<?xml version="1.0" encoding="utf-8"?>
<xbrl
  xmlns="http://www.xbrl.org/2003/instance"
  xmlns:dei="http://xbrl.sec.gov/dei/2026"
  xmlns:fnd="http://xbrl.sec.gov/fnd/2026q3"
  xmlns:link="http://www.xbrl.org/2003/linkbase"
  xmlns:xlink="http://www.w3.org/1999/xlink">
    <link:schemaRef xlink:href="ft13251-20261009.xsd" xlink:type="simple"/>
    <context id="AsOf2026-10-09">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0002144038</identifier>
        </entity>
        <period>
            <startDate>2026-10-09</startDate>
            <endDate>2026-10-09</endDate>
        </period>
    </context>
    <dei:AmendmentFlag contextRef="AsOf2026-10-09" id="Fact000003">false</dei:AmendmentFlag>
    <dei:EntityCentralIndexKey contextRef="AsOf2026-10-09" id="Fact000004">0002144038</dei:EntityCentralIndexKey>
    <dei:DocumentType contextRef="AsOf2026-10-09" id="Fact000010">S-6</dei:DocumentType>
    <dei:EntityRegistrantName contextRef="AsOf2026-10-09" id="Fact000011">FT 13251</dei:EntityRegistrantName>
    <dei:DocumentPeriodEndDate contextRef="AsOf2026-10-09" id="Fact000012">2026-10-09</dei:DocumentPeriodEndDate>
    <fnd:NmRule35d1TermDfnTextBlock contextRef="AsOf2026-10-09" id="Fact000013">

&lt;p style="font: bold 11pt/12pt Times New Roman, Times, Serif; margin: 2pt 0"&gt;Objective.&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 0; text-indent: 0.25in"&gt;The Trust seeks above-average total return by
investing in a portfolio of common stocks diversified across various market capitalizations, growth and value styles, sectors and countries.
&lt;span style="letter-spacing: -0.05pt"&gt;Under normal circumstances, the Trust will invest at least 80% of its assets in&#160;equity securities.&lt;/span&gt;&lt;/p&gt;

</fnd:NmRule35d1TermDfnTextBlock>
    <fnd:NmRule35d1TermSlctnCritTextBlock contextRef="AsOf2026-10-09" id="Fact000014">

&lt;p style="font: bold 11pt/11pt Times New Roman, Times, Serif; margin: 2pt 0"&gt;Portfolio Selection Process.&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 4pt 0 2pt; text-indent: 0.25in"&gt;&lt;i&gt;1. Identify the universe of eligible
stocks&lt;/i&gt;.&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0; text-indent: 0.25in"&gt;The Diversified Equity Strategic Allocation
Portfolio applies a model which analyzes domestic and international stocks to assess valuations based on risk, value, and growth factors.
Growth stocks are stocks with higher than average price to book ratios, which are considered by the Sponsor to have the potential to outperform
the overall market over time because of their future potential. Value stocks are stocks with lower than average price to book ratios,
which are considered by the Sponsor to be currently trading below their intrinsic value and are therefore likely to provide a superior
return.&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0; text-indent: 0.25in"&gt;The first step in our selection process is
to establish a universe of stocks as of two business days prior to the Initial Date of Deposit (the &#x201c;selection date&#x201d;) from
which the portfolio will be selected. The universe is divided into seven distinct styles consisting of six domestic equity asset classes
and one international equity asset class.&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0; text-indent: 0.25in"&gt;The domestic universe is established by identifying
the 3,000 largest U.S. stocks (excluding limited partnerships, royalty trusts, regulated investment companies and business development
companies) and then separating them into large-cap (largest 10%), mid-cap (next 20%), and small-cap (remaining 70%). The stocks in each
group are then divided evenly between growth and value by their price to book ratios to establish the universe of stocks eligible for
selection from within each market capitalization range. In the case of the small-cap universe, only the 250 largest stocks with a minimum
average daily trading volume of $1,000,000 within each growth and value group are included to ensure sufficient liquidity. The international
universe consists of the 100 largest companies from developed nations whose shares are either directly listed on a U.S. securities exchange
or are in the form of American Depositary Receipts/ADRs which trade on the over-the-counter market or are listed on a U.S. securities
exchange. Regardless of universe, stocks with a price of $1,000 or higher per share are not eligible for selection.&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 4pt 0 2pt; text-indent: 0.25in"&gt;Number of Eligible Stocks in Each Selection
Universe:&lt;/p&gt;

&lt;table cellpadding="0" cellspacing="0" style="font: 12pt Times New Roman, Times, Serif; border-collapse: collapse; width: 100%"&gt;
  &lt;tr style="vertical-align: top"&gt;
    &lt;td style="border: black 1pt solid; width: 15%; line-height: 11pt"&gt;&#160;&lt;/td&gt;
    &lt;td style="border-top: black 1pt solid; border-right: black 1pt solid; border-bottom: black 1pt solid; width: 17%; padding-top: 1pt; line-height: 11pt; text-align: center"&gt;&lt;span style="font-size: 9pt"&gt;&lt;b&gt;Domestic&lt;br/&gt;
Large-Cap&lt;/b&gt;&lt;/span&gt;&lt;/td&gt;
    &lt;td style="border-top: black 1pt solid; border-right: black 1pt solid; border-bottom: black 1pt solid; width: 17%; padding-top: 1pt; line-height: 11pt; text-align: center"&gt;&lt;span style="font-size: 9pt"&gt;&lt;b&gt;Domestic&lt;br/&gt;
Mid-Cap&lt;/b&gt;&lt;/span&gt;&lt;/td&gt;
    &lt;td style="border-top: black 1pt solid; border-right: black 1pt solid; border-bottom: black 1pt solid; width: 17%; padding-top: 1pt; line-height: 11pt; text-align: center"&gt;&lt;span style="font-size: 9pt"&gt;&lt;b&gt;Domestic&lt;br/&gt;
Small-Cap&lt;/b&gt;&lt;/span&gt;&lt;/td&gt;
    &lt;td style="border-top: black 1pt solid; border-right: black 1pt solid; border-bottom: black 1pt solid; width: 34%; padding-top: 1pt; line-height: 11pt; text-align: center"&gt;&lt;span style="font-size: 9pt"&gt;&lt;b&gt;&lt;br/&gt;
International&lt;/b&gt;&lt;/span&gt;&lt;/td&gt;&lt;/tr&gt;
  &lt;tr&gt;
    &lt;td style="border-right: black 1pt solid; border-bottom: black 1pt solid; border-left: black 1pt solid; padding-left: 2pt; line-height: 11pt"&gt;&lt;span style="font-size: 9pt"&gt;Growth&lt;/span&gt;&lt;/td&gt;
    &lt;td style="border-right: black 1pt solid; border-bottom: black 1pt solid; line-height: 11pt; text-align: center"&gt;&lt;span style="font-size: 9pt"&gt;150&lt;/span&gt;&lt;/td&gt;
    &lt;td style="border-right: black 1pt solid; border-bottom: black 1pt solid; line-height: 11pt; text-align: center"&gt;&lt;span style="font-size: 9pt"&gt;300&lt;/span&gt;&lt;/td&gt;
    &lt;td style="border-right: black 1pt solid; border-bottom: black 1pt solid; line-height: 11pt; text-align: center"&gt;&lt;span style="font-size: 9pt"&gt;250&lt;/span&gt;&lt;/td&gt;
    &lt;td rowspan="2" style="border-right: black 1pt solid; border-bottom: black 1pt solid; text-indent: 0in; line-height: 11pt; font-size: 8pt; text-align: center"&gt;&lt;span style="font-size: 9pt"&gt;100&lt;/span&gt;&lt;/td&gt;&lt;/tr&gt;
  &lt;tr&gt;
    &lt;td style="border-right: black 1pt solid; border-bottom: black 1pt solid; border-left: black 1pt solid; padding-left: 2pt; line-height: 11pt"&gt;&lt;span style="font-size: 9pt"&gt;Value&lt;/span&gt;&lt;/td&gt;
    &lt;td style="border-right: black 1pt solid; border-bottom: black 1pt solid; line-height: 11pt; text-align: center"&gt;&lt;span style="font-size: 9pt"&gt;150&lt;/span&gt;&lt;/td&gt;
    &lt;td style="border-right: black 1pt solid; border-bottom: black 1pt solid; line-height: 11pt; text-align: center"&gt;&lt;span style="font-size: 9pt"&gt;300&lt;/span&gt;&lt;/td&gt;
    &lt;td style="border-right: black 1pt solid; border-bottom: black 1pt solid; line-height: 11pt; text-align: center"&gt;&lt;span style="font-size: 9pt"&gt;250&lt;/span&gt;&lt;/td&gt;&lt;/tr&gt;
  &lt;/table&gt;
&lt;p style="font: bold 2pt/11pt Arial, Helvetica, Sans-Serif; margin: 0"&gt;&#160;&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 4pt 0 2pt; text-indent: 0.25in"&gt;&lt;i&gt;2. Apply the rules-based stock selection
models&lt;/i&gt;.&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0; text-indent: 0.25in"&gt;We then rank the stocks within each of the
seven universes based on two multi-factor models, with each factor within a model receiving an equal weight. Half of a stock&#x2019;s ranking
is based on a risk model and applies to all seven universes. The remaining half of a stock&#x2019;s ranking is based on a model which is
determined by the stock&#x2019;s style designation (i.e., growth, value or international). Value and international stocks are ranked together
on one model, while growth stocks are ranked using a separate model.&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 4pt 0 1pt"&gt;&lt;span style="font-weight: normal"&gt;&lt;i&gt;Stock Selection Factors.&lt;/i&gt;&lt;/span&gt;&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0 0 0.25in"&gt;Risk Model. The following factors are used to evaluate
and rank the stocks within the model:&lt;/p&gt;

&lt;table cellpadding="0" cellspacing="0" style="font: 10pt/11pt Times New Roman, Times, Serif; margin-top: 0; margin-bottom: 0; width: 100%"&gt;
  &lt;tr style="vertical-align: top"&gt;
    &lt;td style="width: 0.25in"&gt;&#160;&lt;/td&gt;
    &lt;td style="width: 0.25in"&gt;&#x2022;&lt;/td&gt;
    &lt;td&gt;Debt to equity ratio. Compares a company&#x2019;s long-term debt to its stockholder&#x2019;s equity. Companies that have a lower debt to equity ratio are assigned a higher ranking.&lt;/td&gt;&lt;/tr&gt;
  &lt;/table&gt;
&lt;table cellpadding="0" cellspacing="0" style="font: 10pt/11pt Times New Roman, Times, Serif; margin-top: 0; margin-bottom: 0; width: 100%"&gt;
  &lt;tr style="vertical-align: top"&gt;
    &lt;td style="width: 0.25in"&gt;&#160;&lt;/td&gt;
    &lt;td style="width: 0.25in"&gt;&#x2022;&lt;/td&gt;
    &lt;td&gt;Beta. Compares a security&#x2019;s volatility relative to the market. A security with a beta less than 1.0 would generally be considered lower risk than the market. Companies that have a lower beta are assigned a higher ranking.&lt;/td&gt;&lt;/tr&gt;
  &lt;/table&gt;
&lt;table cellpadding="0" cellspacing="0" style="font: 10pt/11pt Times New Roman, Times, Serif; margin-top: 0; margin-bottom: 0; width: 100%"&gt;
  &lt;tr style="vertical-align: top"&gt;
    &lt;td style="width: 0.25in"&gt;&#160;&lt;/td&gt;
    &lt;td style="width: 0.25in"&gt;&#x2022;&lt;/td&gt;
    &lt;td&gt;Earnings variability. Compares a company&#x2019;s trailing 12-months earnings per share from the previous five years against a linear trend line. Companies that have more consistent earnings growth are assigned a higher ranking.&lt;/td&gt;&lt;/tr&gt;
  &lt;/table&gt;
&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0 0 0.25in"&gt;Value &amp;amp; International Model. The following factors
are used to evaluate and rank the stocks within the model:&lt;/p&gt;

&lt;table cellpadding="0" cellspacing="0" style="font: 10pt/11pt Times New Roman, Times, Serif; margin-top: 0; margin-bottom: 0; width: 100%"&gt;
  &lt;tr style="vertical-align: top"&gt;
    &lt;td style="width: 0.25in"&gt;&#160;&lt;/td&gt;
    &lt;td style="width: 0.25in"&gt;&#x2022;&lt;/td&gt;
    &lt;td&gt;Price to book ratio. Compares a company&#x2019;s market capitalization to its book value. Companies that have a lower, but positive, price to book ratio are assigned a higher ranking.&lt;/td&gt;&lt;/tr&gt;
  &lt;/table&gt;
&lt;table cellpadding="0" cellspacing="0" style="font: 10pt/11pt Times New Roman, Times, Serif; margin-top: 0; margin-bottom: 0; width: 100%"&gt;
  &lt;tr style="vertical-align: top"&gt;
    &lt;td style="width: 0.25in"&gt;&#160;&lt;/td&gt;
    &lt;td style="width: 0.25in"&gt;&#x2022;&lt;/td&gt;
    &lt;td&gt;Price to cash flow ratio. Compares a company&#x2019;s market capitalization to its cash flow generated. Companies that have a lower, but positive, price to cash flow ratio are assigned a higher ranking.&lt;/td&gt;&lt;/tr&gt;
  &lt;/table&gt;
&lt;table cellpadding="0" cellspacing="0" style="font: 10pt/11pt Times New Roman, Times, Serif; margin-top: 0; margin-bottom: 0; width: 100%"&gt;
  &lt;tr style="vertical-align: top"&gt;
    &lt;td style="width: 0.25in"&gt;&#160;&lt;/td&gt;
    &lt;td style="width: 0.25in"&gt;&#x2022;&lt;/td&gt;
    &lt;td&gt;Return on assets. Compares a company&#x2019;s trailing 12-months net income to its total assets. Companies that have higher return on assets are assigned a higher ranking.&lt;/td&gt;&lt;/tr&gt;
  &lt;/table&gt;
&lt;table cellpadding="0" cellspacing="0" style="font: 10pt/11pt Times New Roman, Times, Serif; margin-top: 0; margin-bottom: 0; width: 100%"&gt;
  &lt;tr style="vertical-align: top"&gt;
    &lt;td style="width: 0.25in"&gt;&#160;&lt;/td&gt;
    &lt;td style="width: 0.25in"&gt;&#x2022;&lt;/td&gt;
    &lt;td&gt;3-month price appreciation. Companies are numerically ranked by their stock&#x2019;s trailing three-month price appreciation, with a preference to those with the greatest price appreciation.&lt;/td&gt;&lt;/tr&gt;
  &lt;/table&gt;
&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0 0 0.25in"&gt;&#160;&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0 0 0.25in"&gt;&#160;&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0 0 0.25in"&gt;Growth Model. The following factors are used to evaluate
and rank the stocks within the model:&lt;/p&gt;

&lt;table cellpadding="0" cellspacing="0" style="font: 10pt/11pt Times New Roman, Times, Serif; margin-top: 0; margin-bottom: 0; width: 100%"&gt;
  &lt;tr style="vertical-align: top"&gt;
    &lt;td style="width: 0.25in"&gt;&#160;&lt;/td&gt;
    &lt;td style="width: 0.25in"&gt;&#x2022;&lt;/td&gt;
    &lt;td&gt;Price to sales ratio. Compares a company&#x2019;s market capitalization to revenue generated. Companies that have a lower price to sales ratio are assigned a higher ranking.&lt;/td&gt;&lt;/tr&gt;
  &lt;/table&gt;
&lt;table cellpadding="0" cellspacing="0" style="font: 10pt/11pt Times New Roman, Times, Serif; margin-top: 0; margin-bottom: 0; width: 100%"&gt;
  &lt;tr style="vertical-align: top"&gt;
    &lt;td style="width: 0.25in"&gt;&#160;&lt;/td&gt;
    &lt;td style="width: 0.25in"&gt;&#x2022;&lt;/td&gt;
    &lt;td&gt;Price to cash flow ratio. Compares a company&#x2019;s market capitalization to its cash flow generated. Companies that have a lower, but positive, price to cash flow ratio are assigned a higher ranking.&lt;/td&gt;&lt;/tr&gt;
  &lt;/table&gt;
&lt;table cellpadding="0" cellspacing="0" style="font: 10pt/11pt Times New Roman, Times, Serif; margin-top: 0; margin-bottom: 0; width: 100%"&gt;
  &lt;tr style="vertical-align: top"&gt;
    &lt;td style="width: 0.25in"&gt;&#160;&lt;/td&gt;
    &lt;td style="width: 0.25in"&gt;&#x2022;&lt;/td&gt;
    &lt;td&gt;Change in return on assets. Compares a company&#x2019;s current return on assets relative to a year ago. Companies that have a higher change in return on assets are assigned a higher ranking.&lt;/td&gt;&lt;/tr&gt;
  &lt;/table&gt;
&lt;table cellpadding="0" cellspacing="0" style="font: 10pt/11pt Times New Roman, Times, Serif; margin-top: 0; margin-bottom: 0; width: 100%"&gt;
  &lt;tr style="vertical-align: top"&gt;
    &lt;td style="width: 0.25in"&gt;&#160;&lt;/td&gt;
    &lt;td style="width: 0.25in"&gt;&#x2022;&lt;/td&gt;
    &lt;td&gt;6-month price appreciation. Companies are numerically ranked by their stock&#x2019;s trailing six-month price appreciation, with a preference to those with the greatest price appreciation.&lt;/td&gt;&lt;/tr&gt;
  &lt;/table&gt;
&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 0; text-indent: 0.25in"&gt;&lt;i&gt;3. Select the highest scoring stocks.&lt;/i&gt;&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0; text-indent: 0.25in"&gt;The 30 stocks with the best overall ranking
from each of the seven style classes are selected for the portfolio, subject to a maximum of six stocks from any one of the major market
sectors as determined by S&amp;amp;P&#x2019;s Global Industry Classification Standard (GICS&lt;sup&gt;&#xae;&lt;/sup&gt;). The Financials and Real Estate
sectors are combined for the sector limit purpose. If more than six stocks from any one of the major GICS&lt;sup&gt;&#xae;&lt;/sup&gt; sectors are
selected, those stocks are excluded and replaced with the next best scoring stocks which satisfy the criteria set forth above. In the
event of a tie, the stock with the better price to cash flow ratio is selected.&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 1pt 0 1pt 0.25in"&gt;Large-Cap Growth	25%&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 1pt 0 1pt 0.25in"&gt;Large-Cap Value	25%&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 1pt 0 1pt 0.25in"&gt;Mid-Cap Growth	10%&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 1pt 0 1pt 0.25in"&gt;Mid-Cap Value	10%&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 1pt 0 1pt 0.25in"&gt;Small-Cap Growth	5%&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 1pt 0 1pt 0.25in"&gt;Small-Cap Value	5%&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 1pt 0 1pt 0.25in"&gt;International	20%&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0; text-indent: 0.25in"&gt;Stocks are approximately equally weighted
within their style, taking into consideration that only whole shares will be purchased.&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0; text-indent: 0.25in"&gt;Please note that we applied the strategy
which makes up the portfolio for the Trust at a particular time. If we create additional Units of the Trust after the Initial Date of
Deposit, we will deposit the Securities originally selected by applying the strategy on the Initial Date of Deposit. This is true even
if a later application of the strategy would have resulted in the selection of different securities. In addition, companies which, based
on publicly available information as of the date the Securities were selected, are the subject of an announced business combination which
we expect will happen within 12 months of the date of this prospectus are not eligible for inclusion in the Trust&#x2019;s portfolio.&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0; text-indent: 0.25in"&gt;The Securities were selected as of the selection
date using closing market prices on such date or, if a particular market was not open for trading on such date, closing market prices
on the day immediately prior to the selection date in which such market was open. In addition, companies which, based on publicly available
information on or before their respective selection date, are subject to any of the limited circumstances which warrant removal of a Security
from the Trust as described under &#x201c;Removing Securities from the Trust&#x201d; are not eligible for inclusion in the Trust&#x2019;s
portfolio.&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 0; text-indent: 0.25in"&gt;&lt;span style="letter-spacing: -0.05pt"&gt;While not
a part of the Trust&#x2019;s portfolio selection process, the Trust also invests in &lt;/span&gt;dividend-paying securities and REITs.&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0; text-indent: 0.25in"&gt;As with any similar investments, there can
be no assurance that the objective of the Trust will be achieved. See &#x201c;Risk Factors&#x201d; for a discussion of the risks of investing
in the Trust.&lt;/p&gt;

&lt;p style="font: 10pt/11pt Times New Roman, Times, Serif; margin: 2pt 0; text-indent: 0.25in"&gt;The publisher of the S&amp;amp;P Composite 1500&lt;sup&gt;&#xae;&lt;/sup&gt;
Index is not affiliated with us and has not participated in creating the Trust or selecting the Securities for the Trust. Except as noted
herein, the index publisher has not approved of any of the information in this prospectus.&lt;/p&gt;

</fnd:NmRule35d1TermSlctnCritTextBlock>
</xbrl>
