v3.26.1
Shareholder Report
 6 Months Ended
Jun. 30, 2026
USD ($)
$ / shares
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name Putnam Variable Trust
Entity Central Index Key 0000822671
Entity Investment Company Type N-1A
Document Period End Date Jun. 30, 2026
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Class IA  
Shareholder Report [Line Items]  
Fund Name Putnam VT Diversified Income Fund
Class Name Class IA
No Trading Symbol true
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Putnam VT Diversified Income Fund for the period January 1, 2026, to June 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) 225-1581.
Additional Information Phone Number (800) 225-1581
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS? (based on a hypothetical $10,000 investment)
Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment*,†
Class IA1
$39
0.78%
[1],[2],[3]
Expenses Paid, Amount $ 39 [1]
Expense Ratio, Percent 0.78% [1]
Net Assets $ 94,513,288
Holdings Count | $ / shares 640
Investment Company Portfolio Turnover 242.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of June 30, 2026)
Total Net Assets
$94,513,288
Total Number of Portfolio Holdings (excludes derivatives, except purchased options, if any)
640
Portfolio Turnover Rate
242%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of June 30, 2026)
Portfolio Composition* (% of Total Investments)
image
 [4]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class IB  
Shareholder Report [Line Items]  
Fund Name Putnam VT Diversified Income Fund
Class Name Class IB
No Trading Symbol true
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Putnam VT Diversified Income Fund for the period January 1, 2026, to June 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) 225-1581.
Additional Information Phone Number (800) 225-1581
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS? (based on a hypothetical $10,000 investment)
Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment*,†
Class IB1
$51
1.03%
[5],[6],[7]
Expenses Paid, Amount $ 51 [5]
Expense Ratio, Percent 1.03% [5]
Net Assets $ 94,513,288
Holdings Count | $ / shares 640
Investment Company Portfolio Turnover 242.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of June 30, 2026)
Total Net Assets
$94,513,288
Total Number of Portfolio Holdings (excludes derivatives, except purchased options, if any)
640
Portfolio Turnover Rate
242%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of June 30, 2026)
Portfolio Composition* (% of Total Investments)
image
 [8]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
[1]
1 Does not reflect expenses incurred from investing through variable annuity or variable life insurance products.
[2]
* Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher.
[3]
† Annualized.
[4]
* Does not include derivatives, except purchased options, if any.  
[5]
1 Does not reflect expenses incurred from investing through variable annuity or variable life insurance products.
[6]
* Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher.
[7]
† Annualized.
[8]
* Does not include derivatives, except purchased options, if any.