<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.20.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>422</ContextCount>
  <ElementCount>527</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>112</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>4</UnitCount>
  <MyReports>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001000 - Document - Cover Page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/CoverPage</Role>
      <ShortName>Cover Page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001000 - Statement - Statements of Condition</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/StatementsOfCondition</Role>
      <ShortName>Statements of Condition</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1001001 - Statement - Statements of Condition (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/StatementsOfConditionParenthetical</Role>
      <ShortName>Statements of Condition (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1002000 - Statement - Statements of Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/StatementsOfOperations</Role>
      <ShortName>Statements of Operations</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1003000 - Statement - Statements of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/StatementsOfComprehensiveIncome</Role>
      <ShortName>Statements of Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1004000 - Statement - Statements of Capital</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/StatementsOfCapital</Role>
      <ShortName>Statements of Capital</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1005000 - Statement - Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/StatementsOfCashFlows</Role>
      <ShortName>Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>2106100 - Disclosure - Basis of Presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/BasisOfPresentation</Role>
      <ShortName>Basis of Presentation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2108100 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/SummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2109100 - Disclosure - Recently Issued and Adopted Accounting Guidance</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/RecentlyIssuedAndAdoptedAccountingGuidance</Role>
      <ShortName>Recently Issued and Adopted Accounting Guidance</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2110100 - Disclosure - Investments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/Investments</Role>
      <ShortName>Investments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2118100 - Disclosure - Advances</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/Advances</Role>
      <ShortName>Advances</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2119100 - Disclosure - Mortgage Loans Held for Portfolio</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/MortgageLoansHeldForPortfolio</Role>
      <ShortName>Mortgage Loans Held for Portfolio</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2123100 - Disclosure - Derivatives and Hedging Activities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/DerivativesAndHedgingActivities</Role>
      <ShortName>Derivatives and Hedging Activities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2124100 - Disclosure - Deposits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/Deposits</Role>
      <ShortName>Deposits</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2125100 - Disclosure - Consolidated Obligations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/ConsolidatedObligations</Role>
      <ShortName>Consolidated Obligations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2127100 - Disclosure - Affordable Housing Program</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/AffordableHousingProgram</Role>
      <ShortName>Affordable Housing Program</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2128100 - Disclosure - Capital</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/Capital</Role>
      <ShortName>Capital</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2129100 - Disclosure - Accumulated Other Comprehensive Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/AccumulatedOtherComprehensiveLoss</Role>
      <ShortName>Accumulated Other Comprehensive Loss</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2131100 - Disclosure - Fair Values</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/FairValues</Role>
      <ShortName>Fair Values</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2132100 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/CommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2133100 - Disclosure - Transactions with Shareholders</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/TransactionsWithShareholders</Role>
      <ShortName>Transactions with Shareholders</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2135100 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/SubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2208201 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/SummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/SummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2310301 - Disclosure - Investments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/InvestmentsTables</Role>
      <ShortName>Investments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/Investments</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2318301 - Disclosure - Advances (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/AdvancesTables</Role>
      <ShortName>Advances (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/Advances</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2319301 - Disclosure - Mortgage Loans Held for Portfolio (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/MortgageLoansHeldForPortfolioTables</Role>
      <ShortName>Mortgage Loans Held for Portfolio (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/MortgageLoansHeldForPortfolio</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2323301 - Disclosure - Derivatives and Hedging Activities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/DerivativesAndHedgingActivitiesTables</Role>
      <ShortName>Derivatives and Hedging Activities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/DerivativesAndHedgingActivities</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2324301 - Disclosure - Deposits (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/DepositsTables</Role>
      <ShortName>Deposits (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/Deposits</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2325301 - Disclosure - Consolidated Obligations (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/ConsolidatedObligationsTables</Role>
      <ShortName>Consolidated Obligations (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/ConsolidatedObligations</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2327301 - Disclosure - Affordable Housing Program (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/AffordableHousingProgramTables</Role>
      <ShortName>Affordable Housing Program (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/AffordableHousingProgram</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2328301 - Disclosure - Capital (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/CapitalTables</Role>
      <ShortName>Capital (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/Capital</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2329301 - Disclosure - Accumulated Other Comprehensive Loss (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/AccumulatedOtherComprehensiveLossTables</Role>
      <ShortName>Accumulated Other Comprehensive Loss (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/AccumulatedOtherComprehensiveLoss</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2331301 - Disclosure - Fair Values (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/FairValuesTables</Role>
      <ShortName>Fair Values (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/FairValues</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2332301 - Disclosure - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/CommitmentsAndContingenciesTables</Role>
      <ShortName>Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/CommitmentsAndContingencies</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2333301 - Disclosure - Transactions with Shareholders (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/TransactionsWithShareholdersTables</Role>
      <ShortName>Transactions with Shareholders (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/TransactionsWithShareholders</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2409401 - Disclosure - Recently Issued and Adopted Accounting Guidance Financial Instruments - Credit Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/RecentlyIssuedAndAdoptedAccountingGuidanceFinancialInstrumentsCreditLossesDetails</Role>
      <ShortName>Recently Issued and Adopted Accounting Guidance Financial Instruments - Credit Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2410402 - Disclosure - Investments Trading Securities by Major Security Type (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/InvestmentsTradingSecuritiesByMajorSecurityTypeDetails</Role>
      <ShortName>Investments Trading Securities by Major Security Type (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2410403 - Disclosure - Investments Available-for-Sale Securities by Major Security Type (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/InvestmentsAvailableForSaleSecuritiesByMajorSecurityTypeDetails</Role>
      <ShortName>Investments Available-for-Sale Securities by Major Security Type (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2410404 - Disclosure - Investments Available-for-Sale Securities in a Continuous Unrealized Loss Position (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/InvestmentsAvailableForSaleSecuritiesInContinuousUnrealizedLossPositionDetails</Role>
      <ShortName>Investments Available-for-Sale Securities in a Continuous Unrealized Loss Position (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2410405 - Disclosure - Investments Available-for-Sale Securities by Contractual Maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/InvestmentsAvailableForSaleSecuritiesByContractualMaturityDetails</Role>
      <ShortName>Investments Available-for-Sale Securities by Contractual Maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2410406 - Disclosure - Investments Held-to-Maturity Securities by Major Security Type (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/InvestmentsHeldToMaturitySecuritiesByMajorSecurityTypeDetails</Role>
      <ShortName>Investments Held-to-Maturity Securities by Major Security Type (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2410407 - Disclosure - Investments Held-to-Maturity Securities by Contractual Maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/InvestmentsHeldToMaturitySecuritiesByContractualMaturityDetails</Role>
      <ShortName>Investments Held-to-Maturity Securities by Contractual Maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2410408 - Disclosure - Investments Proceeds from Sale and Gains and Losses on Held-to-Maturity Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/InvestmentsProceedsFromSaleAndGainsAndLossesOnHeldToMaturitySecuritiesDetails</Role>
      <ShortName>Investments Proceeds from Sale and Gains and Losses on Held-to-Maturity Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2410409 - Disclosure - Investments Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/InvestmentsNarrativeDetails</Role>
      <ShortName>Investments Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2418402 - Disclosure - Advances Outstanding by Year of Contractual Maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/AdvancesOutstandingByYearOfContractualMaturityDetails</Role>
      <ShortName>Advances Outstanding by Year of Contractual Maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2418403 - Disclosure - Advances Outstanding by Year of Contractual Maturity or Next Call Date (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/AdvancesOutstandingByYearOfContractualMaturityOrNextCallDateDetails</Role>
      <ShortName>Advances Outstanding by Year of Contractual Maturity or Next Call Date (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2418404 - Disclosure - Advances Outstanding by Year of Contractual Maturity or Next Put Date (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/AdvancesOutstandingByYearOfContractualMaturityOrNextPutDateDetails</Role>
      <ShortName>Advances Outstanding by Year of Contractual Maturity or Next Put Date (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2418405 - Disclosure - Advances by Current Interest Rate Terms (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/AdvancesByCurrentInterestRateTermsDetails</Role>
      <ShortName>Advances by Current Interest Rate Terms (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2418406 - Disclosure - Advances Advances Prepayment Fees (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/AdvancesAdvancesPrepaymentFeesDetails</Role>
      <ShortName>Advances Advances Prepayment Fees (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2418407 - Disclosure - Advances - Narratives (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/AdvancesNarrativesDetails</Role>
      <ShortName>Advances - Narratives (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2419402 - Disclosure - Mortgage Loans Held for Portfolio (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/MortgageLoansHeldForPortfolioDetails</Role>
      <ShortName>Mortgage Loans Held for Portfolio (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/MortgageLoansHeldForPortfolioTables</ParentRole>
      <Position>52</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2419403 - Disclosure - Mortgage Loans Held for Portfolio by Collateral/Guarantee Type (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/MortgageLoansHeldForPortfolioByCollateralGuaranteeTypeDetails</Role>
      <ShortName>Mortgage Loans Held for Portfolio by Collateral/Guarantee Type (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2419404 - Disclosure - Credit Quality Indicator for Conventional Mortgage Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/CreditQualityIndicatorForConventionalMortgageLoansDetails</Role>
      <ShortName>Credit Quality Indicator for Conventional Mortgage Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2419405 - Disclosure - Other Delinquency Statistics (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/OtherDelinquencyStatisticsDetails</Role>
      <ShortName>Other Delinquency Statistics (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2419406 - Disclosure - Allowance for Credit Losses on Conventional Mortgage Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/AllowanceForCreditLossesOnConventionalMortgageLoansDetails</Role>
      <ShortName>Allowance for Credit Losses on Conventional Mortgage Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2419407 - Disclosure - Mortgage Loans Held for Portfolio Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/MortgageLoansHeldForPortfolioNarrativeDetails</Role>
      <ShortName>Mortgage Loans Held for Portfolio Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>2423402 - Disclosure - Derivatives in Statement of Condition (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/DerivativesInStatementOfConditionDetails</Role>
      <ShortName>Derivatives in Statement of Condition (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>2423403 - Disclosure - Derivatives in Statement of Income and Impact on Interest Income/Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/DerivativesInStatementOfIncomeAndImpactOnInterestIncomeExpenseDetails</Role>
      <ShortName>Derivatives in Statement of Income and Impact on Interest Income/Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>2423404 - Disclosure - Net Gains (Losses) on Cash Flow Hedging Relationships (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/NetGainsLossesOnCashFlowHedgingRelationshipsDetails</Role>
      <ShortName>Net Gains (Losses) on Cash Flow Hedging Relationships (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>2423405 - Disclosure - Basis Adjustments for Fair Value Hedges (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/BasisAdjustmentsForFairValueHedgesDetails</Role>
      <ShortName>Basis Adjustments for Fair Value Hedges (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>2423406 - Disclosure - Derivatives in Statement of Income and Impact on Other Income/Loss (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/DerivativesInStatementOfIncomeAndImpactOnOtherIncomeLossDetails</Role>
      <ShortName>Derivatives in Statement of Income and Impact on Other Income/Loss (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>2423407 - Disclosure - Derivatives and Hedging Activities Narratives (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/DerivativesAndHedgingActivitiesNarrativesDetails</Role>
      <ShortName>Derivatives and Hedging Activities Narratives (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>2423408 - Disclosure - Netting of Derivative Assets and Derivative Liabiities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/NettingOfDerivativeAssetsAndDerivativeLiabiitiesDetails</Role>
      <ShortName>Netting of Derivative Assets and Derivative Liabiities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>2424402 - Disclosure - Deposits Narratives (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/DepositsNarrativesDetails</Role>
      <ShortName>Deposits Narratives (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>2425402 - Disclosure - Consolidated Obligations CO Bonds Outstanding by Contractual Maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/ConsolidatedObligationsCoBondsOutstandingByContractualMaturityDetails</Role>
      <ShortName>Consolidated Obligations CO Bonds Outstanding by Contractual Maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>2425403 - Disclosure - Consolidated Obligations CO Bonds Outstanding By Call Feature (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/ConsolidatedObligationsCoBondsOutstandingByCallFeatureDetails</Role>
      <ShortName>Consolidated Obligations CO Bonds Outstanding By Call Feature (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>2425404 - Disclosure - Consolidated Obligations CO Bonds Outstanding by Contractual Maturity or Next Call Date (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/ConsolidatedObligationsCoBondsOutstandingByContractualMaturityOrNextCallDateDetails</Role>
      <ShortName>Consolidated Obligations CO Bonds Outstanding by Contractual Maturity or Next Call Date (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>2425405 - Disclosure - Consolidated Obligations CO Bonds by Interest Rate-Payment Type (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/ConsolidatedObligationsCoBondsByInterestRatePaymentTypeDetails</Role>
      <ShortName>Consolidated Obligations CO Bonds by Interest Rate-Payment Type (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>2425406 - Disclosure - Consolidated Obligations CO - Discount Notes Outstanding (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.fhlbboston.com/role/ConsolidatedObligationsCoDiscountNotesOutstandingDetails</Role>
      <ShortName>Consolidated Obligations CO - Discount Notes Outstanding (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>2427402 - Disclosure - Affordable Housing Program Narratives (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/AffordableHousingProgramNarrativesDetails</Role>
      <ShortName>Affordable Housing Program Narratives (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>2428402 - Disclosure - Capital Requirements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/CapitalRequirementsDetails</Role>
      <ShortName>Capital Requirements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>2428403 - Disclosure - Capital Narratives (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/CapitalNarrativesDetails</Role>
      <ShortName>Capital Narratives (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>2429402 - Disclosure - Accumulated Other Comprehensive Loss (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/AccumulatedOtherComprehensiveLossDetails</Role>
      <ShortName>Accumulated Other Comprehensive Loss (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/AccumulatedOtherComprehensiveLossTables</ParentRole>
      <Position>74</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>2431402 - Disclosure - Carrying Value and Fair Value of Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/CarryingValueAndFairValueOfFinancialInstrumentsDetails</Role>
      <ShortName>Carrying Value and Fair Value of Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>2431403 - Disclosure - Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/FairValueOfAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringAndNonrecurringBasisDetails</Role>
      <ShortName>Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>2431404 - Disclosure - Estimated Fair Value Level 3 Reconciliation - Roll Forward (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/EstimatedFairValueLevel3ReconciliationRollForwardDetails</Role>
      <ShortName>Estimated Fair Value Level 3 Reconciliation - Roll Forward (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>2432402 - Disclosure - Commitments and Contingencies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/CommitmentsAndContingenciesDetails</Role>
      <ShortName>Commitments and Contingencies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/CommitmentsAndContingenciesTables</ParentRole>
      <Position>78</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>2433402 - Disclosure - Transactions with Shareholders (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/TransactionsWithShareholdersDetails</Role>
      <ShortName>Transactions with Shareholders (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/TransactionsWithShareholdersTables</ParentRole>
      <Position>79</Position>
    </Report>
    <Report instance="fhlbb10q3312020.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>2435401 - Disclosure - Subsequent Events (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.fhlbboston.com/role/SubsequentEventsDetails</Role>
      <ShortName>Subsequent Events (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.fhlbboston.com/role/SubsequentEvents</ParentRole>
      <Position>80</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-Q" original="fhlbb10q3312020.htm">fhlbb10q3312020.htm</File>
    <File>ex1012020executiveinve.htm</File>
    <File>ex311q12020.htm</File>
    <File>ex312q12020.htm</File>
    <File>ex321q12020.htm</File>
    <File>ex322q12020.htm</File>
    <File>fhlbbost-20200331.xsd</File>
    <File>fhlbbost-20200331_cal.xml</File>
    <File>fhlbbost-20200331_def.xml</File>
    <File>fhlbbost-20200331_lab.xml</File>
    <File>fhlbbost-20200331_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <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>
