<?xml version="1.0" encoding="utf-8"?>
<xbrl
  xmlns="http://www.xbrl.org/2003/instance"
  xmlns:dei="http://xbrl.sec.gov/dei/2025"
  xmlns:fmr="http://www.fidelity.com/20260929"
  xmlns:iso4217="http://www.xbrl.org/2003/iso4217"
  xmlns:link="http://www.xbrl.org/2003/linkbase"
  xmlns:oef="http://xbrl.sec.gov/oef/2025"
  xmlns:us-gaap="http://fasb.org/us-gaap/2025"
  xmlns:xbrldi="http://xbrl.org/2006/xbrldi"
  xmlns:xlink="http://www.w3.org/1999/xlink">
    <link:schemaRef xlink:href="fmr-20260929.xsd" xlink:type="simple"/>
    <context id="C000019282_ClassMember">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_LG_ClassMember_11YR">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_LG_ClassMember_11YRMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2015-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_ClassMember_AsOf_2016">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_ClassMember_AsOf_2016Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_ClassMember_AsOf_2017">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_ClassMember_AsOf_2017Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_ClassMember_AsOf_2018">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_ClassMember_AsOf_2018Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_ClassMember_AsOf_2019">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_ClassMember_AsOf_2019Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_ClassMember_AsOf_2020">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_ClassMember_AsOf_2020Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_ClassMember_AsOf_2021">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_ClassMember_AsOf_2021Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_ClassMember_AsOf_2022">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_ClassMember_AsOf_2022Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_ClassMember_AsOf_2023">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_ClassMember_AsOf_2023Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_ClassMember_AsOf_2024">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_ClassMember_AsOf_2024Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_ClassMember_AsOf_2025">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_ClassMember_AsOf_2025Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_ClassMember_AsOf_2026">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_ClassMember_AsOf_2026Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_LG_1_AdditionalIndexMember_11YR">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_LG_1_AdditionalIndexMember_11YRMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2015-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_1_AdditionalIndexMember_AsOf_2016">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_1_AdditionalIndexMember_AsOf_2016Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_1_AdditionalIndexMember_AsOf_2017">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_1_AdditionalIndexMember_AsOf_2017Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_1_AdditionalIndexMember_AsOf_2018">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_1_AdditionalIndexMember_AsOf_2018Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_1_AdditionalIndexMember_AsOf_2019">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_1_AdditionalIndexMember_AsOf_2019Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_1_AdditionalIndexMember_AsOf_2020">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_1_AdditionalIndexMember_AsOf_2020Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_1_AdditionalIndexMember_AsOf_2021">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_1_AdditionalIndexMember_AsOf_2021Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_1_AdditionalIndexMember_AsOf_2022">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_1_AdditionalIndexMember_AsOf_2022Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_1_AdditionalIndexMember_AsOf_2023">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_1_AdditionalIndexMember_AsOf_2023Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_1_AdditionalIndexMember_AsOf_2024">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_1_AdditionalIndexMember_AsOf_2024Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_1_AdditionalIndexMember_AsOf_2025">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_1_AdditionalIndexMember_AsOf_2025Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_1_AdditionalIndexMember_AsOf_2026">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_1_AdditionalIndexMember_AsOf_2026Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_LG_2_AdditionalIndexMember_11YR">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_LG_2_AdditionalIndexMember_11YRMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2015-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_2_AdditionalIndexMember_AsOf_2016">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_2_AdditionalIndexMember_AsOf_2016Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_2_AdditionalIndexMember_AsOf_2017">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_2_AdditionalIndexMember_AsOf_2017Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_2_AdditionalIndexMember_AsOf_2018">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_2_AdditionalIndexMember_AsOf_2018Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_2_AdditionalIndexMember_AsOf_2019">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_2_AdditionalIndexMember_AsOf_2019Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_2_AdditionalIndexMember_AsOf_2020">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_2_AdditionalIndexMember_AsOf_2020Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_2_AdditionalIndexMember_AsOf_2021">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_2_AdditionalIndexMember_AsOf_2021Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_2_AdditionalIndexMember_AsOf_2022">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_2_AdditionalIndexMember_AsOf_2022Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_2_AdditionalIndexMember_AsOf_2023">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_2_AdditionalIndexMember_AsOf_2023Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_2_AdditionalIndexMember_AsOf_2024">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_2_AdditionalIndexMember_AsOf_2024Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_2_AdditionalIndexMember_AsOf_2025">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_2_AdditionalIndexMember_AsOf_2025Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_2_AdditionalIndexMember_AsOf_2026">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_2_AdditionalIndexMember_AsOf_2026Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_NoLoadClassMember_1YR">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_NoLoadClassMember_1YRMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_NoLoadClassMember_5YR">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_NoLoadClassMember_5YRMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2021-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_NoLoadClassMember_10YR">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_NoLoadClassMember_10YRMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2016-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_0_AdditionalIndexMember_1YR">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_0_AdditionalIndexMember_1YRMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_0_AdditionalIndexMember_5YR">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_0_AdditionalIndexMember_5YRMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2021-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_0_AdditionalIndexMember_10YR">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:AdditionalIndexAxis">fmr:C000019282_0_AdditionalIndexMember_10YRMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2016-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_1_BBIndexMember_1YR">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:BroadBasedIndexAxis">fmr:C000019282_1_BBIndexMember_1YRMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_1_BBIndexMember_5YR">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:BroadBasedIndexAxis">fmr:C000019282_1_BBIndexMember_5YRMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2021-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_1_BBIndexMember_10YR">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:BroadBasedIndexAxis">fmr:C000019282_1_BBIndexMember_10YRMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2016-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <context id="C000019282_InstantMember">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_CD_0_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:OtherCategory1Axis">fmr:CD0Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_CD_1_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:OtherCategory1Axis">fmr:CD1Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_CD_2_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:OtherCategory1Axis">fmr:CD2Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_CD_3_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:OtherCategory1Axis">fmr:CD3Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_CD_4_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:OtherCategory1Axis">fmr:CD4Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_CD_5_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:OtherCategory1Axis">fmr:CD5Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_CD_6_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:OtherCategory1Axis">fmr:CD6Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_CD_7_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:OtherCategory1Axis">fmr:CD7Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_CD_8_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:OtherCategory1Axis">fmr:CD8Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_CD_9_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:OtherCategory1Axis">fmr:CD9Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_AA_USGovernmentAgencyMortgageSecurities_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:InvestmentTypeAxis">fmr:AAUSGovernmentAgencyMortgageSecuritiesMember</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_AA_CMOsandOtherMortgageRelatedSecurities_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:InvestmentTypeAxis">fmr:AACMOsandOtherMortgageRelatedSecuritiesMember</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_AA_USTreasuryObligations_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:InvestmentTypeAxis">fmr:AAUSTreasuryObligationsMember</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_AA_Options_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:InvestmentTypeAxis">fmr:AAOptionsMember</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_TH_0_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:LargestHoldingAxis">fmr:TH0Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_TH_1_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:LargestHoldingAxis">fmr:TH1Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_TH_2_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:LargestHoldingAxis">fmr:TH2Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_TH_3_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:LargestHoldingAxis">fmr:TH3Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_TH_4_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:LargestHoldingAxis">fmr:TH4Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_TH_5_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:LargestHoldingAxis">fmr:TH5Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_TH_6_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:LargestHoldingAxis">fmr:TH6Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_TH_7_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:LargestHoldingAxis">fmr:TH7Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_TH_8_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:LargestHoldingAxis">fmr:TH8Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="C000019282_TH_9_Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
            <segment>
                <xbrldi:explicitMember dimension="oef:ClassAxis">fmr:C000019282Member</xbrldi:explicitMember>
                <xbrldi:explicitMember dimension="oef:LargestHoldingAxis">fmr:TH9Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <instant>2026-07-31</instant>
        </period>
    </context>
    <context id="Trust">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000751199</identifier>
        </entity>
        <period>
            <startDate>2025-07-31</startDate>
            <endDate>2026-07-31</endDate>
        </period>
    </context>
    <unit id="usd">
        <measure>iso4217:USD</measure>
    </unit>
    <unit id="pure">
        <measure>pure</measure>
    </unit>
    <unit id="holding">
        <measure>shares</measure>
    </unit>
    <dei:DocumentType contextRef="Trust" id="ixv-31750">N-CSR</dei:DocumentType>
    <dei:AmendmentFlag contextRef="Trust" id="ixv-31751">false</dei:AmendmentFlag>
    <dei:EntityCentralIndexKey contextRef="Trust" id="ixv-31752">0000751199</dei:EntityCentralIndexKey>
    <dei:EntityInvCompanyType contextRef="Trust" id="ixv-31753">N-1A</dei:EntityInvCompanyType>
    <dei:EntityRegistrantName contextRef="Trust" id="ixv-31754">Fidelity Income Fund</dei:EntityRegistrantName>
    <dei:DocumentPeriodEndDate contextRef="Trust" id="ixv-98">2026-07-31</dei:DocumentPeriodEndDate>
    <oef:FundName contextRef="C000019282_ClassMember" id="ixv-110">Fidelity&#xae; GNMA Fund</oef:FundName>
    <oef:ClassName contextRef="C000019282_ClassMember" id="ixv-113">Fidelity&#xae; GNMA Fund</oef:ClassName>
    <dei:TradingSymbol contextRef="C000019282_ClassMember" id="ixv-117">FGMNX</dei:TradingSymbol>
    <oef:AnnlOrSemiAnnlStatementTextBlock contextRef="C000019282_ClassMember" id="ixv-136">This annual shareholder report contains information about Fidelity&#xae; GNMA Fund for the period August 1, 2025 to July 31, 2026.</oef:AnnlOrSemiAnnlStatementTextBlock>
    <oef:ShareholderReportAnnualOrSemiAnnual contextRef="C000019282_ClassMember" id="ixv-138">annual shareholder report</oef:ShareholderReportAnnualOrSemiAnnual>
    <oef:AddlInfoTextBlock contextRef="C000019282_ClassMember" id="ixv-143">You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-800-544-8544 or by sending an e-mail to fidfunddocuments@fidelity.com.</oef:AddlInfoTextBlock>
    <oef:AddlInfoWebsite contextRef="C000019282_ClassMember" id="ixv-145">fundresearch.fidelity.com/prospectus/sec</oef:AddlInfoWebsite>
    <oef:AddlInfoPhoneNumber contextRef="C000019282_ClassMember" id="ixv-148">1-800-544-8544</oef:AddlInfoPhoneNumber>
    <oef:AddlInfoEmail contextRef="C000019282_ClassMember" id="ixv-151">fidfunddocuments@fidelity.com</oef:AddlInfoEmail>
    <oef:ExpensesTextBlock contextRef="C000019282_ClassMember" id="ixv-158">&lt;span style="font-family:'Fidelity Sans';font-size:16px;color:#368627;font-style:normal;font-weight:bold;"&gt;What were your Fund costs for the last year?&lt;/span&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;(based on hypothetical $10,000 investment)&lt;/span&gt;&lt;/div&gt;
&lt;div&gt;&lt;span style="font-size:11px;"&gt;&#160;&lt;/span&gt;&lt;/div&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:12px;color:#000000;font-style:normal;font-weight:bold;"&gt;FUND COST (PREVIOUS YEAR)&lt;/span&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;table cellpadding="0" cellspacing="0" style="border-collapse:collapse;border-style:none;" width="100%"&gt;&lt;tr&gt;&lt;td style="width:51%; background-color:#dfe0e4;border:1px solid #dfe0e4;padding:0px 0px 0px 0px;" valign="bottom"&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:bold;"&gt;&#160;&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:21%; background-color:#dfe0e4;border:1px solid #dfe0e4;padding:0px 0px 0px 0px;" valign="bottom"&gt;&lt;div style="text-align:center;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:bold;"&gt;Costs of a $10,000 investment&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:27%; background-color:#dfe0e4;border:1px solid #dfe0e4;padding:0px 0px 0px 0px;" valign="bottom"&gt;&lt;div style="text-align:center;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:bold;"&gt;Costs paid as a percentage of a $10,000 investment &lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:1%; " valign="top"&gt;&lt;span style="line-height:12px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;&lt;td style="width:51%; border-bottom:1px solid #000000;padding:0px 0px 0px 0px;" valign="top"&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:12px;color:#000000;font-style:normal;font-weight:normal;"&gt;Fidelity&#xae; GNMA Fund&lt;/span&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;&#160;&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:21%; border-bottom:1px solid #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:center;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;$&lt;/span&gt;&lt;span style="font-family:'Fidelity Sans';font-size:12px;color:#000000;font-style:normal;font-weight:normal;"&gt;&#160;&lt;/span&gt;46&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;&#160;&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:27%; border-bottom:1px solid #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:center;text-align-last:auto;"&gt;0.45&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;%&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:1%; " valign="top"&gt;&lt;span style="line-height:12px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;/tr&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;</oef:ExpensesTextBlock>
    <oef:ExpensesPaidAmt
      contextRef="C000019282_ClassMember"
      decimals="0"
      id="ixv-32337"
      unitRef="usd">46</oef:ExpensesPaidAmt>
    <oef:ExpenseRatioPct
      contextRef="C000019282_ClassMember"
      decimals="INF"
      id="ixv-32338"
      unitRef="pure">0.0045</oef:ExpenseRatioPct>
    <oef:FactorsAffectingPerfTextBlock contextRef="C000019282_ClassMember" id="ixv-201">&lt;span style="font-family:'Fidelity Sans';font-size:16px;color:#368627;font-style:normal;font-weight:bold;"&gt;What affected the Fund's performance this period?&lt;/span&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:bold;"&gt;&#160;&lt;/span&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;text-indent:-24px;margin-bottom:2px;margin-left:24px;margin-top:5px;margin-right:0px;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:12px;color:#000000;font-style:normal;font-weight:normal;"&gt;&#x2022;&lt;span style="padding-right:10px"&gt;&lt;/span&gt;U.S. taxable investment-grade bonds achieved a solid gain for the 12 months ending July 31, 2026, buoyed by three policy interest-rate cuts by the Federal Reserve in late 2025, but pulled down since then by rising bond yields, particularly for the 10-year U.S. Treasury, which serves as a benchmark for many U.S. borrowing rates.&#160;&lt;/span&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;text-indent:-24px;margin-bottom:2px;margin-left:24px;margin-top:5px;margin-right:0px;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:12px;color:#000000;font-style:normal;font-weight:normal;"&gt;&#x2022;&lt;span style="padding-right:10px"&gt;&lt;/span&gt;Against this backdrop, overall positioning among Ginnie Mae securities contributed to performance versus the benchmark Bloomberg GNMA Index for the fiscal year, with the fund's holdings benefiting from spread tightening and a carry advantage (that is, the portfolio earned more income than the benchmark average).&#160;&lt;/span&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;text-indent:-24px;margin-bottom:2px;margin-left:24px;margin-top:5px;margin-right:0px;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:12px;color:#000000;font-style:normal;font-weight:normal;"&gt;&#x2022;&lt;span style="padding-right:10px"&gt;&lt;/span&gt;Specifically, the fund's overweight in GNMAs with coupons of 2.0% and 2.5% helped, given that they outpaced the benchmark.&lt;/span&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;text-indent:-24px;margin-bottom:2px;margin-left:24px;margin-top:5px;margin-right:0px;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:12px;color:#000000;font-style:normal;font-weight:normal;"&gt;&#x2022;&lt;span style="padding-right:10px"&gt;&lt;/span&gt;Lack of exposure to recent-issue GNMA 3.5% coupon bonds that included builder buy-down collateral also boosted relative performance.&#160;&lt;/span&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;text-indent:-24px;margin-bottom:2px;margin-left:24px;margin-top:5px;margin-right:0px;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:12px;color:#000000;font-style:normal;font-weight:normal;"&gt;&#x2022;&lt;span style="padding-right:10px"&gt;&lt;/span&gt;Elsewhere, non-benchmark exposure to higher-coupon Fannie Mae and Freddie Mac securities, as well as to Freddie Mac commercial mortgage-backed securities, was beneficial.&lt;/span&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;text-indent:-24px;margin-bottom:2px;margin-left:24px;margin-top:5px;margin-right:0px;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:12px;color:#000000;font-style:normal;font-weight:normal;"&gt;&#x2022;&lt;span style="padding-right:10px"&gt;&lt;/span&gt;In contrast, the portfolio had more interest-rate sensitivity (as measured by its longer duration) than the benchmark, which detracted from relative performance as rates rose over the past 12 months.&lt;/span&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;</oef:FactorsAffectingPerfTextBlock>
    <oef:LineGraphTableTextBlock contextRef="C000019282_ClassMember" id="ixv-225">How did the Fund perform over the past 10 years?

 &#160;&#160;
CUMULATIVE PERFORMANCE
July 31, 2016 through July 31, 2026. 
Initial investment of $10,000.
Fidelity&#xae; GNMA Fund


$10,000

$10,019


$9,948


$10,549


$11,046


$11,076


$10,390


$9,934


$10,448


$10,785


$11,247



Bloomberg GNMA Index


$10,000

$10,003


$9,969


$10,608


$11,115


$11,069


$10,447


$10,010


$10,477


$10,821


$11,263



Bloomberg U.S. Aggregate Bond Index


$10,000

$9,949


$9,869


$10,666


$11,746


$11,664


$10,600


$10,243


$10,766


$11,130


$11,431



&#160;

2016

2017

2018

2019

2020

2021

2022

2023

2024

2025

2026









&#160;
</oef:LineGraphTableTextBlock>
    <oef:LineGraphAndTableMeasureName contextRef="C000019282_LG_ClassMember_11YR" id="ixv-244">&lt;span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;"&gt;Fidelity&#xae; GNMA Fund&lt;/span&gt;</oef:LineGraphAndTableMeasureName>
    <oef:AccmVal
      contextRef="C000019282_ClassMember_AsOf_2016"
      decimals="0"
      id="ixv-32339"
      unitRef="usd">10000</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_ClassMember_AsOf_2017"
      decimals="0"
      id="ixv-32340"
      unitRef="usd">10019</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_ClassMember_AsOf_2018"
      decimals="0"
      id="ixv-32341"
      unitRef="usd">9948</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_ClassMember_AsOf_2019"
      decimals="0"
      id="ixv-32342"
      unitRef="usd">10549</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_ClassMember_AsOf_2020"
      decimals="0"
      id="ixv-32343"
      unitRef="usd">11046</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_ClassMember_AsOf_2021"
      decimals="0"
      id="ixv-32344"
      unitRef="usd">11076</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_ClassMember_AsOf_2022"
      decimals="0"
      id="ixv-32345"
      unitRef="usd">10390</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_ClassMember_AsOf_2023"
      decimals="0"
      id="ixv-32346"
      unitRef="usd">9934</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_ClassMember_AsOf_2024"
      decimals="0"
      id="ixv-32347"
      unitRef="usd">10448</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_ClassMember_AsOf_2025"
      decimals="0"
      id="ixv-32348"
      unitRef="usd">10785</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_ClassMember_AsOf_2026"
      decimals="0"
      id="ixv-32349"
      unitRef="usd">11247</oef:AccmVal>
    <oef:LineGraphAndTableMeasureName
      contextRef="C000019282_LG_1_AdditionalIndexMember_11YR"
      id="ixv-293">&lt;span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;"&gt;Bloomberg GNMA Index&lt;/span&gt;</oef:LineGraphAndTableMeasureName>
    <oef:AccmVal
      contextRef="C000019282_1_AdditionalIndexMember_AsOf_2016"
      decimals="0"
      id="ixv-32350"
      unitRef="usd">10000</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_1_AdditionalIndexMember_AsOf_2017"
      decimals="0"
      id="ixv-32351"
      unitRef="usd">10003</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_1_AdditionalIndexMember_AsOf_2018"
      decimals="0"
      id="ixv-32352"
      unitRef="usd">9969</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_1_AdditionalIndexMember_AsOf_2019"
      decimals="0"
      id="ixv-32353"
      unitRef="usd">10608</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_1_AdditionalIndexMember_AsOf_2020"
      decimals="0"
      id="ixv-32354"
      unitRef="usd">11115</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_1_AdditionalIndexMember_AsOf_2021"
      decimals="0"
      id="ixv-32355"
      unitRef="usd">11069</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_1_AdditionalIndexMember_AsOf_2022"
      decimals="0"
      id="ixv-32356"
      unitRef="usd">10447</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_1_AdditionalIndexMember_AsOf_2023"
      decimals="0"
      id="ixv-32357"
      unitRef="usd">10010</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_1_AdditionalIndexMember_AsOf_2024"
      decimals="0"
      id="ixv-32358"
      unitRef="usd">10477</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_1_AdditionalIndexMember_AsOf_2025"
      decimals="0"
      id="ixv-32359"
      unitRef="usd">10821</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_1_AdditionalIndexMember_AsOf_2026"
      decimals="0"
      id="ixv-32360"
      unitRef="usd">11263</oef:AccmVal>
    <oef:LineGraphAndTableMeasureName
      contextRef="C000019282_LG_2_AdditionalIndexMember_11YR"
      id="ixv-342">&lt;span style="font-family:'Fidelity Sans';font-size:9px;color:#000000;font-style:normal;font-weight:normal;"&gt;Bloomberg U.S. Aggregate Bond Index&lt;/span&gt;</oef:LineGraphAndTableMeasureName>
    <oef:AccmVal
      contextRef="C000019282_2_AdditionalIndexMember_AsOf_2016"
      decimals="0"
      id="ixv-32361"
      unitRef="usd">10000</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_2_AdditionalIndexMember_AsOf_2017"
      decimals="0"
      id="ixv-32362"
      unitRef="usd">9949</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_2_AdditionalIndexMember_AsOf_2018"
      decimals="0"
      id="ixv-32363"
      unitRef="usd">9869</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_2_AdditionalIndexMember_AsOf_2019"
      decimals="0"
      id="ixv-32364"
      unitRef="usd">10666</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_2_AdditionalIndexMember_AsOf_2020"
      decimals="0"
      id="ixv-32365"
      unitRef="usd">11746</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_2_AdditionalIndexMember_AsOf_2021"
      decimals="0"
      id="ixv-32366"
      unitRef="usd">11664</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_2_AdditionalIndexMember_AsOf_2022"
      decimals="0"
      id="ixv-32367"
      unitRef="usd">10600</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_2_AdditionalIndexMember_AsOf_2023"
      decimals="0"
      id="ixv-32368"
      unitRef="usd">10243</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_2_AdditionalIndexMember_AsOf_2024"
      decimals="0"
      id="ixv-32369"
      unitRef="usd">10766</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_2_AdditionalIndexMember_AsOf_2025"
      decimals="0"
      id="ixv-32370"
      unitRef="usd">11130</oef:AccmVal>
    <oef:AccmVal
      contextRef="C000019282_2_AdditionalIndexMember_AsOf_2026"
      decimals="0"
      id="ixv-32371"
      unitRef="usd">11431</oef:AccmVal>
    <oef:AvgAnnlRtrTableTextBlock contextRef="C000019282_ClassMember" id="ixv-443">AVERAGE ANNUAL TOTAL RETURNS:

&#160;

1 Year

5 Year

10 Year


Fidelity&#xae; GNMA Fund

4.28%

0.31%

1.18%


Bloomberg GNMA Index

4.09%


0.35%


1.20%


Bloomberg U.S. Aggregate Bond Index

2.71%


-0.40%


1.35%




&#160;
&#160;
Visit www.fidelity.com for more recent performance information.&#160;

&#160;


The Fund's past performance is not a good predictor of the Fund's future performance. &#160;The graph and table do not reflect the deduction of taxes that a shareholder would pay on fund distributions or redemption of fund shares.





</oef:AvgAnnlRtrTableTextBlock>
    <oef:AvgAnnlRtrPct
      contextRef="C000019282_NoLoadClassMember_1YR"
      decimals="INF"
      id="ixv-32372"
      unitRef="pure">0.0428</oef:AvgAnnlRtrPct>
    <oef:AvgAnnlRtrPct
      contextRef="C000019282_NoLoadClassMember_5YR"
      decimals="INF"
      id="ixv-32373"
      unitRef="pure">0.0031</oef:AvgAnnlRtrPct>
    <oef:AvgAnnlRtrPct
      contextRef="C000019282_NoLoadClassMember_10YR"
      decimals="INF"
      id="ixv-32374"
      unitRef="pure">0.0118</oef:AvgAnnlRtrPct>
    <oef:AvgAnnlRtrPct
      contextRef="C000019282_0_AdditionalIndexMember_1YR"
      decimals="INF"
      id="ixv-32375"
      unitRef="pure">0.0409</oef:AvgAnnlRtrPct>
    <oef:AvgAnnlRtrPct
      contextRef="C000019282_0_AdditionalIndexMember_5YR"
      decimals="INF"
      id="ixv-32376"
      unitRef="pure">0.0035</oef:AvgAnnlRtrPct>
    <oef:AvgAnnlRtrPct
      contextRef="C000019282_0_AdditionalIndexMember_10YR"
      decimals="INF"
      id="ixv-32377"
      unitRef="pure">0.0120</oef:AvgAnnlRtrPct>
    <oef:AvgAnnlRtrPct
      contextRef="C000019282_1_BBIndexMember_1YR"
      decimals="INF"
      id="ixv-32378"
      unitRef="pure">0.0271</oef:AvgAnnlRtrPct>
    <oef:AvgAnnlRtrPct
      contextRef="C000019282_1_BBIndexMember_5YR"
      decimals="INF"
      id="ixv-32379"
      unitRef="pure">-0.0040</oef:AvgAnnlRtrPct>
    <oef:AvgAnnlRtrPct
      contextRef="C000019282_1_BBIndexMember_10YR"
      decimals="INF"
      id="ixv-32380"
      unitRef="pure">0.0135</oef:AvgAnnlRtrPct>
    <oef:UpdPerfInfoLocationTextBlock contextRef="C000019282_ClassMember" id="ixv-514">&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;Visit &lt;/span&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:bold;"&gt;www.fidelity.com&lt;/span&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt; for more recent performance information.&lt;/span&gt;</oef:UpdPerfInfoLocationTextBlock>
    <oef:PerformancePastDoesNotIndicateFuture contextRef="C000019282_ClassMember" id="ixv-526">&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:italic;font-weight:normal;"&gt;The Fund's past performance is not a good predictor of the Fund's future performance.&lt;/span&gt;</oef:PerformancePastDoesNotIndicateFuture>
    <oef:NoDeductionOfTaxesTextBlock contextRef="C000019282_ClassMember" id="ixv-530">&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;The graph and table do not reflect the deduction of taxes that a shareholder would pay on fund distributions or redemption of fund shares.&lt;/span&gt;</oef:NoDeductionOfTaxesTextBlock>
    <oef:AddlFundStatisticsTextBlock contextRef="C000019282_ClassMember" id="ixv-536">&lt;span style="font-family:'Fidelity Sans';font-size:16px;color:#368627;font-style:normal;font-weight:bold;"&gt;Key Fund Statistics&lt;/span&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;(as of July 31, 2026)&lt;/span&gt;&lt;/div&gt;
&lt;div&gt;&lt;span style="font-size:11px;"&gt;&#160;&lt;/span&gt;&lt;/div&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;div style="text-align:right;text-align-last:auto;"&gt;&lt;table cellpadding="0" cellspacing="1" style="border-collapse:separate;border-style:none;margin:auto;" width="100%"&gt;&lt;tr&gt;&lt;td style="width:63%; " valign="top"&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:12px;color:#000000;font-style:normal;font-weight:bold;"&gt;KEY FACTS&lt;/span&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:bold;"&gt; &lt;span&gt;&#160;&lt;/span&gt;&lt;/span&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:32%; " valign="top"&gt;&lt;span style="line-height:12px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:5%; " valign="top"&gt;&lt;span style="line-height:12px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;&lt;td style="width:63%; border-bottom:1px dashed #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;Fund Size&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:32%; border-bottom:1px dashed #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:right;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;$&lt;/span&gt;1,708,660,349&lt;/div&gt;
&lt;div style="text-align:right;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:5%; " valign="top"&gt;&lt;span style="line-height:11px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;&lt;td style="width:63%; border-bottom:1px dashed #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;Number of Holdings&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:32%; border-bottom:1px dashed #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:right;text-align-last:auto;"&gt;1,907&lt;/div&gt;
&lt;div style="text-align:right;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:5%; " valign="top"&gt;&lt;span style="line-height:11px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;&lt;td style="width:63%; border-bottom:1px dashed #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;Total Advisory Fee&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:32%; border-bottom:1px dashed #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:right;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;$&lt;/span&gt;4,934,845&lt;/div&gt;
&lt;div style="text-align:right;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:5%; " valign="middle"&gt;&lt;span style="line-height:11px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;&lt;td style="width:63%; border-bottom:1px dashed #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;Portfolio Turnover&lt;/span&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:32%; border-bottom:1px dashed #000000;padding:0px 0px 0px 0px;" valign="middle"&gt;&lt;div style="text-align:right;text-align-last:auto;"&gt;620&lt;span style="font-family:'Fidelity Sans';font-size:11px;color:#000000;font-style:normal;font-weight:normal;"&gt;%&lt;/span&gt;&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;td style="width:5%; " valign="top"&gt;&lt;span style="line-height:11px;"&gt;&#160;&lt;/span&gt;&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;
&lt;/td&gt;
&lt;/tr&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;div style="text-align:left;text-align-last:auto;"&gt;&lt;/div&gt;</oef:AddlFundStatisticsTextBlock>
    <us-gaap:AssetsNet
      contextRef="C000019282_InstantMember"
      decimals="0"
      id="ixv-32381"
      unitRef="usd">1708660349</us-gaap:AssetsNet>
    <oef:HoldingsCount
      contextRef="C000019282_InstantMember"
      decimals="INF"
      id="ixv-32382"
      unitRef="holding">1907</oef:HoldingsCount>
    <oef:AdvisoryFeesPaidAmt
      contextRef="C000019282_ClassMember"
      decimals="0"
      id="ixv-32383"
      unitRef="usd">4934845</oef:AdvisoryFeesPaidAmt>
    <us-gaap:InvestmentCompanyPortfolioTurnover
      contextRef="C000019282_ClassMember"
      decimals="INF"
      id="ixv-32384"
      unitRef="pure">6.20</us-gaap:InvestmentCompanyPortfolioTurnover>
    <oef:HoldingsTableTextBlock contextRef="C000019282_ClassMember" id="ixv-611">
&#160;
COUPON DISTRIBUTION 
(% of Fund's net assets)


0.01 - 0.99%

0.0

&#160;


1 - 1.99%

0.4

&#160;


2 - 2.99%

30.3

&#160;


3 - 3.99%

32.0

&#160;


4 - 4.99%

18.1

&#160;


5 - 5.99%

25.8

&#160;


6 - 6.99%

11.0

&#160;


7 - 7.99%

0.0

&#160;


8 - 8.99%

0.0

&#160;


17 - 17.99%

0.0

&#160;




&#160;
&#160;
&#160;
U.S. Government Agency - Mortgage Securities

92.2


CMOs and Other Mortgage Related Securities

15.7


U.S. Treasury Obligations

9.7


Options

0.2




ASSET ALLOCATION (% of Fund's net assets)


&#160;



&#160;

U.S. Government Agency - Mortgage Securities - 92.2


&#160;

CMOs and Other Mortgage Related Securities - 15.7


&#160;

U.S. Treasury Obligations - 9.7&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;


&#160;

Options - 0.2&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;


Short-Term Investments and Net Other Assets (Liabilities) - (17.8)%


&#160;






</oef:HoldingsTableTextBlock>
    <oef:PctOfNav
      contextRef="C000019282_CD_0_Member"
      decimals="INF"
      id="ixv-32385"
      unitRef="pure">0.000</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_CD_1_Member"
      decimals="INF"
      id="ixv-32386"
      unitRef="pure">0.004</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_CD_2_Member"
      decimals="INF"
      id="ixv-32387"
      unitRef="pure">0.303</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_CD_3_Member"
      decimals="INF"
      id="ixv-32388"
      unitRef="pure">0.320</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_CD_4_Member"
      decimals="INF"
      id="ixv-32389"
      unitRef="pure">0.181</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_CD_5_Member"
      decimals="INF"
      id="ixv-32390"
      unitRef="pure">0.258</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_CD_6_Member"
      decimals="INF"
      id="ixv-32391"
      unitRef="pure">0.110</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_CD_7_Member"
      decimals="INF"
      id="ixv-32392"
      unitRef="pure">0.000</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_CD_8_Member"
      decimals="INF"
      id="ixv-32393"
      unitRef="pure">0.000</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_CD_9_Member"
      decimals="INF"
      id="ixv-32394"
      unitRef="pure">0.000</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_AA_USGovernmentAgencyMortgageSecurities_Member"
      decimals="INF"
      id="ixv-32395"
      unitRef="pure">0.922</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_AA_CMOsandOtherMortgageRelatedSecurities_Member"
      decimals="INF"
      id="ixv-32396"
      unitRef="pure">0.157</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_AA_USTreasuryObligations_Member"
      decimals="INF"
      id="ixv-32397"
      unitRef="pure">0.097</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_AA_Options_Member"
      decimals="INF"
      id="ixv-32398"
      unitRef="pure">0.002</oef:PctOfNav>
    <oef:LargestHoldingsTableTextBlock contextRef="C000019282_ClassMember" id="ixv-804">TOP HOLDINGS(% of Fund's net assets)

&#160;

&#160;


Ginnie Mae II Pool

66.7


&#160;


Ginnie Mae I Pool

26.2


&#160;


Ginnie Mae REMIC pass-thru certificates

8.0


&#160;


US Treasury Notes

7.4


&#160;


Freddie Mac Multifamily Structured pass-thru certificates

5.6


&#160;


US Treasury Bonds

2.3


&#160;


Fannie Mae Mortgage pass-thru certificates

1.9


&#160;


Freddie Mac Gold Pool

1.0


&#160;


Fannie Mae Guaranteed REMIC

1.0


&#160;


Ginnie Mae Mortgage pass-thru certificates

0.8


&#160;


&#160;

120.9

&#160;



</oef:LargestHoldingsTableTextBlock>
    <oef:PctOfNav
      contextRef="C000019282_TH_0_Member"
      decimals="INF"
      id="ixv-32399"
      unitRef="pure">0.667</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_TH_1_Member"
      decimals="INF"
      id="ixv-32400"
      unitRef="pure">0.262</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_TH_2_Member"
      decimals="INF"
      id="ixv-32401"
      unitRef="pure">0.080</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_TH_3_Member"
      decimals="INF"
      id="ixv-32402"
      unitRef="pure">0.074</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_TH_4_Member"
      decimals="INF"
      id="ixv-32403"
      unitRef="pure">0.056</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_TH_5_Member"
      decimals="INF"
      id="ixv-32404"
      unitRef="pure">0.023</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_TH_6_Member"
      decimals="INF"
      id="ixv-32405"
      unitRef="pure">0.019</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_TH_7_Member"
      decimals="INF"
      id="ixv-32406"
      unitRef="pure">0.010</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_TH_8_Member"
      decimals="INF"
      id="ixv-32407"
      unitRef="pure">0.010</oef:PctOfNav>
    <oef:PctOfNav
      contextRef="C000019282_TH_9_Member"
      decimals="INF"
      id="ixv-32408"
      unitRef="pure">0.008</oef:PctOfNav>
</xbrl>
