<?xml version="1.0" encoding="utf-8"?>
<xbrl
  xmlns="http://www.xbrl.org/2003/instance"
  xmlns:dei="http://xbrl.sec.gov/dei/2023"
  xmlns:fmr="http://www.fidelity.com/20250301"
  xmlns:iso4217="http://www.xbrl.org/2003/iso4217"
  xmlns:link="http://www.xbrl.org/2003/linkbase"
  xmlns:oef="http://xbrl.sec.gov/oef/2023"
  xmlns:us-gaap="http://fasb.org/us-gaap/2023"
  xmlns:xbrldi="http://xbrl.org/2006/xbrldi"
  xmlns:xlink="http://www.w3.org/1999/xlink">
    <link:schemaRef xlink:href="fmr-20250301.xsd" xlink:type="simple"/>
    <context id="C000020486_ClassMember">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000702149</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000020486Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2024-06-30</startDate>
            <endDate>2024-12-31</endDate>
        </period>
    </context>
    <context id="C000020486_InstantMember">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000702149</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000020486Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2024-12-31</instant>
        </period>
    </context>
    <context id="C000020486_EMD_0_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000702149</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000020486Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:MaturityAxis">fmr:EMD0Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2024-12-31</instant>
        </period>
    </context>
    <context id="C000020486_EMD_1_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000702149</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000020486Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:MaturityAxis">fmr:EMD1Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2024-12-31</instant>
        </period>
    </context>
    <context id="C000020486_EMD_2_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000702149</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000020486Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:MaturityAxis">fmr:EMD2Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2024-12-31</instant>
        </period>
    </context>
    <context id="C000020486_EMD_3_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000702149</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000020486Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:MaturityAxis">fmr:EMD3Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2024-12-31</instant>
        </period>
    </context>
    <context id="C000020486_EMD_4_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000702149</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000020486Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:MaturityAxis">fmr:EMD4Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2024-12-31</instant>
        </period>
    </context>
    <context id="C000020486_EMD_5_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000702149</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000020486Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:MaturityAxis">fmr:EMD5Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2024-12-31</instant>
        </period>
    </context>
    <context id="C000020486_AA_USTreasuryObligations_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000702149</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:InvestmentTypeAxis">fmr:AAUSTreasuryObligationsMember</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000020486Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2024-12-31</instant>
        </period>
    </context>
    <context id="C000020486_AA_USGovernmentAgencyDebt_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000702149</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:InvestmentTypeAxis">fmr:AAUSGovernmentAgencyDebtMember</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000020486Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2024-12-31</instant>
        </period>
    </context>
    <context id="C000020486_AA_RepurchaseAgreements_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000702149</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:InvestmentTypeAxis">fmr:AARepurchaseAgreementsMember</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000020486Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2024-12-31</instant>
        </period>
    </context>
    <context id="Trust">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000702149</identifier>
        </entity>
        <period>
            <startDate>2024-06-30</startDate>
            <endDate>2024-12-31</endDate>
        </period>
    </context>
    <unit id="usd">
        <measure>iso4217:USD</measure>
    </unit>
    <unit id="pure">
        <measure>pure</measure>
    </unit>
    <unit id="holding">
        <measure>shares</measure>
    </unit>
    <dei:DocumentType contextRef="Trust" id="ixv-10670">N-CSRS</dei:DocumentType>
    <dei:AmendmentFlag contextRef="Trust" id="ixv-10671">false</dei:AmendmentFlag>
    <dei:EntityCentralIndexKey contextRef="Trust" id="ixv-10672">0000702149</dei:EntityCentralIndexKey>
    <dei:EntityInvCompanyType contextRef="Trust" id="ixv-10673">N-1A</dei:EntityInvCompanyType>
    <dei:EntityRegistrantName contextRef="Trust" id="ixv-10674">The North Carolina Capital Management Trust</dei:EntityRegistrantName>
    <dei:DocumentPeriodEndDate contextRef="Trust" id="ixv-96">2024-12-31</dei:DocumentPeriodEndDate>
    <oef:FundName contextRef="C000020486_ClassMember" id="ixv-108">Government Portfolio</oef:FundName>
    <oef:ClassName contextRef="C000020486_ClassMember" id="ixv-111">Government Portfolio</oef:ClassName>
    <dei:TradingSymbol contextRef="C000020486_ClassMember" id="ixv-115">NCCTX</dei:TradingSymbol>
    <oef:AnnlOrSemiAnnlStatementTextBlock contextRef="C000020486_ClassMember" id="ixv-134">This semi-annual shareholder report contains information about Government Portfolio for the period July 1, 2024 to December 31, 2024.</oef:AnnlOrSemiAnnlStatementTextBlock>
    <oef:ShareholderReportAnnualOrSemiAnnual contextRef="C000020486_ClassMember" id="ixv-136">semi-annual shareholder report</oef:ShareholderReportAnnualOrSemiAnnual>
    <oef:AddlInfoTextBlock contextRef="C000020486_ClassMember" id="ixv-141">You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-800-222-3232.</oef:AddlInfoTextBlock>
    <oef:AddlInfoWebsite contextRef="C000020486_ClassMember" id="ixv-143">fundresearch.fidelity.com/prospectus/sec</oef:AddlInfoWebsite>
    <oef:AddlInfoPhoneNumber contextRef="C000020486_ClassMember" id="ixv-146">1-800-222-3232</oef:AddlInfoPhoneNumber>
    <oef:ExpensesTextBlock contextRef="C000020486_ClassMember" id="ixv-153">&lt;span style="font-family:'Fidelity Sans';font-size:16px;color:#368627;font-style:normal;font-weight:bold;"&gt;What were your Fund costs for the last six months?&lt;/span&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;(based on hypothetical $10,000 investment)&lt;/span&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;&#160;&lt;/span&gt;&lt;/div&gt;
&lt;span style="line-height:12px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;table cellpadding="0" cellspacing="0" style="border-collapse:collapse;border-style:none;" width="100%"&gt;&lt;tr&gt;&lt;td style="width:45%; background-color:#dfe0e4;border:1px solid #dfe0e4;padding:0px 0px 0px 0px;" valign="bottom"&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:bold;"&gt;&#160;&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:24%; background-color:#dfe0e4;border:1px solid #dfe0e4;padding:0px 0px 0px 0px;" valign="bottom"&gt;&lt;div style="text-align:center;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:bold;"&gt;Costs of a $10,000 investment&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:30%; background-color:#dfe0e4;border:1px solid #dfe0e4;padding:0px 0px 0px 0px;" valign="bottom"&gt;&lt;div style="text-align:center;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:bold;"&gt;Costs paid as a percentage of a $10,000 investment &lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:1%; " valign="top"&gt;&lt;span style="line-height:12px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;&lt;td style="width:45%; border-bottom:1px solid #000000;padding:0px 0px 0px 0px;" valign="top"&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;Government Portfolio&lt;/span&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;&#160;&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:24%; border-bottom:1px solid #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:center;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;$ &lt;/span&gt;7&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;&#160;&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:30%; border-bottom:1px solid #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:center;text-align-last:auto;"&gt;0.14&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;%&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:1%; " valign="top"&gt;&lt;span style="line-height:12px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;/tr&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;</oef:ExpensesTextBlock>
    <oef:ExpensesPaidAmt
      contextRef="C000020486_ClassMember"
      decimals="0"
      id="ixv-10777"
      unitRef="usd">7</oef:ExpensesPaidAmt>
    <oef:ExpenseRatioPct
      contextRef="C000020486_ClassMember"
      decimals="INF"
      id="ixv-10778"
      unitRef="pure">0.0014</oef:ExpenseRatioPct>
    <oef:AddlFundStatisticsTextBlock contextRef="C000020486_ClassMember" id="ixv-193">&lt;span style="font-family:'Fidelity Sans';font-size:16px;color:#368627;font-style:normal;font-weight:bold;"&gt;Key Fund Statistics&lt;/span&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;(as of December 31, 2024)&lt;/span&gt;&lt;/div&gt;
&lt;div&gt;&lt;span style="font-size:11px;"&gt;&#160;&lt;/span&gt;&lt;/div&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;div style="text-align:right;text-align-last:auto;"&gt;&lt;table cellpadding="0" cellspacing="1" style="border-collapse:separate;border-style:none;margin:auto;" width="100%"&gt;&lt;tr&gt;&lt;td style="width:63%; " valign="top"&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:12px;color:#000000;font-style:normal;font-weight:bold;"&gt;KEY FACTS&lt;/span&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:bold;"&gt;&#160;&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:32%; " valign="top"&gt;&lt;span style="line-height:12px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:5%; " valign="top"&gt;&lt;span style="line-height:12px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;&lt;td style="width:63%; border-bottom:1px dashed #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;Fund Size&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:32%; border-bottom:1px dashed #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:right;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;$&lt;/span&gt;22,893,618,103&lt;/div&gt;
&lt;div style="text-align:right;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:5%; " valign="top"&gt;&lt;span style="line-height:11px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;&lt;td style="width:63%; border-bottom:1px dashed #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;Number of Holdings&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:32%; border-bottom:1px dashed #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:right;text-align-last:auto;"&gt;411&lt;/div&gt;
&lt;div style="text-align:right;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:5%; " valign="top"&gt;&lt;span style="line-height:11px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;/tr&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;</oef:AddlFundStatisticsTextBlock>
    <us-gaap:AssetsNet
      contextRef="C000020486_InstantMember"
      decimals="0"
      id="ixv-10779"
      unitRef="usd">22893618103</us-gaap:AssetsNet>
    <oef:HoldingsCount
      contextRef="C000020486_InstantMember"
      decimals="INF"
      id="ixv-10780"
      unitRef="holding">411</oef:HoldingsCount>
    <oef:HoldingsTableTextBlock contextRef="C000020486_ClassMember" id="ixv-242">
&#160;
EFFECTIVE MATURITY DIVERSIFICATION
(% of Fund's net assets)


&#160;
Days
&#160;


1-7

33.1

&#160;


8-30

29.6

&#160;


31-60

19.6

&#160;


61-90

9.7

&#160;


91-180

6.4

&#160;


&gt;180

2.3

&#160;


&#160;
&#160;




&#160;
&#160;
&#160;
U.S. Treasury Obligations

60.2


U.S. Government Agency - Debt

35.0


Repurchase Agreements

5.5




ASSET ALLOCATION (% of Fund's net assets)


&#160;



&#160;

U.S. Treasury Obligations - 60.2&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;


&#160;

U.S. Government Agency - Debt - 35.0&#160;&#160;&#160;&#160;


&#160;

Repurchase Agreements - 5.5&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;


Net Other Assets (Liabilities) - (0.7)%


&#160;






</oef:HoldingsTableTextBlock>
    <oef:PctOfNav
      contextRef="C000020486_EMD_0_Member"
      decimals="INF"
      id="ixv-10781"
      unitRef="pure">0.331</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000020486_EMD_1_Member"
      decimals="INF"
      id="ixv-10782"
      unitRef="pure">0.296</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000020486_EMD_2_Member"
      decimals="INF"
      id="ixv-10783"
      unitRef="pure">0.196</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000020486_EMD_3_Member"
      decimals="INF"
      id="ixv-10784"
      unitRef="pure">0.097</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000020486_EMD_4_Member"
      decimals="INF"
      id="ixv-10785"
      unitRef="pure">0.064</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000020486_EMD_5_Member"
      decimals="INF"
      id="ixv-10786"
      unitRef="pure">0.023</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000020486_AA_USTreasuryObligations_Member"
      decimals="INF"
      id="ixv-10787"
      unitRef="pure">0.602</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000020486_AA_USGovernmentAgencyDebt_Member"
      decimals="INF"
      id="ixv-10788"
      unitRef="pure">0.350</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000020486_AA_RepurchaseAgreements_Member"
      decimals="INF"
      id="ixv-10789"
      unitRef="pure">0.055</oef:PctOfNav>
</xbrl>
