v3.25.2
Shareholder Report
 6 Months Ended
Jun. 30, 2025
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, 2025
Class IA  
Shareholder Report [Line Items]  
Fund Name Putnam VT Small Cap Growth Fund
Class Name Class IA
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Putnam VT Small Cap Growth Fund for the period January 1, 2025, to June 30, 2025.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) 225-1581.
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
$44
0.87%
[1],[2]
Expenses Paid, Amount $ 44 [1]
Expense Ratio, Percent 0.87% [1]
Net Assets $ 35,318,247
Holdings Count | $ / shares 101 [3]
Investment Company Portfolio Turnover 30.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of June 30, 2025)
Total Net Assets
$35,318,247
Total Number of Portfolio Holdings*
101
Portfolio Turnover Rate
30%
[3]
Holdings [Text Block]
image
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class IB  
Shareholder Report [Line Items]  
Fund Name Putnam VT Small Cap Growth Fund
Class Name Class IB
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Putnam VT Small Cap Growth Fund for the period January 1, 2025, to June 30, 2025.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) 225-1581.
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
$57
1.12%
[4],[5]
Expenses Paid, Amount $ 57 [4]
Expense Ratio, Percent 1.12% [4]
Net Assets $ 35,318,247
Holdings Count | $ / shares 101 [6]
Investment Company Portfolio Turnover 30.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of June 30, 2025)
Total Net Assets
$35,318,247
Total Number of Portfolio Holdings*
101
Portfolio Turnover Rate
30%
[6]
Holdings [Text Block]
image
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]
† Annualized.
[3]
* Does not include derivatives, except purchased options, if any.  
[4]
1 Does not reflect expenses incurred from investing through variable annuity or variable life insurance products.
[5]
† Annualized.
[6]
* Does not include derivatives, except purchased options, if any.