Label	Element	Value
Risk Return Abstract	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	JOHN HANCOCK VARIABLE INSURANCE TRUST
Prospectus Date	rr_ProspectusDate	Apr. 28, 2025
International Small Company Trust
Risk Return Abstract	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	<span style="color:#000000;font-family:Arial Narrow;font-size:24pt;">International Small Company Trust</span>
Objective [Heading]	rr_ObjectiveHeading	<span style="color:#000000;font-family:Arial Narrow;font-size:10pt;font-weight:bold;">Investment objective</span>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	To seek long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	<span style="color:#000000;font-family:Arial Narrow;font-size:10pt;font-weight:bold;">Fees and expenses</span>
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy, hold, and sell shares of the fund. The fees and expenses do not reflect fees and expenses of any variable insurance or variable annuities contract that may use the fund as its underlying investment option and would be higher if they did.
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	<span style="font-family:Arial Narrow;font-size:8pt;font-weight:bold;margin-left:0.0pt;">Annual fund operating expenses (%) </span><span style="font-family:Arial Narrow;font-size:8pt;margin-left:0.0pt;">(expenses that you pay each year as a percentage of the value of your investment)</span>
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	<span style="color:#000000;font-family:Arial Narrow;font-size:10pt;font-weight:bold;">Portfolio turnover</span>
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund’s performance. During its most recent fiscal year, the fund’s portfolio turnover rate was 13% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	13.00%
Expense Example [Heading]	rr_ExpenseExampleHeading	<span style="color:#000000;font-family:Arial Narrow;font-size:10pt;font-weight:bold;">Expense example</span>
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The examples are intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The examples assume that $10,000 is invested in the fund for the periods indicated and then all shares are redeemed at the end of those periods. The examples also assume that the investment has a 5% return each year and that the fund’s operating expenses remain the same. The expense example does not reflect fees and expenses of any variable insurance contract that may use the fund as its underlying investment option and would be higher if they did. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	<span style="color:#000000;font-family:Arial Narrow;font-size:10pt;font-weight:bold;">Principal investment strategies</span>
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal market conditions, the fund invests at least 80% of its net assets (plus any borrowings for investment purposes) in securities of small cap companies in the particular markets in which the fund invests. (The fund will provide written notice to shareholders at least 60 days prior to a change in its 80% investment policy.) Based on market capitalization data as of February 28, 2025, the market capitalization of a small company in any country in which the fund invests would generally be below $9.3 billion. This threshold will vary by country or region. The fund will primarily invest in a broad and diverse group of equity securities of foreign small companies of developed markets, but may also hold equity securities of companies located in emerging markets. The fund invests its assets in securities listed on bona fide securities exchanges. These exchanges may be either within or outside the issuer’s domicile country. The securities may be listed or traded in the form of American Depositary Receipts (ADRs), European Depositary Receipts (EDRs), Global Depositary Receipts (GDRs), Non-Voting Depositary Receipts (NVDRs) or other similar securities, including dual-listed securities. The subadvisor determines company size on a country or region specific basis and based primarily on market capitalization. In the countries or regions authorized for investment, the subadvisor first ranks eligible companies listed on selected exchanges based on the companies’ market capitalizations. The subadvisor then determines the universe of eligible stocks by defining the maximum market capitalization of a small company that may be purchased by the fund with respect to each country or region. This threshold will vary by country or region, and dollar amounts will change due to market conditions. The fund intends to purchase securities in each applicable country using a market capitalization weighted approach. The subadvisor, using this approach and its judgment, will seek to set country weights based on the relative market capitalizations of eligible small companies within each country. See “Market Capitalization Weighted Approach” below. The weightings of countries in the fund may vary from their weightings in international indices, such as those published by FTSE Russell or MSCI. The fund also may use derivatives such as futures contracts and options on futures contracts, to increase or decrease equity market exposure  based on actual or expected cash inflows to or outflows from the fund. The fund may enter into futures contracts and options on futures contracts for foreign or U.S. equity securities and indices. The fund may also enter into forward currency contracts to facilitate the settlement of equity purchases of foreign securities, repatriation of foreign currency balances or exchange of one foreign currency for another currency. In addition to money market instruments and other short-term investments, the fund may invest in affiliated and unaffiliated unregistered money market funds to manage the fund’s cash pending investment in other securities or to maintain liquidity for the payment of redemptions or other purposes. Investments in money market funds may involve a duplication of certain fees and expenses. Generally, the fund does not seek current income as an investment objective and investments will not be based upon an issuer’s dividend payment policy or record. However, many of the companies whose securities will be included in the fund do pay dividends. It is anticipated, therefore, that the fund will receive dividend income. The subadvisor will determine in its discretion when and whether to invest in countries that have been authorized for investment by its Investment Committee, depending on a number of factors such as asset growth in the fund, constraints imposed within a country’s market, and characteristics of each country’s market. The subadvisor’s Investment Committee may authorize other countries for investment in the future and the fund may continue to hold investments in countries not currently authorized for investment but that had previously been authorized for investment. Market Capitalization Weighted Approach The fund structure involves market capitalization weighting in determining individual security weights and, where applicable, country or region weights. Market capitalization weighting means each security is generally purchased based on the issuer’s relative market capitalization. Market capitalization weighting may be modified by the subadvisor for a variety of reasons. The subadvisor may adjust the representation in the fund of an eligible company, or exclude a company, after  considering such factors as free float, price momentum, short-run reversals, trading strategies, liquidity, size, relative price, profitability,  investment characteristics, and other factors the subadvisor determines to be appropriate. An equity issuer is considered to have a low relative price (i.e., a value stock) primarily because it has a low price in relation to its book value. In assessing relative price, the subadvisor may consider additional factors such as price to cash flow or price to earnings ratios. In assessing  profitability, the subadvisor considers different ratios, such as that of earnings or profits from operations relative to book value or assets. In assessing a company’s investment characteristics, the subadvisor considers ratios such as recent changes in assets divided by total assets. The criteria the subadvisor uses for assessing relative price, profitability and investment characteristics are subject to change from time to time. The subadvisor may deviate from market capitalization weighting to limit or fix the exposure of the fund to a particular country or issuer to a maximum proportion of the assets of the fund. The subadvisor may exclude the stock of a company that meets applicable market capitalization criteria if the subadvisor determines, in its judgment, that the purchase of such stock is inappropriate in light of other conditions. The subadvisor may decrease the allocation of the fund’s assets to eligible small capitalization companies that generally have lower profitability and/or higher relative prices. These adjustments will result in a deviation from traditional market capitalization weighting. Country weights may be based on the total market capitalization of companies within each country. The calculation of country weights may take into consideration the free float of companies within a country or whether these companies are eligible to be purchased for the particular strategy. In addition, to maintain a satisfactory level of diversification, the Investment Committee may limit or fix the exposure to a particular country or region to a maximum proportion of the assets of that vehicle. Country weights may also vary due to general day-to-day trading patterns and price movements. The weighting of countries may vary from their weighting in published international indices.
Risk [Heading]	rr_RiskHeading	<span style="color:#000000;font-family:Arial Narrow;font-size:10pt;font-weight:bold;">Principal risks</span>
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	<span style="color:#000000;font-family:Arial Narrow;font-size:10pt;font-weight:bold;">Past performance</span>
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following information illustrates the variability of the fund’s returns and provides some indication of the risks of investing in the fund by showing changes in the fund’s performance from year to year and by showing how the fund’s average annual returns compared with a broad-based securities market index.Past performance does not indicate future results. The MSCI World ex USA Small Cap Index shows how the fund’s performance compares against the returns of similar investments. All figures assume dividend reinvestment. The performance information below does not reflect fees and expenses of any variable insurance contract which may use JHVIT as its underlying investment option. If such fees and expenses had been reflected, performance would be lower.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	<span style="font-family:Arial Narrow;font-size:9pt;">The following information illustrates the variability of the fund’s returns and provides some indication of the risks of investing in the fund by showing changes in the fund’s performance from year to year and by showing how the fund’s average annual returns compared with a broad-based securities market index.</span>
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	<span style="font-family:Arial Narrow;font-size:9pt;">Past performance does not indicate future results.</span>
Bar Chart [Heading]	rr_BarChartHeading	<span style="font-family:Arial Narrow;font-size:9pt;font-weight:bold;">Calendar year total returns (%)—Series NAV</span>
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best quarter:Q2 202020.80%Worst quarter:Q1 2020-30.16%
Performance Table Heading	rr_PerformanceTableHeading	<span style="font-family:Arial Narrow;font-size:8pt;font-weight:bold;margin-left:0.0pt;">Average annual total returns (%)—as of 12/31/2024</span>
Performance Table Market Index Changed	rr_PerformanceTableMarketIndexChanged	<span style="font-family:Arial Narrow;font-size:8pt;">The fund has designated the MSCI World ex-USA Index as its new broad-based securities market index in accordance with the revised definition for such an index.</span>
International Small Company Trust | Risk Lose Money [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Many factors affect performance, and fund shares will fluctuate in price, meaning you could lose money.
International Small Company Trust | Risk Not Insured Depository Institution [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
International Small Company Trust | Cash And Cash Equivalents Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Cash and cash equivalents risk.  Under certain market conditions, such as during a rising stock market, rising interest rate or rising credit spread markets, the use of cash and/or cash equivalents, including money market instruments, could have a negative effect on the fund’s ability to achieve its investment objective and may negatively impact the fund’s performance.
International Small Company Trust | Credit And Counterparty Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Credit and counterparty risk.  The counterparty to an over-the-counter derivatives contract or a borrower of fund securities may not make timely payments or otherwise honor its obligations.
International Small Company Trust | Currency Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Currency risk.  Fluctuations in exchange rates may adversely affect the U.S. dollar value of a fund’s investments. Foreign currencies may decline in value, which could negatively impact performance.
International Small Company Trust | Economic And Market Events Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Economic and market events risk.  Events in the U.S. and global financial markets, including actions taken by the U.S. Federal Reserve or foreign central banks to stimulate or stabilize economic growth, may at times result in unusually high market volatility, which could negatively impact performance. Reduced liquidity in credit and fixed-income markets could adversely affect issuers worldwide. Banks and financial services companies could suffer losses if interest rates rise or economic conditions deteriorate.
International Small Company Trust | Equity Securities Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Equity securities risk.  The price of equity securities may decline due to changes in a company’s financial condition or overall market conditions. Securities the manager believes are undervalued may never realize their full potential value, and in certain markets value stocks may underperform the market as a whole.
International Small Company Trust | Foreign Securities Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Foreign securities risk.  Less information may be publicly available regarding foreign issuers, including foreign government issuers. Foreign securities may be subject to foreign taxes and may be more volatile than U.S. securities. Currency fluctuations and political and economic developments may adversely impact the value of foreign securities. The risks of investing in foreign securities are magnified in emerging markets. Depositary receipts are subject to most of the risks associated with investing in foreign securities directly because the value of a depositary receipt is dependent upon the market price of the underlying foreign equity security. Depositary receipts are also subject to liquidity risk.
International Small Company Trust | Geographic Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Geographic risk.  A natural or other disaster could occur in a geographic region in which the fund invests, which could affect the economy or particular business operations of companies in the specific geographic region, causing an adverse impact on the fund’s investments in the affected region.
International Small Company Trust | Hedging Derivatives And Other Strategic Transactions Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Hedging, derivatives, and other strategic transactions risk.  Hedging, derivatives, and other strategic transactions may increase a fund’s volatility and could produce disproportionate losses, potentially more than the fund’s principal investment. Risks of these transactions are different from and possibly greater than risks of investing directly in securities and other traditional instruments. Under certain market conditions, derivatives could become harder to value or sell and may become subject to liquidity risk (i.e., the inability to enter into closing transactions). Derivatives and other strategic transactions that the fund intends to utilize include: foreign currency forward contracts, futures contracts, options on futures contracts, and options. Foreign currency forward contracts, futures contracts, and options generally are subject to counterparty risk. Derivatives associated with foreign currency transactions are subject to currency risk.
International Small Company Trust | Industrials Sector Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Industrials sector risk.  Companies in the industrials sector may be affected by general economic conditions, commodity production and pricing, supply and demand fluctuations, environmental and other government regulations, geopolitical events, interest rates, insurance costs, technological developments, liabilities arising from governmental or civil actions, labor relations, input controls, and government spending.
International Small Company Trust | Investment Company Securities Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Investment company securities risk.  Fund shareholders indirectly bear their proportionate share of the expenses of any investment company in which the fund invests. The total return on such investments will be reduced by the operating expenses and fees of such other investment companies, including advisory fees.
International Small Company Trust | Liquidity Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Liquidity risk.  The extent (if at all) to which a security may be sold or a derivative position closed without negatively impacting its market value may be impaired by reduced market activity or participation, legal restrictions, or other economic and market impediments.
International Small Company Trust | Operational And Cybersecurity Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Operational and cybersecurity risk.  Cybersecurity breaches may allow an unauthorized party to gain access to fund assets, customer data, or proprietary information, or cause a fund or its service providers to suffer data corruption or lose operational functionality. Similar incidents affecting issuers of a fund’s securities may negatively impact performance. Operational risk may arise from human error, error by third parties, communication errors, or technology failures, among other causes.
International Small Company Trust | Quantitative Modeling Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Quantitative modeling risk.  Quantitative models may not accurately predict future market movements or characteristics, which may negatively impact performance. Models also may perform differently than expected due to implementation problems, technological malfunction, or programming or data inaccuracies, among other possible issues.
International Small Company Trust | Sector Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Sector risk.  When a fund focuses its investments in certain sectors of the economy, its performance may be driven largely by sector performance and could fluctuate more widely than if the fund were invested more evenly across sectors.
International Small Company Trust | Small And Mid Sized Company Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Small and mid-sized company risk.  Small and mid-sized companies are generally less established and may be more volatile than larger companies. Small and/or mid-capitalization securities may underperform the market as a whole.
International Small Company Trust | Series I
Risk Return Abstract	rr_RiskReturnAbstract
Management fee	rr_ManagementFeesOverAssets	0.80%
Distribution and service (Rule 12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.05%
Other expenses	rr_OtherExpensesOverAssets	0.21%
Total annual fund operating expenses	rr_ExpensesOverAssets	1.06%
1 year	rr_ExpenseExampleYear01	$ 108
3 years	rr_ExpenseExampleYear03	337
5 years	rr_ExpenseExampleYear05	585
10 years	rr_ExpenseExampleYear10	$ 1,294
1 year	rr_AverageAnnualReturnYear01	3.07%
5 year	rr_AverageAnnualReturnYear05	3.35%
10 year	rr_AverageAnnualReturnYear10	5.27%
International Small Company Trust | Series II
Risk Return Abstract	rr_RiskReturnAbstract
Management fee	rr_ManagementFeesOverAssets	0.80%
Distribution and service (Rule 12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.21%
Total annual fund operating expenses	rr_ExpensesOverAssets	1.26%
1 year	rr_ExpenseExampleYear01	$ 128
3 years	rr_ExpenseExampleYear03	400
5 years	rr_ExpenseExampleYear05	692
10 years	rr_ExpenseExampleYear10	$ 1,523
1 year	rr_AverageAnnualReturnYear01	2.82%
5 year	rr_AverageAnnualReturnYear05	3.15%
10 year	rr_AverageAnnualReturnYear10	5.07%
International Small Company Trust | NAV
Risk Return Abstract	rr_RiskReturnAbstract
Management fee	rr_ManagementFeesOverAssets	0.80%
Distribution and service (Rule 12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.21%
Total annual fund operating expenses	rr_ExpensesOverAssets	1.01%
1 year	rr_ExpenseExampleYear01	$ 103
3 years	rr_ExpenseExampleYear03	322
5 years	rr_ExpenseExampleYear05	558
10 years	rr_ExpenseExampleYear10	$ 1,236
2015	rr_AnnualReturn2015	6.68%
2016	rr_AnnualReturn2016	4.95%
2017	rr_AnnualReturn2017	29.60%
2018	rr_AnnualReturn2018	(20.08%)
2019	rr_AnnualReturn2019	22.70%
2020	rr_AnnualReturn2020	8.41%
2021	rr_AnnualReturn2021	13.77%
2022	rr_AnnualReturn2022	(18.17%)
2023	rr_AnnualReturn2023	13.59%
2024	rr_AnnualReturn2024	3.11%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	<span style="color:#000000;font-family:Arial Narrow;font-size:8pt;font-weight:bold;margin-left:0.0pt;">Best quarter:</span>
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2020
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	20.80%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	<span style="color:#000000;font-family:Arial Narrow;font-size:8pt;font-weight:bold;margin-left:0.0pt;">Worst quarter:</span>
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Mar. 31, 2020
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(30.16%)
1 year	rr_AverageAnnualReturnYear01	3.11%
5 year	rr_AverageAnnualReturnYear05	3.40%
10 year	rr_AverageAnnualReturnYear10	5.34%
International Small Company Trust | MSCI World ex-USA Index (reflects no deduction for fees, expenses, or taxes, except foreign withholding taxes on dividends)
Risk Return Abstract	rr_RiskReturnAbstract
1 year	rr_AverageAnnualReturnYear01	4.70%	[1]
5 year	rr_AverageAnnualReturnYear05	5.10%	[1]
10 year	rr_AverageAnnualReturnYear10	5.26%	[1]
International Small Company Trust | MSCI World ex USA Small Cap Index (reflects no deduction for fees, expenses, or taxes, except foreign withholding taxes on dividends)
Risk Return Abstract	rr_RiskReturnAbstract
1 year	rr_AverageAnnualReturnYear01	2.76%
5 year	rr_AverageAnnualReturnYear05	2.87%
10 year	rr_AverageAnnualReturnYear10	5.49%

[1] The fund has designated the MSCI World ex-USA Index as its new broad-based securities market index in accordance with the revised definition for such an index.