenses rr_OtherExpensesOverAssets 0.17%
Total annual fund operating expenses rr_ExpensesOverAssets 0.45%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 46
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 144
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 252
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 567
Annual Return 2008 rr_AnnualReturn2008 2.83%
Annual Return 2009 rr_AnnualReturn2009 0.35%
Annual Return 2010 rr_AnnualReturn2010 0.04%
Annual Return 2011 rr_AnnualReturn2011 0.01%
Annual Return 2012 rr_AnnualReturn2012 0.01%
Annual Return 2013 rr_AnnualReturn2013 0.01%
Annual Return 2014 rr_AnnualReturn2014 0.01%
Annual Return 2015 rr_AnnualReturn2015 0.01%
Annual Return 2016 rr_AnnualReturn2016 0.01%
Annual Return 2017 rr_AnnualReturn2017 0.47%
1 Year rr_AverageAnnualReturnYear01 0.47%
5 Years rr_AverageAnnualReturnYear05 0.10%
10 Years rr_AverageAnnualReturnYear10 0.37%
Putnam VT Government Money Market Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.28%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.17%
Total annual fund operating expenses rr_ExpensesOverAssets 0.70%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 72
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 224
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 390
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 871
1 Year rr_AverageAnnualReturnYear01 0.24%
5 Years rr_AverageAnnualReturnYear05 0.06%
10 Years rr_AverageAnnualReturnYear10 0.31%
Putnam VT Growth Opportunities Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Growth Opportunities Fund seeks capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 59%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 59.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in common stocks of large U.S. companies, with a focus on growth stocks. Growth stocks are issued by companies whose earnings are expected to grow faster than those of similar firms, and whose business growth and other characteristics may lead to an increase in stock price. We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer, industry or sector. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. Growth stocks may be more susceptible to earnings disappointments, and the market may not favor growth-style investing. From time to time, the fund may invest a significant portion of its assets in companies in one or more related industries or sectors, which may make the fund more vulnerable to adverse developments affecting those industries or sectors.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   3.02%

Best calendar quarter
Q1 2012   18.22%

Worst calendar quarter
Q4 2008 −21.27%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 3.02%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2012
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.22%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (21.27%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Putnam VT Growth Opportunities Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.55%
Other expenses rr_OtherExpensesOverAssets 0.11%
Total annual fund operating expenses rr_ExpensesOverAssets 0.66%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 67
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 211
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 368
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 822
Annual Return 2008 rr_AnnualReturn2008 (37.63%)
Annual Return 2009 rr_AnnualReturn2009 41.26%
Annual Return 2010 rr_AnnualReturn2010 17.57%
Annual Return 2011 rr_AnnualReturn2011 (3.86%)
Annual Return 2012 rr_AnnualReturn2012 17.85%
Annual Return 2013 rr_AnnualReturn2013 36.55%
Annual Return 2014 rr_AnnualReturn2014 14.16%
Annual Return 2015 rr_AnnualReturn2015 1.28%
Annual Return 2016 rr_AnnualReturn2016 6.72%
Annual Return 2017 rr_AnnualReturn2017 31.30%
1 Year rr_AverageAnnualReturnYear01 31.30%
5 Years rr_AverageAnnualReturnYear05 17.21%
10 Years rr_AverageAnnualReturnYear10 10.01%
Putnam VT Growth Opportunities Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.55%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.11%
Total annual fund operating expenses rr_ExpensesOverAssets 0.91%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 93
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 290
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 504
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,120
1 Year rr_AverageAnnualReturnYear01 30.90%
5 Years rr_AverageAnnualReturnYear05 16.91%
10 Years rr_AverageAnnualReturnYear10 9.73%
Putnam VT Growth Opportunities Fund | Russell 1000 Growth Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 30.21% [2]
5 Years rr_AverageAnnualReturnYear05 17.33% [2]
10 Years rr_AverageAnnualReturnYear10 10.00% [2]
Putnam VT High Yield Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT High Yield Fund seeks high current income.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock Capital growth is a secondary goal when consistent with achieving high current income.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 43%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 43.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in bonds that are obligations of U.S. companies, are below investment-grade in quality (sometimes referred to as “junk bonds”), and have intermediate- to long-term maturities (three years or longer). Under normal circumstances, we invest at least 80% of the fund’s net assets in securities rated below investment-grade. This policy may be changed only after 60 days’ notice to shareholders. We may also invest in other debt instruments, including loans. We may consider, among other factors, credit, interest rate and prepayment risks, as well as general market conditions, when deciding whether to buy or sell investments. We may also use derivatives, such as futures, options, certain foreign currency transactions and swap contracts, for both hedging and non-hedging purposes.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of bonds in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions (including perceptions about the risk of default and expectations about monetary policy or interest rates), changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. The risks associated with bond investments include interest rate risk, which means the value of the fund’s investments is likely to fall if interest rates rise. Bond investments are also subject to credit risk, which is the risk that the issuer of a bond may default on payment of interest or principal. Interest rate risk is generally greater for longer-term bonds, and credit risk is generally greater for below-investment-grade bonds (a significant part of the fund’s investments). Our use of derivatives may increase the risks of investing in the fund by increasing investment exposure (which may be considered leverage) or, in the case of many over-the-counter instruments, because of the potential inability to terminate or sell derivatives positions and the potential failure of the other party to the instrument to meet its obligations.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   −0.83%

Best calendar quarter
Q2 2009  18.84%

Worst calendar quarter
Q4 2008 −19.22%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (0.83%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2012
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.84%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (19.22%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Putnam VT High Yield Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.56%
Other expenses rr_OtherExpensesOverAssets 0.16%
Total annual fund operating expenses rr_ExpensesOverAssets 0.72%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 74
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 230
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 401
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 894
Annual Return 2008 rr_AnnualReturn2008 (26.20%)
Annual Return 2009 rr_AnnualReturn2009 50.91%
Annual Return 2010 rr_AnnualReturn2010 14.54%
Annual Return 2011 rr_AnnualReturn2011 1.85%
Annual Return 2012 rr_AnnualReturn2012 16.34%
Annual Return 2013 rr_AnnualReturn2013 8.10%
Annual Return 2014 rr_AnnualReturn2014 1.91%
Annual Return 2015 rr_AnnualReturn2015 (5.14%)
Annual Return 2016 rr_AnnualReturn2016 15.66%
Annual Return 2017 rr_AnnualReturn2017 7.22%
1 Year rr_AverageAnnualReturnYear01 7.22%
5 Years rr_AverageAnnualReturnYear05 5.32%
10 Years rr_AverageAnnualReturnYear10 6.95%
Putnam VT High Yield Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.56%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.16%
Total annual fund operating expenses rr_ExpensesOverAssets 0.97%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 99
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 309
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 536
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,190
1 Year rr_AverageAnnualReturnYear01 6.98%
5 Years rr_AverageAnnualReturnYear05 5.09%
10 Years rr_AverageAnnualReturnYear10 6.72%
Putnam VT High Yield Fund | JPMorgan Developed High Yield Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 7.80%
5 Years rr_AverageAnnualReturnYear05 6.15%
10 Years rr_AverageAnnualReturnYear10 8.29%
Putnam VT Income Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Income Fund seeks high current income consistent with what Putnam Investment Management, LLC believes to be prudent risk.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 848%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 848.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in bonds that are securitized debt instruments (such as mortgage-backed investments) and other obligations of companies and governments worldwide denominated in U.S. dollars, are either investment-grade or below-investment-grade in quality (sometimes referred to as “junk bonds”) and have intermediate- to long-term maturities (three years or longer). We may consider, among other factors, credit, interest rate and prepayment risks, as well as general market conditions, when deciding whether to buy or sell investments. We typically use to a significant extent derivatives, such as futures, options and swap contracts, for both hedging and non-hedging purposes.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of bonds in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions (including perceptions about the risk of default and expectations about monetary policy or interest rates), changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. The risks associated with bond investments include interest rate risk, which means the value of the fund’s investments is likely to fall if interest rates rise. Bond investments are also subject to credit risk, which is the risk that the issuer of a bond may default on payment of interest or principal. Interest rate risk is generally greater for longer-term bonds, and credit risk is generally greater for below-investment-grade bonds (a significant part of the fund’s investments). Mortgage-backed investments, unlike traditional debt investments, are also subject to prepayment risk, which means that they may increase in value less than other bonds when interest rates decline and decline in value more than other bonds when interest rates rise. We may have to invest the proceeds from prepaid investments, including mortgage-backed investments, in other investments with less attractive terms and yields.

Our use of derivatives may increase the risks of investing in the fund by increasing investment exposure (which may be considered leverage) or, in the case of many over-the-counter instruments, because of the potential inability to terminate or sell derivatives positions and the potential failure of the other party to the instrument to meet its obligations.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   −0.47%

Best calendar quarter
Q2 2009  14.35%

Worst calendar quarter
Q4 2008 −17.63%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (0.47%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 14.35%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (17.63%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Putnam VT Income Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.39%
Other expenses rr_OtherExpensesOverAssets 0.19%
Total annual fund operating expenses rr_ExpensesOverAssets 0.58%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 59
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 186
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 324
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 726
Annual Return 2008 rr_AnnualReturn2008 (23.78%)
Annual Return 2009 rr_AnnualReturn2009 47.22%
Annual Return 2010 rr_AnnualReturn2010 10.22%
Annual Return 2011 rr_AnnualReturn2011 5.16%
Annual Return 2012 rr_AnnualReturn2012 11.06%
Annual Return 2013 rr_AnnualReturn2013 2.13%
Annual Return 2014 rr_AnnualReturn2014 6.68%
Annual Return 2015 rr_AnnualReturn2015 (1.19%)
Annual Return 2016 rr_AnnualReturn2016 2.27%
Annual Return 2017 rr_AnnualReturn2017 5.90%
1 Year rr_AverageAnnualReturnYear01 5.90%
5 Years rr_AverageAnnualReturnYear05 3.12%
10 Years rr_AverageAnnualReturnYear10 5.35%
Putnam VT Income Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.39%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.19%
Total annual fund operating expenses rr_ExpensesOverAssets 0.83%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 85
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 265
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 460
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,025
1 Year rr_AverageAnnualReturnYear01 5.59%
5 Years rr_AverageAnnualReturnYear05 2.85%
10 Years rr_AverageAnnualReturnYear10 5.07%
Putnam VT Income Fund | Bloomberg Barclays U.S. Aggregate Bond Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 3.54%
5 Years rr_AverageAnnualReturnYear05 2.10%
10 Years rr_AverageAnnualReturnYear10 4.01%
Putnam VT International Equity Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT International Equity Fund seeks capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 61%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 61.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in common stocks (growth or value stocks or both) of large and midsize companies outside the United States that we believe have favorable investment potential. For example, we may purchase stocks of companies with stock prices that reflect a value lower than that which we place on the company. Under normal circumstances, we invest at least 80% of the fund’s net assets in equity investments. This policy may be changed only after 60 days’ notice to shareholders. We may also consider other factors that we believe will cause the stock price to rise. We invest mainly in developed countries, but may invest in emerging markets. We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments. We may also use derivatives, such as futures, options, certain foreign currency transactions, warrants and swap contracts, for both hedging and non-hedging purposes.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. 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. The value of international investments traded in foreign currencies may be adversely impacted by fluctuations in exchange rates. International investments, particularly investments in emerging markets, may carry risks associated with potentially less stable economies or governments (such as the risk of seizure by a foreign government, the imposition of currency or other restrictions, or high levels of inflation or deflation), and may be or become illiquid.

Our use of derivatives may increase the risks of investing in the fund by increasing investment exposure (which may be considered leverage) or, in the case of many over-the-counter instruments, because of the potential inability to terminate or sell derivatives positions and the potential failure of the other party to the instrument to meet its obligations.

Investments focused in a single region may be affected by common economic forces and other factors. In addition, events in any one country within the region may impact the other countries or the region as a whole. Because the fund currently, and may in the future, invests significantly in European companies, the fund is particularly susceptible to economic, political, regulatory or other events or conditions affecting issuers in Europe. European financial markets have in recent years experienced increased volatility due to concerns with some countries’ high levels of sovereign debt, budget deficits, and unemployment.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   −0.05%

Best calendar quarter
Q2 2009  22.55%

Worst calendar quarter
Q3 2011 −24.07%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (0.05%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 22.55%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (24.07%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Putnam VT International Equity Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.69%
Other expenses rr_OtherExpensesOverAssets 0.15%
Total annual fund operating expenses rr_ExpensesOverAssets 0.84%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 86
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 268
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 466
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,037
Annual Return 2008 rr_AnnualReturn2008 (43.84%)
Annual Return 2009 rr_AnnualReturn2009 25.00%
Annual Return 2010 rr_AnnualReturn2010 10.27%
Annual Return 2011 rr_AnnualReturn2011 (16.71%)
Annual Return 2012 rr_AnnualReturn2012 22.21%
Annual Return 2013 rr_AnnualReturn2013 28.44%
Annual Return 2014 rr_AnnualReturn2014 (6.58%)
Annual Return 2015 rr_AnnualReturn2015 0.41%
Annual Return 2016 rr_AnnualReturn2016 (2.21%)
Annual Return 2017 rr_AnnualReturn2017 26.93%
1 Year rr_AverageAnnualReturnYear01 26.93%
5 Years rr_AverageAnnualReturnYear05 8.38%
10 Years rr_AverageAnnualReturnYear10 1.66%
Putnam VT International Equity Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.69%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.15%
Total annual fund operating expenses rr_ExpensesOverAssets 1.09%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 111
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 347
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 601
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,329
1 Year rr_AverageAnnualReturnYear01 26.58%
5 Years rr_AverageAnnualReturnYear05 8.10%
10 Years rr_AverageAnnualReturnYear10 1.40%
Putnam VT International Equity Fund | MSCI EAFE Index (ND) (no deduction for fees, expenses or taxes, other than withholding taxes on reinvested dividends)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 25.03%
5 Years rr_AverageAnnualReturnYear05 7.90%
10 Years rr_AverageAnnualReturnYear10 1.94%
Putnam VT International Growth Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT International Growth Fund seeks long-term capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 4/30/19
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 105%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 105.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Only the first year of each period in the example takes into account the expense reimbursement described above. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in common stocks of companies of any size in established and emerging markets outside the United States. We invest mainly in growth stocks, which are issued by companies whose earnings are expected to grow faster than those of similar firms, and whose business growth and other characteristics may lead to an increase in stock price. We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments. We may also use derivatives, such as futures, options, certain foreign currency transactions, warrants and swap contracts, for both hedging and non-hedging purposes.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund's portfolio holdings. Growth stocks may be more susceptible to earnings disappointments, and the market may not favor growth-style investing. These risks are generally greater for small and midsize companies. The value of international investments traded in foreign currencies may be adversely impacted by fluctuations in exchange rates. International investments, particularly investments in emerging markets, may carry risks associated with potentially less stable economies or governments (such as the risk of seizure by a foreign government, the imposition of currency or other restrictions, or high levels of inflation or deflation), and may be or become illiquid. Our use of derivatives may increase the risks of investing in the fund by increasing investment exposure (which may be considered leverage) or, in the case of many over-the-counter instruments, because of the potential inability to terminate or sell derivatives positions and the potential failure of the other party to the instrument to meet its obligations.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   1.46%

Best calendar quarter
Q2 2009  23.00%

Worst calendar quarter
Q3 2011 −24.72%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 1.46%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 23.00%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (24.72%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Putnam VT International Growth Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.92%
Other expenses rr_OtherExpensesOverAssets 0.42%
Total annual fund operating expenses rr_ExpensesOverAssets 1.34%
Expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.14%) [1]
Total annual fund operating expenses after expense reimbursement rr_NetExpensesOverAssets 1.20%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 122
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 411
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 721
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,600
Annual Return 2008 rr_AnnualReturn2008 (42.37%)
Annual Return 2009 rr_AnnualReturn2009 38.76%
Annual Return 2010 rr_AnnualReturn2010 12.49%
Annual Return 2011 rr_AnnualReturn2011 (17.65%)
Annual Return 2012 rr_AnnualReturn2012 21.24%
Annual Return 2013 rr_AnnualReturn2013 22.70%
Annual Return 2014 rr_AnnualReturn2014 (5.90%)
Annual Return 2015 rr_AnnualReturn2015 1.33%
Annual Return 2016 rr_AnnualReturn2016 (6.46%)
Annual Return 2017 rr_AnnualReturn2017 35.37%
1 Year rr_AverageAnnualReturnYear01 35.37%
5 Years rr_AverageAnnualReturnYear05 8.18%
10 Years rr_AverageAnnualReturnYear10 2.90%
Putnam VT International Growth Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.92%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.42%
Total annual fund operating expenses rr_ExpensesOverAssets 1.59%
Expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.14%) [1]
Total annual fund operating expenses after expense reimbursement rr_NetExpensesOverAssets 1.45%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 148
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 488
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 852
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,877
1 Year rr_AverageAnnualReturnYear01 35.04%
5 Years rr_AverageAnnualReturnYear05 7.91%
10 Years rr_AverageAnnualReturnYear10 2.64%
Putnam VT International Growth Fund | MSCI EAFE Growth Index (ND) (no deduction for fees, expenses or taxes, other than withholding taxes on reinvested dividends)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 28.86%
5 Years rr_AverageAnnualReturnYear05 8.78%
10 Years rr_AverageAnnualReturnYear10 2.67%
Putnam VT International Value Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT International Value Fund seeks capital growth.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock Current income is a secondary objective.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 11%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 11.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in common stocks of large and midsize companies outside the United States, with a focus on value stocks. Value stocks are those that we believe are currently undervalued by the market. If we are correct and other investors ultimately recognize the value of the company, the price of its stock may rise. We invest mainly in developed countries, but may invest in emerging markets. We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments. We may also use derivatives, such as futures, options, certain foreign currency transactions, warrants and swap contracts, for both hedging and non-hedging purposes.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer, industry or sector. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. Value stocks may fail to rebound, and the market may not favor value-style investing. These risks are generally greater for small and midsize companies. From time to time, the fund may invest a significant portion of its assets in companies in one or more related industries or sectors, which would make the fund more vulnerable to adverse developments affecting those industries or sectors.

The value of international investments traded in foreign currencies may be adversely impacted by fluctuations in exchange rates. International investments, particularly investments in emerging markets, may carry risks associated with potentially less stable economies or governments (such as the risk of seizure by a foreign government, the imposition of currency or other restrictions, or high levels of inflation or deflation), and may be or become illiquid. Investments focused in a single region may be affected by common economic forces and other factors. In addition, events in any one country within the region may impact the other countries or the region as a whole. Because the fund currently, and may in the future, invests significantly in European companies, the fund is particularly susceptible to economic, political, regulatory or other events or conditions affecting issuers in Europe. European financial markets have in recent years experienced increased volatility due to concerns with some countries’ high levels of sovereign debt, budget deficits, and unemployment.

Our use of derivatives may increase the risks of investing in the fund by increasing investment exposure (which may be considered leverage) or, in the case of many over-the-counter instruments, because of the potential inability to terminate or sell derivatives positions and the potential failure of the other party to the instrument to meet its obligations.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   −1.24%

Best calendar quarter
Q2 2009  23.79%

Worst calendar quarter
Q4 2008 −23.24%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (1.24%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 23.79%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (23.24%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Putnam VT International Value Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.69%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 0.90%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 92
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 287
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 498
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,108
Annual Return 2008 rr_AnnualReturn2008 (45.85%)
Annual Return 2009 rr_AnnualReturn2009 26.39%
Annual Return 2010 rr_AnnualReturn2010 7.42%
Annual Return 2011 rr_AnnualReturn2011 (13.52%)
Annual Return 2012 rr_AnnualReturn2012 21.80%
Annual Return 2013 rr_AnnualReturn2013 22.63%
Annual Return 2014 rr_AnnualReturn2014 (9.29%)
Annual Return 2015 rr_AnnualReturn2015 (1.71%)
Annual Return 2016 rr_AnnualReturn2016 1.28%
Annual Return 2017 rr_AnnualReturn2017 24.95%
1 Year rr_AverageAnnualReturnYear01 24.95%
5 Years rr_AverageAnnualReturnYear05 6.71%
10 Years rr_AverageAnnualReturnYear10 0.69%
Putnam VT International Value Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.69%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 1.15%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 117
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 365
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 633
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,398
1 Year rr_AverageAnnualReturnYear01 24.69%
5 Years rr_AverageAnnualReturnYear05 6.45%
10 Years rr_AverageAnnualReturnYear10 0.46%
Putnam VT International Value Fund | MSCI EAFE Value Index (ND)  (no deduction for fees, expenses or taxes, other than withholding taxes on reinvested dividends)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 21.44%
5 Years rr_AverageAnnualReturnYear05 6.95%
10 Years rr_AverageAnnualReturnYear10 1.15%
Putnam VT Investors Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Investors Fund seeks long-term growth of capital and any increased income that results from this growth.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 51%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 51.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in common stocks (growth or value stocks or both) of large U.S. companies that we believe have favorable investment potential. For example, we may purchase stocks of companies with stock prices that reflect a value lower than that which we place on the company. We may also consider other factors we believe will cause the stock price to rise. We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. Growth stocks may be more susceptible to earnings disappointments, and value stocks may fail to rebound.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   −0.77%

Best calendar quarter
Q2 2009  18.61%

Worst calendar quarter
Q4 2008 −21.46%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (0.77%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.61%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (21.46%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Putnam VT Investors Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.55%
Other expenses rr_OtherExpensesOverAssets 0.13%
Total annual fund operating expenses rr_ExpensesOverAssets 0.68%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 69
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 218
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 379
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 847
Annual Return 2008 rr_AnnualReturn2008 (39.44%)
Annual Return 2009 rr_AnnualReturn2009 31.18%
Annual Return 2010 rr_AnnualReturn2010 14.24%
Annual Return 2011 rr_AnnualReturn2011 0.29%
Annual Return 2012 rr_AnnualReturn2012 17.06%
Annual Return 2013 rr_AnnualReturn2013 35.52%
Annual Return 2014 rr_AnnualReturn2014 14.25%
Annual Return 2015 rr_AnnualReturn2015 (1.96%)
Annual Return 2016 rr_AnnualReturn2016 12.34%
Annual Return 2017 rr_AnnualReturn2017 23.14%
1 Year rr_AverageAnnualReturnYear01 23.14%
5 Years rr_AverageAnnualReturnYear05 16.00%
10 Years rr_AverageAnnualReturnYear10 8.39%
Putnam VT Investors Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.55%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.13%
Total annual fund operating expenses rr_ExpensesOverAssets 0.93%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 95
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 296
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 515
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,143
1 Year rr_AverageAnnualReturnYear01 22.86%
5 Years rr_AverageAnnualReturnYear05 15.69%
10 Years rr_AverageAnnualReturnYear10 8.12%
Putnam VT Investors Fund | S&P 500 Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 21.83%
5 Years rr_AverageAnnualReturnYear05 15.79%
10 Years rr_AverageAnnualReturnYear10 8.50%
Putnam VT Mortgage Securities Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading *Prior to April 30, 2018, the fund was known as Putnam VT American Government Income Fund.

Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Mortgage Securities Fund seeks as high a level of current income as Putnam Management believes is consistent with preservation of capital.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 4/30/19
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 1,188%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 1188.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Only the first year of each period in the example takes into account the expense reimbursement described above. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in mortgages, mortgage-related fixed income securities and related derivatives that are either investment-grade or below-investment-grade in quality (sometimes referred to as “junk bonds”). Under normal circumstances, we invest at least 80% of the fund’s net assets (plus any borrowings for investment purposes) in mortgages, mortgage-related fixed income securities and related derivatives (i.e., derivatives used to acquire exposure to, or whose underlying securities are, mortgages or mortgage-related securities). The fund generally uses the net unrealized gain or loss, or market value, of mortgage-related derivatives for purposes of this policy, but may use the notional value of a derivative if that is determined to be a more appropriate measure of the fund’s investment exposure. This policy may be changed only after 60 days’ notice to shareholders.

We expect to invest in mortgage-backed investments that are obligations of U.S. government agencies and instrumentalities and accordingly are backed by the full faith and credit of the United States (e.g., Ginnie Mae mortgage-backed bonds) as well as in mortgage-backed investments that are backed by only the credit of a federal agency or government-sponsored entity (e.g., Fannie Mae and Freddie Mac mortgage-backed bonds), and that have short- to long-term maturities.

We also expect to invest in lower-rated, higher-yielding mortgage-backed securities, including non-agency residential mortgage-backed securities (which may be backed by non-qualified or “sub-prime” mortgages), commercial mortgage-backed securities and collateralized mortgage obligations (including interest only, principal only, and other prepayment derivatives). Non-agency (i.e., privately issued) securities typically are lower-rated and higher yielding than securities issued or backed by agencies such as Ginnie Mae, Fannie Mae or Freddie Mac. While our emphasis will be on mortgage-backed securities, we may also invest to a lesser extent in other types of asset-backed securities.

We may consider, among other factors, credit, interest rate, prepayment and liquidity risks, as well as general market conditions, when deciding whether to buy or sell investments.

We typically use to a significant extent derivatives, including interest rate swaps, swaptions, forward delivery contracts, total return swaps, and options on mortgage-backed securities and indices, for both hedging and non-hedging purposes, including to obtain or adjust exposure to mortgage-backed investments.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of bonds in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions (including perceptions about the risk of default and expectations about monetary policy or interest rates), changes in government intervention in the financial and housing markets, and factors related to a specific issuer, industry, geography, such as a region of the United States, or sector, such as the housing or real estate markets. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings.

The risks associated with bond investments include interest rate risk, which means the value of the fund’s investments is likely to fall if interest rates rise. Bond investments are also subject to credit risk, which is the risk that issuers of the fund’s investments may default on payment of interest or principal. Default risk is generally higher for non-qualified mortgages. Interest rate risk is generally greater for longer-term bonds, and credit risk is generally greater for below-investment grade bonds, which may be considered speculative. Mortgage- and asset-backed investments, unlike traditional debt investments, are also subject to prepayment risk, which means that they may increase in value less than other bonds when interest rates decline and decline in value more than other bonds when interest rates rise. We may have to invest the proceeds from prepaid investments, including mortgage- and asset-backed investments, in other investments with less attractive terms and yields. The fund’s investments in mortgage-backed securities and asset-backed securities, and in certain other securities and derivatives, may be or become illiquid. The fund’s exposure to privately issued mortgage-backed securities and mortgage-backed securities issued or guaranteed by the U.S. government or its agencies or instrumentalities may make the fund’s net asset value more susceptible to economic, market, political and other developments affecting the housing or real estate markets.

Our use of derivatives may increase the risks of investing in the fund by increasing investment exposure (which may be considered leverage) or, in the case of many over-the-counter instruments, because of the potential inability to terminate or sell derivatives positions and the potential failure of the other party to the instrument to meet its obligations. Our use of short selling may result in losses if the securities appreciate in value.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. Before April 30, 2018, the fund was managed with a materially different investment strategy and may have achieved materially different performance results under its current investment strategy from that shown for periods before this date. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   −0.30%

Best calendar quarter
Q1 2009  5.84%

Worst calendar quarter
Q3 2008 −2.70%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (0.30%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 5.84%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (2.70%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Performance Table Market Index Changed rr_PerformanceTableMarketIndexChanged

As of April 30, 2018, the Bloomberg Barclays U.S. MBS Index (an unmanaged index of agency mortgage backed pass-through securities (both fixed-rate and hybrid ARM) guaranteed by Ginnie Mae, Fannie Mae, and Freddie Mac) replaced the Bloomberg Barclays Government Bond Index (an unmanaged index of U.S. Treasury and agency securities) as the benchmark for this fund because, in Putnam Investment Management LLC's opinion, the securities tracked by this index more accurately reflect the types of securities that generally will be held by the fund. The average annual total returns of the Bloomberg Barclays Government Bond Index for the one-, five-, and ten-year periods ended on December 31, 2017 were 2.30%, 1.28% and 3.23%, respectively.
Putnam VT Mortgage Securities Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.39%
Other expenses rr_OtherExpensesOverAssets 0.27%
Total annual fund operating expenses rr_ExpensesOverAssets 0.66%
Expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.16%) [1]
Total annual fund operating expenses after expense reimbursement rr_NetExpensesOverAssets 0.50%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 51
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 195
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 352
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 807
Annual Return 2008 rr_AnnualReturn2008 0.54%
Annual Return 2009 rr_AnnualReturn2009 21.35%
Annual Return 2010 rr_AnnualReturn2010 5.35%
Annual Return 2011 rr_AnnualReturn2011 7.09%
Annual Return 2012 rr_AnnualReturn2012 2.16%
Annual Return 2013 rr_AnnualReturn2013 (0.19%)
Annual Return 2014 rr_AnnualReturn2014 4.49%
Annual Return 2015 rr_AnnualReturn2015 (0.33%)
Annual Return 2016 rr_AnnualReturn2016 0.36%
Annual Return 2017 rr_AnnualReturn2017 2.27%
1 Year rr_AverageAnnualReturnYear01 2.27%
5 Years rr_AverageAnnualReturnYear05 1.30%
10 Years rr_AverageAnnualReturnYear10 4.14%
Putnam VT Mortgage Securities Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.39%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.27%
Total annual fund operating expenses rr_ExpensesOverAssets 0.91%
Expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.16%) [1]
Total annual fund operating expenses after expense reimbursement rr_NetExpensesOverAssets 0.75%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 77
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 274
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 488
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,105
1 Year rr_AverageAnnualReturnYear01 1.96%
5 Years rr_AverageAnnualReturnYear05 1.05%
10 Years rr_AverageAnnualReturnYear10 3.88%
Putnam VT Mortgage Securities Fund | Bloomberg Barclays U.S. MBS Index (no deduction for fees or expenses)   
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 2.47% [4]
5 Years rr_AverageAnnualReturnYear05 2.04% [4]
10 Years rr_AverageAnnualReturnYear10 3.84% [4]
Putnam VT Mortgage Securities Fund | Bloomberg Barclays Government Bond-Bloomberg Barclays U.S. MBS Linked Benchmark (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 2.30% [5]
5 Years rr_AverageAnnualReturnYear05 1.28% [5]
10 Years rr_AverageAnnualReturnYear10 3.23% [5]
Putnam VT Multi-Asset Absolute Return Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading *Prior to April 30, 2018, the fund was known as Putnam VT Absolute Return 500 Fund.

Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Multi-Asset Absolute Return Fund seeks positive total return.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 4/30/19
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 576%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 576.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Only the first year of each period in the example takes into account the expense reimbursement described above. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock The fund is designed to pursue a consistent absolute return by combining two independent investment strategies — a beta strategy, which provides broad exposure to investment markets, and an alpha strategy, which seeks returns from active trading. The beta strategy seeks to balance risk and to provide positive total return by investing, without limit, in many different asset classes, including U.S., international, and emerging markets equity securities (growth or value stocks or both) and fixed-income securities; mortgage- and asset-backed securities; below-investment-grade securities (sometimes referred to as “junk bonds”); inflation-protected securities; commodities; and real estate investment trusts (REITs). The alpha strategy involves the potential use of active trading strategies designed to provide additional total return through active security selection, tactical asset allocation, currency transactions and options transactions. In pursuing a consistent absolute return, the fund’s strategies are also generally intended to produce lower volatility over a reasonable period of time than has been historically associated with traditional asset classes that have earned similar levels of return over long historical periods. These traditional asset classes might include, for example, equities or equity-like investments.

We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell equity investments, and, among other factors, credit, interest rate and prepayment risks when deciding whether to buy or sell fixed-income investments. We may also take into account general market conditions when making investment decisions. We typically use derivatives, such as futures, options, certain foreign currency transactions, warrants and swap contracts, to a significant extent for hedging purposes and to increase the fund’s exposure to the asset classes and strategies mentioned above, which may create investment leverage.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

Our allocation of assets among asset classes may hurt performance. The value of stocks and bonds in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions (including, in the case of bonds, perceptions about the risk of default and expectations about monetary policy or interest rates), changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. Growth stocks may be more susceptible to earnings disappointments, and value stocks may fail to rebound.

Bond investments are subject to interest rate risk, which means the value of the fund’s bond investments is likely to fall if interest rates rise. Bond investments also are subject to credit risk, which is the risk that the issuer of the bond may default on payment of interest or principal. Interest rate risk is generally greater for longer-term bonds, and credit risk is generally greater for below-investment-grade bonds, which may be considered speculative. Mortgage-backed investments, unlike traditional debt investments, are also subject to prepayment risk, which means that they may increase in value less than other bonds when interest rates decline and decline in value more than other bonds when interest rates rise. We may have to invest the proceeds from prepaid investments, including mortgage- and asset-backed investments, in other investments with less attractive terms and yields.

The value of international investments traded in foreign currencies may be adversely impacted by fluctuations in exchange rates. International investments, particularly investments in emerging markets, may carry risks associated with potentially less stable economies or governments (such as the risk of seizure by a foreign government, the imposition of currency or other restrictions, or high levels of inflation), and may be or become illiquid. Our alpha strategy may lose money or not earn a return sufficient to cover associated trading and other costs. Our use of leverage obtained through derivatives increases the risk of investing in the fund by increasing investment exposure. Derivatives also involve the risk, in the case of many over-the-counter instruments, of the potential inability to terminate or sell derivatives positions and the potential failure of the other party to the instrument to meet its obligations.

The fund may not achieve its goal, and it is not intended to be a complete investment program. The fund’s efforts to produce lower volatility returns may not be successful. An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. Before April 30, 2018, the fund was managed with a materially different investment strategy and may have achieved materially different performance results under its current strategy from that shown for periods before this date. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   −2.28%

Best calendar quarter
Q1 2012  4.57%

Worst calendar quarter
Q2 2013 −1.55%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (2.28%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2012
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 4.57%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Jun. 30, 2013
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (1.55%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock The Bloomberg Barclays U.S. Aggregate Bond Index and the S&P 500 Index are broad measures of market performance. Securities in the fund do not match those in the indexes and the performance of the fund will differ.

ICE BofAML Indexes: ICE Data Indices, LLC (“ICE BofAML”), used with permission. ICE BofAML permits use of the ICE BofAML indices and related data on an “as is” basis; makes no warranties regarding same; does not guarantee the suitability, quality, accuracy, timeliness, and/or completeness of the ICE BofAML indices or any data included in, related to, or derived therefrom; assumes no liability in connection with the use of the foregoing; and does not sponsor, endorse, or recommend Putnam Investments, or any of its products or services.

ICE BofAML U.S. Treasury Bill Index tracks the performance of U.S. dollar denominated U.S. Treasury bills, which represent obligations of the U.S. Government having a maturity of one year or less, and is intended as an approximate measure of the rate of inflation.
Putnam VT Multi-Asset Absolute Return Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.72%
Other expenses rr_OtherExpensesOverAssets 0.63%
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.04%
Total annual fund operating expenses rr_ExpensesOverAssets 1.39%
Expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.45%) [1]
Total annual fund operating expenses after expense reimbursement rr_NetExpensesOverAssets 0.94%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 96
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 396
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 718
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,630
Annual Return 2012 rr_AnnualReturn2012 4.57%
Annual Return 2013 rr_AnnualReturn2013 4.46%
Annual Return 2014 rr_AnnualReturn2014 4.12%
Annual Return 2015 rr_AnnualReturn2015 (0.22%)
Annual Return 2016 rr_AnnualReturn2016 0.93%
Annual Return 2017 rr_AnnualReturn2017 7.19%
1 Year rr_AverageAnnualReturnYear01 7.19%
5 Years rr_AverageAnnualReturnYear05 3.26%
Since Inception rr_AverageAnnualReturnSinceInception 2.54%
Inception Date rr_AverageAnnualReturnInceptionDate May 02, 2011
Putnam VT Multi-Asset Absolute Return Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.72%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.63%
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.04%
Total annual fund operating expenses rr_ExpensesOverAssets 1.64%
Expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.45%) [1]
Total annual fund operating expenses after expense reimbursement rr_NetExpensesOverAssets 1.19%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 121
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 473
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 849
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,906
1 Year rr_AverageAnnualReturnYear01 6.98%
5 Years rr_AverageAnnualReturnYear05 2.98%
Since Inception rr_AverageAnnualReturnSinceInception 2.27%
Inception Date rr_AverageAnnualReturnInceptionDate May 02, 2011
Putnam VT Multi-Asset Absolute Return Fund | S&P 500 Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 21.83%
5 Years rr_AverageAnnualReturnYear05 15.79%
Since Inception rr_AverageAnnualReturnSinceInception 13.00%
Inception Date rr_AverageAnnualReturnInceptionDate May 02, 2011
Putnam VT Multi-Asset Absolute Return Fund | Bloomberg Barclays U.S. Aggregate Bond Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 3.54%
5 Years rr_AverageAnnualReturnYear05 2.10%
Since Inception rr_AverageAnnualReturnSinceInception 3.10%
Inception Date rr_AverageAnnualReturnInceptionDate May 02, 2011
Putnam VT Multi-Asset Absolute Return Fund | ICE BofAML U.S. Treasury Bill Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 0.81%
5 Years rr_AverageAnnualReturnYear05 0.28%
Since Inception rr_AverageAnnualReturnSinceInception 0.24%
Inception Date rr_AverageAnnualReturnInceptionDate May 02, 2011
Putnam VT Multi-Asset Absolute Return Fund | ICE BofAML U.S. Treasury Bill Index plus 500 basis points (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 5.81%
5 Years rr_AverageAnnualReturnYear05 5.28%
Since Inception rr_AverageAnnualReturnSinceInception 5.24%
Inception Date rr_AverageAnnualReturnInceptionDate May 02, 2011
Putnam VT Research Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Research Fund seeks capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 94%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 94.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in common stocks (growth or value stocks or both) of large U.S. companies that we believe have favorable investment potential. For example, we may purchase stocks of companies with stock prices that reflect a value lower than that which we place on the company. We may also consider other factors we believe will cause the stock price to rise. We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. Growth stocks may be more susceptible to earnings disappointments, and value stocks may fail to rebound.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   −0.41%

Best calendar quarter
Q2 2009  18.46%

Worst calendar quarter
Q4 2008 −24.03%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (0.41%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.46%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (24.03%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Putnam VT Research Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.55%
Other expenses rr_OtherExpensesOverAssets 0.26%
Total annual fund operating expenses rr_ExpensesOverAssets 0.81%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 83
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 259
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 450
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,002
Annual Return 2008 rr_AnnualReturn2008 (38.42%)
Annual Return 2009 rr_AnnualReturn2009 33.54%
Annual Return 2010 rr_AnnualReturn2010 16.61%
Annual Return 2011 rr_AnnualReturn2011 (1.41%)
Annual Return 2012 rr_AnnualReturn2012 18.28%
Annual Return 2013 rr_AnnualReturn2013 33.60%
Annual Return 2014 rr_AnnualReturn2014 15.17%
Annual Return 2015 rr_AnnualReturn2015 (1.29%)
Annual Return 2016 rr_AnnualReturn2016 10.32%
Annual Return 2017 rr_AnnualReturn2017 23.70%
1 Year rr_AverageAnnualReturnYear01 23.70%
5 Years rr_AverageAnnualReturnYear05 15.69%
10 Years rr_AverageAnnualReturnYear10 8.77%
Putnam VT Research Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.55%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.26%
Total annual fund operating expenses rr_ExpensesOverAssets 1.06%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 108
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 337
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 585
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,294
1 Year rr_AverageAnnualReturnYear01 23.34%
5 Years rr_AverageAnnualReturnYear05 15.41%
10 Years rr_AverageAnnualReturnYear10 8.49%
Putnam VT Research Fund | S&P 500 Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 21.83%
5 Years rr_AverageAnnualReturnYear05 15.79%
10 Years rr_AverageAnnualReturnYear10 8.50%
Putnam VT Small Cap Value Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Small Cap Value Fund seeks capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 398%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 398.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in common stocks of small U.S. companies, with a focus on value stocks. Value stocks are issued by companies that we believe are currently undervalued by the market. If we are correct and other investors ultimately recognize the value of the company, the price of its stock may rise. Under normal circumstances, we invest at least 80% of the fund’s net assets in companies of a size similar to those in the Russell 2000 Value Index. This policy may be changed only after 60 days’ notice to shareholders. As of March 31, 2018, the index was composed of companies having market capitalizations of between approximately $7.7 million and $8.5 billion. We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer, industry or sector. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. Value stocks may fail to rebound, and the market may not favor value-style investing. These risks are generally greater for small and midsize companies. From time to time, the fund may invest a significant portion of its assets in companies in one or more related industries or sectors, which would make the fund more vulnerable to adverse developments affecting those industries or sectors.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   −4.02%

Best calendar quarter
Q2 2009  25.25%

Worst calendar quarter
Q4 2008 −28.70%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (4.02%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 25.25%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (28.70%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Putnam VT Small Cap Value Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.62%
Other expenses rr_OtherExpensesOverAssets 0.20%
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.25%
Total annual fund operating expenses rr_ExpensesOverAssets 1.07%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 109
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 340
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 590
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,306
Annual Return 2008 rr_AnnualReturn2008 (39.26%)
Annual Return 2009 rr_AnnualReturn2009 31.84%
Annual Return 2010 rr_AnnualReturn2010 26.30%
Annual Return 2011 rr_AnnualReturn2011 (4.54%)
Annual Return 2012 rr_AnnualReturn2012 17.79%
Annual Return 2013 rr_AnnualReturn2013 39.93%
Annual Return 2014 rr_AnnualReturn2014 3.69%
Annual Return 2015 rr_AnnualReturn2015 (3.90%)
Annual Return 2016 rr_AnnualReturn2016 27.70%
Annual Return 2017 rr_AnnualReturn2017 8.15%
1 Year rr_AverageAnnualReturnYear01 8.15%
5 Years rr_AverageAnnualReturnYear05 14.00%
10 Years rr_AverageAnnualReturnYear10 8.15%
Putnam VT Small Cap Value Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.62%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.20%
Acquired fund fees and expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.25%
Total annual fund operating expenses rr_ExpensesOverAssets 1.32%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 134
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 418
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 723
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,590
1 Year rr_AverageAnnualReturnYear01 7.87%
5 Years rr_AverageAnnualReturnYear05 13.72%
10 Years rr_AverageAnnualReturnYear10 7.89%
Putnam VT Small Cap Value Fund | Russell 2000 Value Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 7.84% [2]
5 Years rr_AverageAnnualReturnYear05 13.01% [2]
10 Years rr_AverageAnnualReturnYear10 8.17% [2]
Putnam VT Sustainable Future Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading *Prior to April 30, 2018, the fund was known as Putnam VT Multi-Cap Value Fund.

Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Sustainable Future Fund seeks long-term capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 61%.

Effective April 30, 2018, the fund’s investment strategy was changed to incorporate sustainability criteria, as described below. Implementing these changes in the fund’s portfolio will result in certain brokerage commission and other transaction costs, which are expected to be incurred largely in May 2018.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 61.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in common stocks of U.S. companies of any size, with a focus on companies whose products and services we believe provide solutions that directly contribute to sustainable social, environmental and economic development (Impact Companies). Stocks of this type of company are typically, but not always, considered to be growth stocks.

Growth stocks are stocks of companies whose earnings are expected to grow faster than those of similar firms, and whose business growth and other characteristics may lead to an increase in stock price. We consider, among other factors, a company’s impact on sustainable environmental, social and economic development (as described below), valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments. We may also invest in non-U.S. companies.

Sustainable investing – Impact Companies. We believe that companies whose products and services produce positive environmental, social and economic development impact also often demonstrate strong financial growth and profitability. Accordingly, in selecting investments, we consider the extent to which a company’s products or services may provide solutions that directly impact sustainable environmental, social and economic development. Environmental impact may include, for example, reduction of carbon emissions and improved water quality. Social impact may include, for example, fair labor practices and responsible supply chain management. Economic development may include, for example, stakeholder analysis and shared value approaches to business practices. It is likely that the metrics and measurements that we use to evaluate environmental, social and economic development impacts will continue to evolve over time.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer, industry or sector. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. Growth stocks may be more susceptible to earnings disappointments, technological obsolescence, falling prices and profits, and the market may not favor growth-style investing. These risks are generally greater for small and midsize companies. From time to time, the fund may invest a significant portion of its assets in companies in one or more related industries or sectors, which would make the fund more vulnerable to adverse developments affecting those industries or sectors. The value of international investments traded in foreign currencies may be adversely impacted by fluctuations in exchange rates. International investments, particularly investments in emerging markets, may carry risks associated with potentially less stable economies or governments (such as the risk of seizure by a foreign government, the imposition of currency or other restrictions, or high levels of inflation or deflation), and may be or become illiquid.

Investing with a focus on Impact Companies may cause the fund to forego otherwise attractive investment opportunities or may increase or decrease the fund’s exposure to certain types of companies and, therefore, to underperform funds that do not invest with a similar focus. In evaluating an investment opportunity, we may make investment decisions based on information and data that is incomplete or inaccurate. In addition, an Impact Company’s products or services may change over time. As a result of these possibilities, the fund may temporarily hold securities that are inconsistent with the fund’s sustainable investment criteria.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. Before April 30, 2018, the fund was managed with a materially different investment strategy and may have achieved materially different performance results under its current investment strategy from that shown for periods before this date. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   −0.63%

Best calendar quarter
Q2 2009  24.85%

Worst calendar quarter
Q4 2008 −26.41%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (0.63%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 24.85%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (26.41%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Performance Table Market Index Changed rr_PerformanceTableMarketIndexChanged

Frank Russell Company is the source and owner of the trademarks, service marks and copyrights related to the Russell Indexes. Russell(R) is a trademark of Frank Russell Company. As of April 30, 2018, the Russell MidCap Growth Index (an unmanaged index representing the smallest 800 companies in the Russell 1000 Index) replaced the Russell 3000 Value Index (an unmanaged index based on the Russell 3000 Index, which measures how U.S. stocks in the equity value index segment perform) as the benchmark for this fund because, in Putnam Investment Management LLC's opinion, the securities tracked by this index more accurately reflect the types of securities that generally will be held by the fund. The average annual total returns of the Russell 3000 Value Index for the one-, five-, and ten-year periods ended on December 31, 2017 were 13.19%, 13.95% and 7.19%, respectively.
Putnam VT Sustainable Future Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.55%
Other expenses rr_OtherExpensesOverAssets 0.23%
Total annual fund operating expenses rr_ExpensesOverAssets 0.78%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 80
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 249
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 433
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 966
Annual Return 2008 rr_AnnualReturn2008 (42.77%)
Annual Return 2009 rr_AnnualReturn2009 39.54%
Annual Return 2010 rr_AnnualReturn2010 24.32%
Annual Return 2011 rr_AnnualReturn2011 (4.87%)
Annual Return 2012 rr_AnnualReturn2012 16.50%
Annual Return 2013 rr_AnnualReturn2013 42.43%
Annual Return 2014 rr_AnnualReturn2014 11.08%
Annual Return 2015 rr_AnnualReturn2015 (4.06%)
Annual Return 2016 rr_AnnualReturn2016 13.23%
Annual Return 2017 rr_AnnualReturn2017 10.94%
1 Year rr_AverageAnnualReturnYear01 10.94%
5 Years rr_AverageAnnualReturnYear05 13.78%
10 Years rr_AverageAnnualReturnYear10 7.69%
Putnam VT Sustainable Future Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.55%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.23%
Total annual fund operating expenses rr_ExpensesOverAssets 1.03%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 105
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 328
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 569
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,259
1 Year rr_AverageAnnualReturnYear01 10.71%
5 Years rr_AverageAnnualReturnYear05 13.50%
10 Years rr_AverageAnnualReturnYear10 7.43%
Putnam VT Sustainable Future Fund | Russell MidCap Growth Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 25.27% [6]
5 Years rr_AverageAnnualReturnYear05 15.30% [6]
10 Years rr_AverageAnnualReturnYear10 9.10% [6]
Putnam VT Sustainable Future Fund | Russell 3000 Value -- Russell MidCap Growth Linked Benchmark (no deduction for fees, expenses or taxes)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 13.19% [7]
5 Years rr_AverageAnnualReturnYear05 13.95% [7]
10 Years rr_AverageAnnualReturnYear10 7.19% [7]
Putnam VT Sustainable Leaders Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading *Prior to April 30, 2018, the fund was known as Putnam VT Multi-Cap Growth Fund

Fund Summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Putnam VT Sustainable Leaders Fund seeks long-term capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. The fees and expenses information does not reflect insurance-related charges or expenses borne by contract holders indirectly investing in the fund. If it did, expenses would be higher.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 71%.

Effective April 30, 2018, the fund’s investment strategy was changed to incorporate sustainability criteria, as described below. Implementing these changes in the fund’s portfolio will result in certain brokerage commission and other transaction costs, which are expected to be incurred largely in May 2018.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 71.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not reflect insurance-related charges or expenses. If it did, expenses would be higher. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Strategy [Heading] rr_StrategyHeading Investments, risks, and performance

Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We invest mainly in common stocks of U.S. companies of any size, with a focus on companies that we believe exhibit a commitment to sustainable business practices. Stocks of companies that exhibit a commitment to sustainable business practices are typically, but not always, considered to be growth stocks. Growth stocks are stocks of companies whose earnings are expected to grow faster than those of similar firms, and whose business growth and other characteristics may lead to an increase in stock price. We consider, among other factors, a company’s sustainable business practices (as described below), valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell investments. We may also invest in non-U.S. companies.

Sustainable investing. We believe that companies that exhibit leadership in sustainable business practice also often exhibit more profitable, durable financial returns with lower risk profiles. Accordingly, in selecting investments, we focus on companies that we believe have a demonstrated commitment to sustainable business practices. This commitment may be reflected through environmental, social and/or corporate governance (ESG) policies, practices or outcomes.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock It is important to understand that you can lose money by investing in the fund.

The value of stocks in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including general financial market conditions, changing market perceptions, changes in government intervention in the financial markets, and factors related to a specific issuer, industry or sector. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. Growth stocks may be more susceptible to earnings disappointments, and the market may not favor growth-style investing. These risks are generally greater for small and midsize companies. From time to time, the fund may invest a significant portion of its assets in companies in one or more related industries or sectors, which would make the fund more vulnerable to adverse developments affecting those industries or sectors. The value of international investments traded in foreign currencies may be adversely impacted by fluctuations in exchange rates. International investments, particularly investments in emerging markets, may carry risks associated with potentially less stable economies or governments (such as the risk of seizure by a foreign government, the imposition of currency or other restrictions, or high levels of inflation or deflation), and may be or become illiquid.

Investing with a focus on companies that exhibit a commitment to sustainable business practices may cause the fund to forego otherwise attractive investment opportunities or may increase or decrease the fund’s exposure to certain types of companies and, therefore, to underperform funds that do not invest with a similar focus. In evaluating an investment opportunity, we may make investment decisions based on information and data that is incomplete or inaccurate. In addition, a company’s business practices may change over time. As a result of these possibilities, the fund may temporarily hold securities that are inconsistent with the fund’s sustainable investment criteria.

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 [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. Before April 30, 2018, the fund was managed with a materially different investment strategy and may have achieved materially different performance results under its current investment strategy from that shown for periods before this date. The performance information does not reflect insurance-related charges or expenses. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class IA shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Year-to-date performance
through 3/31/18   2.84%

Best calendar quarter
Q1 2012  18.06%

Worst calendar quarter
Q4 2008 −22.18%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 2.84%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2012
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.06%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (22.18%)
Performance Table Heading rr_PerformanceTableHeading Average annual total returns
(for periods ending 12/31/17)
Performance Table Market Index Changed rr_PerformanceTableMarketIndexChanged

Frank Russell Company is the source and owner of the trademarks, service marks and copyrights related to the Russell Indexes. Russell(R) is a trademark of Frank Russell Company. As of April 30, 2018, the Russell MidCap Growth Index (an unmanaged index representing the smallest 800 companies in the Russell 1000 Index) replaced the Russell 3000 Value Index (an unmanaged index based on the Russell 3000 Index, which measures how U.S. stocks in the equity value index segment perform) as the benchmark for this fund because, in Putnam Investment Management LLC's opinion, the securities tracked by this index more accurately reflect the types of securities that generally will be held by the fund. The average annual total returns of the Russell 3000 Value Index for the one-, five-, and ten-year periods ended on December 31, 2017 were 13.19%, 13.95% and 7.19%, respectively.
Putnam VT Sustainable Leaders Fund | Class IA  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.55%
Other expenses rr_OtherExpensesOverAssets 0.12%
Total annual fund operating expenses rr_ExpensesOverAssets 0.67%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 68
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 214
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 373
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 835
Annual Return 2008 rr_AnnualReturn2008 (38.62%)
Annual Return 2009 rr_AnnualReturn2009 32.48%
Annual Return 2010 rr_AnnualReturn2010 19.87%
Annual Return 2011 rr_AnnualReturn2011 (4.88%)
Annual Return 2012 rr_AnnualReturn2012 17.09%
Annual Return 2013 rr_AnnualReturn2013 36.74%
Annual Return 2014 rr_AnnualReturn2014 13.80%
Annual Return 2015 rr_AnnualReturn2015 (0.07%)
Annual Return 2016 rr_AnnualReturn2016 8.06%
Annual Return 2017 rr_AnnualReturn2017 29.55%
1 Year rr_AverageAnnualReturnYear01 29.55%
5 Years rr_AverageAnnualReturnYear05 16.84%
10 Years rr_AverageAnnualReturnYear10 8.98%
Putnam VT Sustainable Leaders Fund | Class IB  
Risk Return Abstract rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.55%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.12%
Total annual fund operating expenses rr_ExpensesOverAssets 0.92%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 94
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 293
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 509
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,131
1 Year rr_AverageAnnualReturnYear01 29.22%
5 Years rr_AverageAnnualReturnYear05 16.55%
10 Years rr_AverageAnnualReturnYear10 8.72%
Putnam VT Sustainable Leaders Fund | Russell 3000 Growth Index (no deduction for fees or expenses)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 29.59% [2]
5 Years rr_AverageAnnualReturnYear05 17.16% [2]
10 Years rr_AverageAnnualReturnYear10 9.93% [2]
[1] Reflects Putnam Investment Management, LLC's contractual obligation to limit certain fund expenses through 4/30/19. This obligation may be modified or discontinued only with approval of the fund's Board of Trustees.
[2] Frank Russell Company is the source and owner of the trademarks, service marks and copyrights related to the Russell Indexes. Russell(R) is a trademark of Frank Russell Company.
[3] Restated to reflect current fees.
[4] As of April 30, 2018, the Bloomberg Barclays U.S. MBS Index (an unmanaged index of agency mortgage backed pass-through securities (both fixed-rate and hybrid ARM) guaranteed by Ginnie Mae, Fannie Mae, and Freddie Mac) replaced the Bloomberg Barclays Government Bond Index (an unmanaged index of U.S. Treasury and agency securities) as the benchmark for this fund because, in Putnam Investment Management LLC's opinion, the securities tracked by this index more accurately reflect the types of securities that generally will be held by the fund. The average annual total returns of the Bloomberg Barclays Government Bond Index for the one-, five-, and ten-year periods ended on December 31, 2017 were 2.30%, 1.28% and 3.23%, respectively.
[5] The Bloomberg Barclays Government Bond-Bloomberg Barclays U.S. MBS Linked Benchmark represents performance of the Bloomberg Barclays Government Bond Index from inception date of the fund, February 1, 2000, through April 29, 2018 and performance of the Bloomberg Barclays U.S. MBS Index from April 30, 2018 through the current period.
[6] Frank Russell Company is the source and owner of the trademarks, service marks and copyrights related to the Russell Indexes. Russell(R) is a trademark of Frank Russell Company. As of April 30, 2018, the Russell MidCap Growth Index (an unmanaged index representing the smallest 800 companies in the Russell 1000 Index) replaced the Russell 3000 Value Index (an unmanaged index based on the Russell 3000 Index, which measures how U.S. stocks in the equity value index segment perform) as the benchmark for this fund because, in Putnam Investment Management LLC's opinion, the securities tracked by this index more accurately reflect the types of securities that generally will be held by the fund. The average annual total returns of the Russell 3000 Value Index for the one-, five-, and ten-year periods ended on December 31, 2017 were 13.19%, 13.95% and 7.19%, respectively.
[7] The Russell 3000 Value -- Russell Midcap Growth Linked Benchmark represents performance of the Russell 3000 Value Index from the inception date of the fund, May 1, 2003, through April 30, 2018 and performance of the Russell MidCap Growth Index from May 1, 2018 through the current period.