<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.20.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>611</ContextCount>
  <ElementCount>731</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>195</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>13</UnitCount>
  <MyReports>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>00090 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>00100 - Statement - CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/StatementConsolidatedBalanceSheets</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>00105 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/StatementConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>00200 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/StatementConsolidatedStatementsOfOperations</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF OPERATIONS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>00300 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/StatementConsolidatedStatementsOfComprehensiveLoss</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>00305 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/StatementConsolidatedStatementsOfComprehensiveLossParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>00400 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/StatementConsolidatedStatementsOfCashFlows</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>00500 - Statement - CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/StatementConsolidatedStatementsOfShareholdersEquity</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>00505 - Statement - CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/StatementConsolidatedStatementsOfShareholdersEquityParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>10101 - Disclosure - ORGANIZATION</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureOrganization</Role>
      <ShortName>ORGANIZATION</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>10201 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>10301 - Disclosure - CONCENTRATION OF RISKS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureConcentrationOfRisks</Role>
      <ShortName>CONCENTRATION OF RISKS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>10401 - Disclosure - ACQUISITION AND DISPOSAL OF SUBSIDIARIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureAcquisitionAndDisposalOfSubsidiaries</Role>
      <ShortName>ACQUISITION AND DISPOSAL OF SUBSIDIARIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>10501 - Disclosure - ACCOUNTS AND NOTES RECEIVABLE, NET</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureAccountsAndNotesReceivableNet</Role>
      <ShortName>ACCOUNTS AND NOTES RECEIVABLE, NET</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>10601 - Disclosure - SHORT-TERM INVESTMENTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureShortTermInvestments</Role>
      <ShortName>SHORT-TERM INVESTMENTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>10701 - Disclosure - PREPAID EXPENSES AND OTHER CURRENT ASSETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssets</Role>
      <ShortName>PREPAID EXPENSES AND OTHER CURRENT ASSETS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>10801 - Disclosure - PROPERTY AND EQUIPMENT, NET</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosurePropertyAndEquipmentNet</Role>
      <ShortName>PROPERTY AND EQUIPMENT, NET</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>10901 - Disclosure - INTANGIBLE ASSETS, NET</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureIntangibleAssetsNet</Role>
      <ShortName>INTANGIBLE ASSETS, NET</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>11001 - Disclosure - LAND USE RIGHTS, NET</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLandUseRightsNet</Role>
      <ShortName>LAND USE RIGHTS, NET</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>11101 - Disclosure - GOODWILL</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureGoodwill</Role>
      <ShortName>GOODWILL</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>11201 - Disclosure - LONG-TERM INVESTMENTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLongTermInvestments</Role>
      <ShortName>LONG-TERM INVESTMENTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>11301 - Disclosure - BANK BORROWINGS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureBankBorrowings</Role>
      <ShortName>BANK BORROWINGS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>11401 - Disclosure - ACCRUED EXPENSES AND OTHER PAYABLES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureAccruedExpensesAndOtherPayables</Role>
      <ShortName>ACCRUED EXPENSES AND OTHER PAYABLES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>11501 - Disclosure - LEASES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLeases</Role>
      <ShortName>LEASES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>11601 - Disclosure - BONDS PAYABLE</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureBondsPayable</Role>
      <ShortName>BONDS PAYABLE</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>11701 - Disclosure - DEFERRED GOVERNMENT GRANTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureDeferredGovernmentGrants</Role>
      <ShortName>DEFERRED GOVERNMENT GRANTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>11801 - Disclosure - TREASURY STOCK</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureTreasuryStock</Role>
      <ShortName>TREASURY STOCK</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>11901 - Disclosure - ACCUMULATED OTHER COMPREHENSIVE INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureAccumulatedOtherComprehensiveIncome</Role>
      <ShortName>ACCUMULATED OTHER COMPREHENSIVE INCOME</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>12001 - Disclosure - MAINLAND CHINA EMPLOYEE CONTRIBUTION PLAN</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureMainlandChinaEmployeeContributionPlan</Role>
      <ShortName>MAINLAND CHINA EMPLOYEE CONTRIBUTION PLAN</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>12101 - Disclosure - SHARE-BASED COMPENSATION</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureShareBasedCompensation</Role>
      <ShortName>SHARE-BASED COMPENSATION</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>12201 - Disclosure - TAXATION</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureTaxation</Role>
      <ShortName>TAXATION</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>12301 - Disclosure - RELATED PARTY TRANSACTIONS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureRelatedPartyTransactions</Role>
      <ShortName>RELATED PARTY TRANSACTIONS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>12401 - Disclosure - SEGMENT REPORTING</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureSegmentReporting</Role>
      <ShortName>SEGMENT REPORTING</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>12501 - Disclosure - RESTRICTED NET ASSETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureRestrictedNetAssets</Role>
      <ShortName>RESTRICTED NET ASSETS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>12601 - Disclosure - LOSS PER SHARE</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLossPerShare</Role>
      <ShortName>LOSS PER SHARE</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>12701 - Disclosure - SHARE CAPITAL</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureShareCapital</Role>
      <ShortName>SHARE CAPITAL</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>12801 - Disclosure - REDEEMABLE NONCONTROLLING INTERESTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureRedeemableNoncontrollingInterests</Role>
      <ShortName>REDEEMABLE NONCONTROLLING INTERESTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>12901 - Disclosure - FAIR VALUE MEASUREMENTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureFairValueMeasurements</Role>
      <ShortName>FAIR VALUE MEASUREMENTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>13001 - Disclosure - COMMITMENTS AND CONTINGENCIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>13101 - Disclosure - SUBSEQUENT EVENTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureSubsequentEvents</Role>
      <ShortName>SUBSEQUENT EVENTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>13201 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureParentCompanyOnlyCondensedFinancialInformation</Role>
      <ShortName>PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>20202 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>30103 - Disclosure - ORGANIZATION (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureOrganizationTables</Role>
      <ShortName>ORGANIZATION (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureOrganization</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>30203 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureSummaryOfSignificantAccountingPoliciesTables</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>30403 - Disclosure - ACQUISITION AND DISPOSAL OF SUBSIDIARIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureAcquisitionAndDisposalOfSubsidiariesTables</Role>
      <ShortName>ACQUISITION AND DISPOSAL OF SUBSIDIARIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureAcquisitionAndDisposalOfSubsidiaries</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>30503 - Disclosure - ACCOUNTS AND NOTES RECEIVABLE, NET (Tables)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureAccountsAndNotesReceivableNetTables</Role>
      <ShortName>ACCOUNTS AND NOTES RECEIVABLE, NET (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureAccountsAndNotesReceivableNet</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>30603 - Disclosure - SHORT-TERM INVESTMENTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureShortTermInvestmentsTables</Role>
      <ShortName>SHORT-TERM INVESTMENTS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureShortTermInvestments</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>30703 - Disclosure - PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssetsTables</Role>
      <ShortName>PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssets</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>30803 - Disclosure - PROPERTY AND EQUIPMENT, NET (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosurePropertyAndEquipmentNetTables</Role>
      <ShortName>PROPERTY AND EQUIPMENT, NET (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosurePropertyAndEquipmentNet</ParentRole>
      <Position>49</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>30903 - Disclosure - INTANGIBLE ASSETS, NET (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureIntangibleAssetsNetTables</Role>
      <ShortName>INTANGIBLE ASSETS, NET (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureIntangibleAssetsNet</ParentRole>
      <Position>50</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>31003 - Disclosure - LAND USE RIGHTS, NET (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLandUseRightsNetTables</Role>
      <ShortName>LAND USE RIGHTS, NET (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureLandUseRightsNet</ParentRole>
      <Position>51</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>31103 - Disclosure - GOODWILL (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureGoodwillTables</Role>
      <ShortName>GOODWILL (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureGoodwill</ParentRole>
      <Position>52</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>31203 - Disclosure - LONG-TERM INVESTMENTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLongTermInvestmentsTables</Role>
      <ShortName>LONG-TERM INVESTMENTS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureLongTermInvestments</ParentRole>
      <Position>53</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>31303 - Disclosure - BANK BORROWINGS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureBankBorrowingsTables</Role>
      <ShortName>BANK BORROWINGS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureBankBorrowings</ParentRole>
      <Position>54</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>31403 - Disclosure - ACCRUED EXPENSES AND OTHER PAYABLES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureAccruedExpensesAndOtherPayablesTables</Role>
      <ShortName>ACCRUED EXPENSES AND OTHER PAYABLES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureAccruedExpensesAndOtherPayables</ParentRole>
      <Position>55</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>31503 - Disclosure - LEASES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLeasesTables</Role>
      <ShortName>LEASES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureLeases</ParentRole>
      <Position>56</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>31603 - Disclosure - BONDS PAYABLE (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureBondsPayableTables</Role>
      <ShortName>BONDS PAYABLE (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureBondsPayable</ParentRole>
      <Position>57</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>31703 - Disclosure - DEFERRED GOVERNMENT GRANTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureDeferredGovernmentGrantsTables</Role>
      <ShortName>DEFERRED GOVERNMENT GRANTS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureDeferredGovernmentGrants</ParentRole>
      <Position>58</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>31903 - Disclosure - ACCUMULATED OTHER COMPREHENSIVE INCOME (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureAccumulatedOtherComprehensiveIncomeTables</Role>
      <ShortName>ACCUMULATED OTHER COMPREHENSIVE INCOME (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureAccumulatedOtherComprehensiveIncome</ParentRole>
      <Position>59</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>32103 - Disclosure - SHARE-BASED COMPENSATION (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureShareBasedCompensationTables</Role>
      <ShortName>SHARE-BASED COMPENSATION (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureShareBasedCompensation</ParentRole>
      <Position>60</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>32203 - Disclosure - TAXATION (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureTaxationTables</Role>
      <ShortName>TAXATION (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureTaxation</ParentRole>
      <Position>61</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>32303 - Disclosure - RELATED PARTY TRANSACTIONS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureRelatedPartyTransactionsTables</Role>
      <ShortName>RELATED PARTY TRANSACTIONS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureRelatedPartyTransactions</ParentRole>
      <Position>62</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>32403 - Disclosure - SEGMENT REPORTING (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureSegmentReportingTables</Role>
      <ShortName>SEGMENT REPORTING (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureSegmentReporting</ParentRole>
      <Position>63</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>32603 - Disclosure - LOSS PER SHARE (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLossPerShareTables</Role>
      <ShortName>LOSS PER SHARE (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureLossPerShare</ParentRole>
      <Position>64</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>32803 - Disclosure - REDEEMABLE NONCONTROLLING INTERESTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureRedeemableNoncontrollingInterestsTables</Role>
      <ShortName>REDEEMABLE NONCONTROLLING INTERESTS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureRedeemableNoncontrollingInterests</ParentRole>
      <Position>65</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>32903 - Disclosure - FAIR VALUE MEASUREMENTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureFairValueMeasurementsTables</Role>
      <ShortName>FAIR VALUE MEASUREMENTS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureFairValueMeasurements</ParentRole>
      <Position>66</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>33003 - Disclosure - COMMITMENTS AND CONTINGENCIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureCommitmentsAndContingenciesTables</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureCommitmentsAndContingencies</ParentRole>
      <Position>67</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>33203 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureParentCompanyOnlyCondensedFinancialInformationTables</Role>
      <ShortName>PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureParentCompanyOnlyCondensedFinancialInformation</ParentRole>
      <Position>68</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>40101 - Disclosure - ORGANIZATION - Significant subsidiaries of the Company and consolidated variable interest entities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureOrganizationSignificantSubsidiariesOfCompanyAndConsolidatedVariableInterestEntitiesDetails</Role>
      <ShortName>ORGANIZATION - Significant subsidiaries of the Company and consolidated variable interest entities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>40102 - Disclosure - ORGANIZATION - Significant subsidiaries of the Company and consolidated variable interest entities (Parenthetical) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureOrganizationSignificantSubsidiariesOfCompanyAndConsolidatedVariableInterestEntitiesParentheticalDetails</Role>
      <ShortName>ORGANIZATION - Significant subsidiaries of the Company and consolidated variable interest entities (Parenthetical) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>40103 - Disclosure - ORGANIZATION - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureOrganizationAdditionalInformationDetails</Role>
      <ShortName>ORGANIZATION - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>40104 - Disclosure - ORGANIZATION - Financial information of the consolidated VIEs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureOrganizationFinancialInformationOfConsolidatedViesDetails</Role>
      <ShortName>ORGANIZATION - Financial information of the consolidated VIEs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>40105 - Disclosure - ORGANIZATION - Financial information of the consolidated VIEs (Parenthetical) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureOrganizationFinancialInformationOfConsolidatedViesParentheticalDetails</Role>
      <ShortName>ORGANIZATION - Financial information of the consolidated VIEs (Parenthetical) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>40201 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Estimated useful lives of property and equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureSummaryOfSignificantAccountingPoliciesEstimatedUsefulLivesOfPropertyAndEquipmentDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Estimated useful lives of property and equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>40202 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Weighted average useful lives of intangible assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureSummaryOfSignificantAccountingPoliciesWeightedAverageUsefulLivesOfIntangibleAssetsDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Weighted average useful lives of intangible assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>40203 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Impairment charges associated with its long-lived assets and acquired intangibles (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureSummaryOfSignificantAccountingPoliciesImpairmentChargesAssociatedWithItsLongLivedAssetsAndAcquiredIntangiblesDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Impairment charges associated with its long-lived assets and acquired intangibles (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>40204 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Interest expenses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureSummaryOfSignificantAccountingPoliciesInterestExpensesDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Interest expenses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>40205 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>40301 - Disclosure - CONCENTRATION OF RISKS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureConcentrationOfRisksDetails</Role>
      <ShortName>CONCENTRATION OF RISKS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureConcentrationOfRisks</ParentRole>
      <Position>79</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>40401 - Disclosure - ACQUISITION AND DISPOSAL OF SUBSIDIARIES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureAcquisitionAndDisposalOfSubsidiariesDetails</Role>
      <ShortName>ACQUISITION AND DISPOSAL OF SUBSIDIARIES (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureAcquisitionAndDisposalOfSubsidiariesTables</ParentRole>
      <Position>80</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>40402 - Disclosure - ACQUISITION AND DISPOSAL OF SUBSIDIARIES - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureAcquisitionAndDisposalOfSubsidiariesAdditionalInformationDetails</Role>
      <ShortName>ACQUISITION AND DISPOSAL OF SUBSIDIARIES - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>40501 - Disclosure - ACCOUNTS AND NOTES RECEIVABLE, NET - Accounts and notes receivable and the allowance for doubtful debt (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureAccountsAndNotesReceivableNetAccountsAndNotesReceivableAndAllowanceForDoubtfulDebtDetails</Role>
      <ShortName>ACCOUNTS AND NOTES RECEIVABLE, NET - Accounts and notes receivable and the allowance for doubtful debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>40502 - Disclosure - ACCOUNTS AND NOTES RECEIVABLE, NET - Accounts and notes receivable due (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureAccountsAndNotesReceivableNetAccountsAndNotesReceivableDueDetails</Role>
      <ShortName>ACCOUNTS AND NOTES RECEIVABLE, NET - Accounts and notes receivable due (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>40601 - Disclosure - SHORT-TERM INVESTMENTS - Short-term investments consisted (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureShortTermInvestmentsShortTermInvestmentsConsistedDetails</Role>
      <ShortName>SHORT-TERM INVESTMENTS - Short-term investments consisted (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>40602 - Disclosure - SHORT-TERM INVESTMENTS - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureShortTermInvestmentsAdditionalInformationDetails</Role>
      <ShortName>SHORT-TERM INVESTMENTS - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>85</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>40701 - Disclosure - PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssetsDetails</Role>
      <ShortName>PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssetsTables</ParentRole>
      <Position>86</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>40801 - Disclosure - PROPERTY AND EQUIPMENT, NET - Property and equipment, held under capital leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosurePropertyAndEquipmentNetPropertyAndEquipmentHeldUnderCapitalLeasesDetails</Role>
      <ShortName>PROPERTY AND EQUIPMENT, NET - Property and equipment, held under capital leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>87</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>40802 - Disclosure - PROPERTY AND EQUIPMENT, NET - Depreciation expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosurePropertyAndEquipmentNetDepreciationExpenseDetails</Role>
      <ShortName>PROPERTY AND EQUIPMENT, NET - Depreciation expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>88</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>40803 - Disclosure - PROPERTY AND EQUIPMENT, NET - Carrying amounts of property and equipment held under capital leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosurePropertyAndEquipmentNetCarryingAmountsOfPropertyAndEquipmentHeldUnderCapitalLeasesDetails</Role>
      <ShortName>PROPERTY AND EQUIPMENT, NET - Carrying amounts of property and equipment held under capital leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>89</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>40804 - Disclosure - PROPERTY AND EQUIPMENT, NET - Property and equipment pledged to secure banking borrowings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosurePropertyAndEquipmentNetPropertyAndEquipmentPledgedToSecureBankingBorrowingsDetails</Role>
      <ShortName>PROPERTY AND EQUIPMENT, NET - Property and equipment pledged to secure banking borrowings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>90</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>40805 - Disclosure - PROPERTY AND EQUIPMENT, NET - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosurePropertyAndEquipmentNetAdditionalInformationDetails</Role>
      <ShortName>PROPERTY AND EQUIPMENT, NET - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>91</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>40901 - Disclosure - INTANGIBLE ASSETS, NET - Intangible assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureIntangibleAssetsNetIntangibleAssetsDetails</Role>
      <ShortName>INTANGIBLE ASSETS, NET - Intangible assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>92</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R93.htm</HtmlFileName>
      <LongName>40902 - Disclosure - INTANGIBLE ASSETS, NET - Amortization expenses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureIntangibleAssetsNetAmortizationExpensesDetails</Role>
      <ShortName>INTANGIBLE ASSETS, NET - Amortization expenses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>93</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R94.htm</HtmlFileName>
      <LongName>40903 - Disclosure - INTANGIBLE ASSETS, NET - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureIntangibleAssetsNetAdditionalInformationDetails</Role>
      <ShortName>INTANGIBLE ASSETS, NET - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>94</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R95.htm</HtmlFileName>
      <LongName>41001 - Disclosure - LAND USE RIGHTS, NET - Land use rights amortized (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLandUseRightsNetLandUseRightsAmortizedDetails</Role>
      <ShortName>LAND USE RIGHTS, NET - Land use rights amortized (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>95</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R96.htm</HtmlFileName>
      <LongName>41002 - Disclosure - LAND USE RIGHTS, NET - Land use rights pledged (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLandUseRightsNetLandUseRightsPledgedDetails</Role>
      <ShortName>LAND USE RIGHTS, NET - Land use rights pledged (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>96</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R97.htm</HtmlFileName>
      <LongName>41101 - Disclosure - GOODWILL - Carrying amount (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureGoodwillCarryingAmountDetails</Role>
      <ShortName>GOODWILL - Carrying amount (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>97</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R98.htm</HtmlFileName>
      <LongName>41102 - Disclosure - GOODWILL - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureGoodwillAdditionalInformationDetails</Role>
      <ShortName>GOODWILL - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>98</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R99.htm</HtmlFileName>
      <LongName>41201 - Disclosure - LONG-TERM INVESTMENTS - Long term investments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLongTermInvestmentsLongTermInvestmentsDetails</Role>
      <ShortName>LONG-TERM INVESTMENTS - Long term investments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>99</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R100.htm</HtmlFileName>
      <LongName>41202 - Disclosure - LONG-TERM INVESTMENTS - Equity Method Investments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLongTermInvestmentsEquityMethodInvestmentsDetails</Role>
      <ShortName>LONG-TERM INVESTMENTS - Equity Method Investments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>100</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R101.htm</HtmlFileName>
      <LongName>41203 - Disclosure - LONG-TERM INVESTMENTS - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLongTermInvestmentsAdditionalInformationDetails</Role>
      <ShortName>LONG-TERM INVESTMENTS - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>101</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R102.htm</HtmlFileName>
      <LongName>41301 - Disclosure - BANK BORROWINGS - Bank borrowings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureBankBorrowingsBankBorrowingsDetails</Role>
      <ShortName>BANK BORROWINGS - Bank borrowings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>102</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R103.htm</HtmlFileName>
      <LongName>41302 - Disclosure - BANK BORROWINGS - Unused loan facilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureBankBorrowingsUnusedLoanFacilitiesDetails</Role>
      <ShortName>BANK BORROWINGS - Unused loan facilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>103</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R104.htm</HtmlFileName>
      <LongName>41303 - Disclosure - BANK BORROWINGS - Unused loan facilities (Parenthetical) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureBankBorrowingsUnusedLoanFacilitiesParentheticalDetails</Role>
      <ShortName>BANK BORROWINGS - Unused loan facilities (Parenthetical) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>104</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R105.htm</HtmlFileName>
      <LongName>41304 - Disclosure - BANK BORROWINGS - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureBankBorrowingsAdditionalInformationDetails</Role>
      <ShortName>BANK BORROWINGS - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>105</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R106.htm</HtmlFileName>
      <LongName>41401 - Disclosure - ACCRUED EXPENSES AND OTHER PAYABLES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureAccruedExpensesAndOtherPayablesDetails</Role>
      <ShortName>ACCRUED EXPENSES AND OTHER PAYABLES (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureAccruedExpensesAndOtherPayablesTables</ParentRole>
      <Position>106</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R107.htm</HtmlFileName>
      <LongName>41501 - Disclosure - LEASES - Total lease cost (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLeasesTotalLeaseCostDetails</Role>
      <ShortName>LEASES - Total lease cost (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>107</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R108.htm</HtmlFileName>
      <LongName>41502 - Disclosure - LEASES - Other information related to leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLeasesOtherInformationRelatedToLeasesDetails</Role>
      <ShortName>LEASES - Other information related to leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>108</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R109.htm</HtmlFileName>
      <LongName>41503 - Disclosure - LEASES - Future lease payments under operating leases and finance leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLeasesFutureLeasePaymentsUnderOperatingLeasesAndFinanceLeasesDetails</Role>
      <ShortName>LEASES - Future lease payments under operating leases and finance leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>109</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R110.htm</HtmlFileName>
      <LongName>41504 - Disclosure - LEASES - Additional information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLeasesAdditionalInformationDetails</Role>
      <ShortName>LEASES - Additional information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>110</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R111.htm</HtmlFileName>
      <LongName>41601 - Disclosure - . BONDS PAYABLE - Long-Term Borrowings, Including Bonds Payable, Bank and Other Borrowings (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureBondsPayableLongTermBorrowingsIncludingBondsPayableBankAndOtherBorrowingsDetail</Role>
      <ShortName>. BONDS PAYABLE - Long-Term Borrowings, Including Bonds Payable, Bank and Other Borrowings (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>111</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R112.htm</HtmlFileName>
      <LongName>41602 - Disclosure - BONDS PAYABLE - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureBondsPayableAdditionalInformationDetails</Role>
      <ShortName>BONDS PAYABLE - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>112</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R113.htm</HtmlFileName>
      <LongName>41701 - Disclosure - DEFERRED GOVERNMENT GRANTS - Movements of Deferred Grants (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureDeferredGovernmentGrantsMovementsOfDeferredGrantsDetails</Role>
      <ShortName>DEFERRED GOVERNMENT GRANTS - Movements of Deferred Grants (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>113</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R114.htm</HtmlFileName>
      <LongName>41702 - Disclosure - DEFERRED GOVERNMENT GRANTS - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureDeferredGovernmentGrantsAdditionalInformationDetails</Role>
      <ShortName>DEFERRED GOVERNMENT GRANTS - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>114</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R115.htm</HtmlFileName>
      <LongName>41801 - Disclosure - TREASURY STOCK (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureTreasuryStockDetails</Role>
      <ShortName>TREASURY STOCK (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureTreasuryStock</ParentRole>
      <Position>115</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R116.htm</HtmlFileName>
      <LongName>41901 - Disclosure - ACCUMULATED OTHER COMPREHENSIVE INCOME (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureAccumulatedOtherComprehensiveIncomeDetails</Role>
      <ShortName>ACCUMULATED OTHER COMPREHENSIVE INCOME (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureAccumulatedOtherComprehensiveIncomeTables</ParentRole>
      <Position>116</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R117.htm</HtmlFileName>
      <LongName>42001 - Disclosure - MAINLAND CHINA EMPLOYEE CONTRIBUTION PLAN (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureMainlandChinaEmployeeContributionPlanDetails</Role>
      <ShortName>MAINLAND CHINA EMPLOYEE CONTRIBUTION PLAN (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureMainlandChinaEmployeeContributionPlan</ParentRole>
      <Position>117</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R118.htm</HtmlFileName>
      <LongName>42101 - Disclosure - SHARE-BASED COMPENSATION - Employee share options activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureShareBasedCompensationEmployeeShareOptionsActivityDetails</Role>
      <ShortName>SHARE-BASED COMPENSATION - Employee share options activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>118</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R119.htm</HtmlFileName>
      <LongName>42102 - Disclosure - SHARE-BASED COMPENSATION - Restricted stock units activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureShareBasedCompensationRestrictedStockUnitsActivityDetails</Role>
      <ShortName>SHARE-BASED COMPENSATION - Restricted stock units activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>119</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R120.htm</HtmlFileName>
      <LongName>42103 - Disclosure - SHARE-BASED COMPENSATION - Share compensation expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureShareBasedCompensationShareCompensationExpenseDetails</Role>
      <ShortName>SHARE-BASED COMPENSATION - Share compensation expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>120</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R121.htm</HtmlFileName>
      <LongName>42104 - Disclosure - SHARE BASED COMPENSATION - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureShareBasedCompensationAdditionalInformationDetails</Role>
      <ShortName>SHARE BASED COMPENSATION - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>121</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R122.htm</HtmlFileName>
      <LongName>42201 - Disclosure - TAXATION - Income Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureTaxationIncomeTaxesDetails</Role>
      <ShortName>TAXATION - Income Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>122</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R123.htm</HtmlFileName>
      <LongName>42202 - Disclosure - TAXATION - Income Tax Benefits (Expense) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureTaxationIncomeTaxBenefitsExpenseDetails</Role>
      <ShortName>TAXATION - Income Tax Benefits (Expense) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>123</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R124.htm</HtmlFileName>
      <LongName>42203 - Disclosure - TAXATION - PRC operations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureTaxationPrcOperationsDetails</Role>
      <ShortName>TAXATION - PRC operations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>124</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R125.htm</HtmlFileName>
      <LongName>42204 - Disclosure - TAXATION - PRC operations (Parenthetical) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureTaxationPrcOperationsParentheticalDetails</Role>
      <ShortName>TAXATION - PRC operations (Parenthetical) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>125</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R126.htm</HtmlFileName>
      <LongName>42206 - Disclosure - TAXATION - Deferred Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureTaxationDeferredTaxesDetails</Role>
      <ShortName>TAXATION - Deferred Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>126</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R127.htm</HtmlFileName>
      <LongName>42207 - Disclosure - TAXATION - Unrecognized Tax Benefits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureTaxationUnrecognizedTaxBenefitsDetails</Role>
      <ShortName>TAXATION - Unrecognized Tax Benefits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>127</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R128.htm</HtmlFileName>
      <LongName>42208 - Disclosure - TAXATION - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureTaxationAdditionalInformationDetails</Role>
      <ShortName>TAXATION - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>128</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R129.htm</HtmlFileName>
      <LongName>42301 - Disclosure - RELATED PARTY TRANSACTIONS - Related party transactions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureRelatedPartyTransactionsRelatedPartyTransactionsDetails</Role>
      <ShortName>RELATED PARTY TRANSACTIONS - Related party transactions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>129</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R130.htm</HtmlFileName>
      <LongName>42302 - Disclosure - RELATED PARTY TRANSACTIONS - Related party balances (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureRelatedPartyTransactionsRelatedPartyBalancesDetails</Role>
      <ShortName>RELATED PARTY TRANSACTIONS - Related party balances (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>130</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R131.htm</HtmlFileName>
      <LongName>42303 - Disclosure - RELATED PARTY TRANSACTIONS - Additional information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails</Role>
      <ShortName>RELATED PARTY TRANSACTIONS - Additional information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>131</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R132.htm</HtmlFileName>
      <LongName>42401 - Disclosure - SEGMENT REPORTING- Long lived assets and revenues (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureSegmentReportingLongLivedAssetsAndRevenuesDetails</Role>
      <ShortName>SEGMENT REPORTING- Long lived assets and revenues (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>132</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R133.htm</HtmlFileName>
      <LongName>42402 - Disclosure - SEGMENT REPORTING - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureSegmentReportingAdditionalInformationDetails</Role>
      <ShortName>SEGMENT REPORTING - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>133</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R134.htm</HtmlFileName>
      <LongName>42501 - Disclosure - RESTRICTED NET ASSETS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureRestrictedNetAssetsDetails</Role>
      <ShortName>RESTRICTED NET ASSETS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureRestrictedNetAssets</ParentRole>
      <Position>134</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R135.htm</HtmlFileName>
      <LongName>42601 - Disclosure - LOSS PER SHARE - Basic and diluted loss per share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLossPerShareBasicAndDilutedLossPerShareDetails</Role>
      <ShortName>LOSS PER SHARE - Basic and diluted loss per share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>135</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R136.htm</HtmlFileName>
      <LongName>42602 - Disclosure - LOSS PER SHARE - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureLossPerShareAdditionalInformationDetails</Role>
      <ShortName>LOSS PER SHARE - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>136</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R137.htm</HtmlFileName>
      <LongName>42701 - Disclosure - SHARE CAPITAL (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureShareCapitalDetails</Role>
      <ShortName>SHARE CAPITAL (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureShareCapital</ParentRole>
      <Position>137</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R138.htm</HtmlFileName>
      <LongName>42801 - Disclosure - REDEEMABLE NONCONTROLLING INTERESTS - Disposal of subsidiaries (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureRedeemableNoncontrollingInterestsDisposalOfSubsidiariesDetails</Role>
      <ShortName>REDEEMABLE NONCONTROLLING INTERESTS - Disposal of subsidiaries (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>138</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R139.htm</HtmlFileName>
      <LongName>42802 - Disclosure - REDEEMABLE NONCONTROLLING INTERESTS - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureRedeemableNoncontrollingInterestsAdditionalInformationDetails</Role>
      <ShortName>REDEEMABLE NONCONTROLLING INTERESTS - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>139</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R140.htm</HtmlFileName>
      <LongName>42901 - Disclosure - FAIR VALUE MEASUREMENTS - Assets and liabilities measured (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureFairValueMeasurementsAssetsAndLiabilitiesMeasuredDetails</Role>
      <ShortName>FAIR VALUE MEASUREMENTS - Assets and liabilities measured (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>140</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R141.htm</HtmlFileName>
      <LongName>42902 - Disclosure - FAIR VALUE MEASUREMENTS - Liabilities measured (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureFairValueMeasurementsLiabilitiesMeasuredDetails</Role>
      <ShortName>FAIR VALUE MEASUREMENTS - Liabilities measured (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>141</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R142.htm</HtmlFileName>
      <LongName>43001 - Disclosure - COMMITMENTS AND CONTINGENCIES - Capital and purchase commitments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureCommitmentsAndContingenciesCapitalAndPurchaseCommitmentsDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Capital and purchase commitments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>142</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R143.htm</HtmlFileName>
      <LongName>43002 - Disclosure - COMMITMENTS AND CONTINGENCIES - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureCommitmentsAndContingenciesAdditionalInformationDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>143</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R144.htm</HtmlFileName>
      <LongName>43101 - Disclosure - SUBSEQUENT EVENTS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureSubsequentEventsDetails</Role>
      <ShortName>SUBSEQUENT EVENTS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.en.21vianet.com/role/DisclosureSubsequentEvents</ParentRole>
      <Position>144</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R145.htm</HtmlFileName>
      <LongName>43201 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Condensed balance sheets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureParentCompanyOnlyCondensedFinancialInformationCondensedBalanceSheetsDetails</Role>
      <ShortName>PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Condensed balance sheets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>145</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R146.htm</HtmlFileName>
      <LongName>43202 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Condensed balance sheets (Parenthetical) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureParentCompanyOnlyCondensedFinancialInformationCondensedBalanceSheetsParentheticalDetails</Role>
      <ShortName>PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Condensed balance sheets (Parenthetical) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>146</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R147.htm</HtmlFileName>
      <LongName>43203 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION- Condensed statements of operations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureParentCompanyOnlyCondensedFinancialInformationCondensedStatementsOfOperationsDetails</Role>
      <ShortName>PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION- Condensed statements of operations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>147</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R148.htm</HtmlFileName>
      <LongName>43204 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Condensed Statement of Comprehensive Loss (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureParentCompanyOnlyCondensedFinancialInformationCondensedStatementOfComprehensiveLossDetails</Role>
      <ShortName>PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Condensed Statement of Comprehensive Loss (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>148</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R149.htm</HtmlFileName>
      <LongName>43205 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Condensed Statement of Comprehensive Loss (Parenthetical) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureParentCompanyOnlyCondensedFinancialInformationCondensedStatementOfComprehensiveLossParentheticalDetails</Role>
      <ShortName>PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Condensed Statement of Comprehensive Loss (Parenthetical) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>149</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R150.htm</HtmlFileName>
      <LongName>43206 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Condensed Statements of Cash Flows (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureParentCompanyOnlyCondensedFinancialInformationCondensedStatementsOfCashFlowsDetails</Role>
      <ShortName>PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Condensed Statements of Cash Flows (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>150</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R151.htm</HtmlFileName>
      <LongName>43207 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Related Party transactions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureParentCompanyOnlyCondensedFinancialInformationRelatedPartyTransactionsDetails</Role>
      <ShortName>PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Related Party transactions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>151</Position>
    </Report>
    <Report instance="vnet-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R152.htm</HtmlFileName>
      <LongName>43208 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.en.21vianet.com/role/DisclosureParentCompanyOnlyCondensedFinancialInformationAdditionalInformationDetails</Role>
      <ShortName>PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>152</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>vnet-20191231.xml</File>
    <File>vnet-20191231.xsd</File>
    <File>vnet-20191231_cal.xml</File>
    <File>vnet-20191231_def.xml</File>
    <File>vnet-20191231_lab.xml</File>
    <File>vnet-20191231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://xbrl.sec.gov/country/2017-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2019-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
