2.2.0.25truefalse000901 - Document - Risk/Return Summary {Unlabeled} - (Spartan U.S. Bond Index Fund) (Inst AdvInst)falsefalsetrue1falsefalsetruefalse{dei_DocumentInformationDocumentAxis} : Inst Advinst Member {dei_LegalEntityAxis} : S000017676 Member 4/29/2011 - 4/29/2011 Duration_4_29_2011_To_4_29_2011_dei_DocumentInformationDocumentAxis_cik000035315_InstAdvinstMember_dei_LegalEntityAxis_cik000035315_S000017676Memberhttp://www.sec.gov/CIK0000035315duration2011-04-29T00:00:002011-04-29T00:00:00falsefalsecik000035315_InstAdvinstMemberdei_DocumentInformationDocumentAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_InstAdvinstMemberdei_DocumentInformationDocumentAxisexplicitMemberfalsefalsecik000035315_S000017676Memberdei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_S000017676Memberdei_LegalEntityAxisexplicitMemberUnit1Standardhttp://www.xbrl.org/2003/instancepurexbrli01false0natruenanaNo definition available.falsetruefalsefalsefalsefalsefalsefalsefalsefalsehttp://www.fidelity.com/role/documentriskreturnsummaryunlabeledspartanusbondindexfund1falsefalsefalse00Inst AdvInst | Spartan U.S. Bond Index FundInst AdvInst | Spartan U.S. Bond Index Fundfalsefalsefalsefalsefalse1falsefalsetruefalse{dei_DocumentInformationDocumentAxis} : Inst Advinst Member {dei_LegalEntityAxis} : S000017676 Member 4/29/2011 - 4/29/2011 Duration_4_29_2011_To_4_29_2011_dei_DocumentInformationDocumentAxis_cik000035315_InstAdvinstMember_dei_LegalEntityAxis_cik000035315_S000017676Memberhttp://www.sec.gov/CIK0000035315duration2011-04-29T00:00:002011-04-29T00:00:00falsefalsecik000035315_InstAdvinstMemberdei_DocumentInformationDocumentAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_InstAdvinstMemberdei_DocumentInformationDocumentAxisexplicitMemberfalsefalsecik000035315_S000017676Memberdei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_S000017676Memberdei_LegalEntityAxisexplicitMemberUnit1Standardhttp://www.xbrl.org/2003/instancepurexbrli0OthernaNo definition available.No authoritative reference available.falsefalseInst AdvInst | Spartan U.S. Bond Index Fund3false0rr_RiskReturnHeadingrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div class="MetaData"> <h1 align="left">Fund Summary</h1> <p align="left"><b><a name="ref5299"> </a><a name="fid80644"> </a></b><b>Fund</b>/Class:<br /><b>Spartan</b>^&#174;<b> U.S. Bond Index Fund</b>/Fidelity Advantage^&#174; </p></div>falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringRisk/Return Summary Investment Objectives/Goals Include the following information, in plain English under rule 421(d) under the Securities Act, in the order and subject matter indicatedReference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 2 falsefalseRisk/Return [Heading]4false0rr_ObjectiveHeadingrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div class="MetaData"> <h3 align="left">Investment Objective</h3></div>falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringInvestment Objectives/Goals. Disclose the Fund's investment objectives or goals. A Fund also may identify its type or category (e.g., that it is a Money Market Fund or a balanced fund).Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 2 -Subsection a falsefalseObjective [Heading]5false0rr_ObjectivePrimaryTextBlockrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div> <div class="MetaData"> <p align="left">The fund seeks to provide investment results that correspond to the aggregate price and interest performance of the debt securities in the Barclays Capital^&#174; U.S. Aggregate Bond Index. </p></div> </div>falsefalsefalsefalsefalseOtherus-types:textBlockItemTypestringInvestment Objectives/Goals. Disclose the Fund's investment objectives or goals. A Fund also may identify its type or category (e.g., that it is a Money Market Fund or a balanced fund).Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 2 -Subsection a falsefalseObjective, Primary [Text Block]6false0rr_ExpenseHeadingrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div class="MetaData"> <h3 align="left">Fee Table</h3></div>falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringRisk/Return Summary Fee Table Includes the following information, in plain English under rule 421(d) under the Securities Act, after Item 2 Fees and expenses of the Fund This table describes the fees and expenses that you may pay if you buy and hold shared of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $[_____] in [name of fund family] funds. Shareholder Fees (fees paid directly from your investment) Example This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be You would pay the following expenses if you did not redeem your shares The Example does not reflect sales charges (loads) on reinvested dividends [and other distributions]. If these sales charges (loads) were included, your costs would be higher. Portfolio Turnover The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover may indicate higher transaction costs. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was __% of the average value of its whole portfolio. Instructions. A.3.instructions.6 New Funds. For purposes of this Item, a "New Fund" is a Fund that does not include in Form N-1A financial statements reporting operating results or that includes financial statements for the Fund's initial fiscal year reporting operating results for a period of 6 months or less. The following Instructions apply to New Funds.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 1 -Subparagraph d -Subsection instructions falsefalseExpense [Heading]7false0rr_ExpenseNarrativeTextBlockrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div> <div class="MetaData"> <p align="left">The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.</p></div> </div>falsefalsefalsefalsefalseOtherus-types:textBlockItemTypestringThis table describes the fees and expenses that you may pay if you buy and hold shared of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $[_____] in [name of fund family] funds. Include the narrative explanations in the order indicated. A Fund may modify the narrative explanations if the explanation contains comparable information to that shown.The narrative explanation regarding sales charge discounts is only required by a Fund that offers such discounts and should specify the minimum level of investment required to qualify for a discount. Modify the narrative explanation to state that Fund shares are sold on a national securities exchange at the end of the time periods indicated, and that brokerage commissions for buying and selling Fund shares through a broker are not reflected.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 1 -Subparagraph b -Subsection instructions falsefalseExpense Narrative [Text Block]8false0rr_ShareholderFeesCaptionrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div class="MetaData"><strong>Shareholder fees <font class="_mt" size="-2">(fees paid directly from your investment)</font></strong></div>falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringShareholder Fees (fees paid directly from your investment).Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 1 -Subsection table falsefalseShareholder Fees Caption [Text]9false0rr_ShareholderFeesTableTextBlockrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div> &lt;div style="display:none;" &gt;~ http://www.fidelity.com/role/ScheduleShareholderFeesSpartanUSBondIndexFund column period compact * column dei_DocumentInformationDocumentAxis compact cik000035315_InstAdvinstMember column dei_LegalEntityAxis compact cik000035315_S000017676Member column rr_ProspectusShareClassAxis compact * row primary compact * ~&lt;/div&gt; </div>falsefalse<div> &lt;div style="display:none;" &gt;~ http://www.fidelity.com/role/ScheduleShareholderFeesSpartanUSBondIndexFund column period compact * column dei_DocumentInformationDocumentAxis compact cik000035315_InstAdvinstMember column dei_LegalEntityAxis compact cik000035315_S000017676Member column rr_ProspectusShareClassAxis compact * row primary compact * ~&lt;/div&gt; </div>falsehttp://www.fidelity.com/role/ScheduleShareholderFeesSpartanUSBondIndexFundfalsefalse000902 - Schedule - Shareholder Fees - {Spartan U.S. Bond Index Fund} {Inst AdvInst}truefalsefalse1falseColumnperiodPeriod*Columndei_DocumentInformationDocumentAxisAxiscik000035315_InstAdvinstMemberColumndei_LegalEntityAxisAxiscik000035315_S000017676MemberColumnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*duration2011-04-29T00:00:002011-04-29T00:00:00falsefalseInst AdvInstdei_DocumentInformationDocumentAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_InstAdvinstMemberdei_DocumentInformationDocumentAxisexplicitMemberfalsefalseSpartan U.S. Bond Index Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_S000017676Memberdei_LegalEntityAxisexplicitMemberfalsefalseInstitutional Classrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_C000100042Memberrr_ProspectusShareClassAxisexplicitMemberInst AdvInstSpartan U.S. Bond Index FundInstitutional ClassUnit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170falseUSDfalsefalse$1falseRowprimaryElement*6false0rr_ShareholderFeeOtherrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truefalsetrue1010falsefalsefalsetruefalseMonetaryrr:NonNegativeMonetaryTypemonetaryOther ExpensesReference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 1 -Subparagraph 10 -Subsection table falsefalseAnnual index fund fee (for fund balances under $10,000)0rr_ShareholderFeeOthertruefalsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truefalsetrue1010falsefalsefalsetruefalseOthernanafalsefalseAnnual index fund fee (for fund balances under $10,000)11Shareholder Fees - (USD $)UnKnownUnKnownUnKnownUnKnownfalsetrueColumnperiodPeriod*Columndei_DocumentInformationDocumentAxisAxiscik000035315_InstAdvinstMemberColumndei_LegalEntityAxisAxiscik000035315_S000017676MemberColumnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*RowprimaryElement*falsefalsefalseOtherus-types:textBlockItemTypestringContains a command for the SEC Viewer for the role corresponding to ShareholderFeesData.No authoritative reference available.falsefalseShareholder Fees [Table]10false0rr_OperatingExpensesCaptionrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div class="MetaData"> <p align="left"><b>Annual class operating expenses<br /><font class="_mt" size="-2">(expenses that you pay each year as a % of the value of your investment)</font></b> </p></div>falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringAnnual Fund Operating Expenses (ongoing expenses that you pay each year as a percentage of the value of your investment)Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 1 -Subparagraph 7 -Subsection table falsefalseOperating Expenses Caption [Text]11false0rr_AnnualFundOperatingExpensesTableTextBlockrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div> &lt;div style="display:none;" &gt;~ http://www.fidelity.com/role/ScheduleAnnualFundOperatingExpensesSpartanUSBondIndexFundInstAdvinst1 column period compact * column dei_DocumentInformationDocumentAxis compact cik000035315_InstAdvinstMember column dei_LegalEntityAxis compact cik000035315_S000017676Member column rr_ProspectusShareClassAxis compact * row primary compact * ~&lt;/div&gt; </div>falsefalse<div> &lt;div style="display:none;" &gt;~ http://www.fidelity.com/role/ScheduleAnnualFundOperatingExpensesSpartanUSBondIndexFundInstAdvinst1 column period compact * column dei_DocumentInformationDocumentAxis compact cik000035315_InstAdvinstMember column dei_LegalEntityAxis compact cik000035315_S000017676Member column rr_ProspectusShareClassAxis compact * row primary compact * ~&lt;/div&gt; </div>falsehttp://www.fidelity.com/role/ScheduleAnnualFundOperatingExpensesSpartanUSBondIndexFundInstAdvinst1falsefalse000903 - Schedule - Annual Fund Operating Expenses - {Spartan U.S. Bond Index Fund} {Inst AdvInst}truefalsefalse1falseColumnperiodPeriod*Columndei_DocumentInformationDocumentAxisAxiscik000035315_InstAdvinstMemberColumndei_LegalEntityAxisAxiscik000035315_S000017676MemberColumnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*duration2011-04-29T00:00:002011-04-29T00:00:00falsefalseInst AdvInstdei_DocumentInformationDocumentAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_InstAdvinstMemberdei_DocumentInformationDocumentAxisexplicitMemberfalsefalseSpartan U.S. Bond Index Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_S000017676Memberdei_LegalEntityAxisexplicitMemberfalsefalseInstitutional Classrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_C000100042Memberrr_ProspectusShareClassAxisexplicitMemberInst AdvInstSpartan U.S. Bond Index FundInstitutional ClassUnit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170falseUSDfalsefalse$1falseRowprimaryElement*5false0rr_ManagementFeesOverAssetsrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruetrue0.00050.0005falsefalsefalsetruefalseOtherrr:NonNegativePure4TypepureManagement Fees include investment advisory fees (including any fees based on the Fund's performance), any other management fees payable to the investment adviser or its affiliates, and administrative fees payable to the investment adviser or its affiliates that are not included as "Other Expenses."Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 3 -Subparagraph a -Subsection instructions falsefalseManagement fee0rr_ManagementFeesOverAssetstruefalsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruetrue0.00050.0005falsefalsefalsetruefalseOthernanafalsefalseManagement fee2falseRowprimaryElement*6false0rr_DistributionAndService12b1FeesOverAssetsrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruetrue0.000.00falsefalsefalsetruefalseOtherrr:NonNegativePure4TypepureDistribution [and/or Service] (12b-1) Fees" include all distribution or other expenses incurred during the most recent fiscal year under a plan adopted pursuant to rule 12b-1 [17 CFR 270.12b-1]. Under an appropriate caption or a subcaption of "Other Expenses," disclose the amount of any distribution or similar expenses deducted from the Fund's assets other than pursuant to a rule 12b-1 plan.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 1 -Subparagraph 9 -Subsection table falsefalseDistribution and/or Service (12b-1) fees0rr_DistributionAndService12b1FeesOverAssetstruefalsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruetrue0.000.00falsefalsefalsetruefalseOthernanafalsefalseDistribution and/or Service (12b-1) fees3falseRowprimaryElement*7false0rr_OtherExpensesOverAssetsrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruetrue0.00120.0012falsefalsefalsetruefalseOtherrr:NonNegativePure4Typepure"Other Expenses" include all expenses not otherwise disclosed in the table that are deducted from the Fund's assets or charged to all shareholder accounts. The amount of expenses deducted from the Fund's assets are the amounts shown as expenses in the Fund's statement of operations (including increases resulting from complying with paragraph 2(g) of rule 6-07 of Regulation S-X [17 CFR 210.6-07]). "Other Expenses" do not include extraordinary expenses as determined under generally accepted accounting principles (see Accounting Principles Board Opinion No. 30). If extraordinary expenses were incurred that materially affected the Fund's "Other Expenses," disclose in a footnote to the table what "Other Expenses" would have been had the extraordinary expenses been included.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 3 -Subparagraph c -Clause i -Subsection instructions falsefalseOther expenses0rr_OtherExpensesOverAssetstruefalsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruetrue0.00120.0012falsefalsefalsetruefalseOthernanafalsefalseOther expenses4falseRowprimaryElement*8false0rr_ExpensesOverAssetsrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalsetotallabel1truetruetrue0.00170.0017falsefalsefalsetruefalseOtherrr:NonNegativePure4TypepureTotal Annual Fund Operating Expenses. If the Fund is a Feeder Fund, reflect the aggregate expenses of the Feeder Fund and the Master Fund in a single fee table using the captions provided. In a footnote to the fee table, state that the table and Example reflect the expenses of both the Feeder and Master Funds. If the prospectus offers more than one Class of a Multiple Class Fund or more than one Feeder Fund that invests in the same Master Fund, provide a separate response for each Class or Feeder Fund. Base the percentages of "Annual Fund Operating Expenses" on amounts incurred during the Fund's most recent fiscal year, but include in expenses amounts that would have been incurred absent expense reimbursement or fee waiver arrangements. If the Fund has changed its fiscal year and, as a result, the most recent fiscal year is less than three months, use the fiscal year prior to the most recent fiscal year as the basis for determining "Annual Fund Operating Expenses."Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 3 -Subparagraph d -Subsection instructions truefalseTotal annual operating expenses0rr_ExpensesOverAssetstruefalsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruetrue0.00170.0017falsefalsefalsetruefalseOthernanafalsefalseTotal annual operating expenses14Annual Fund Operating Expenses - UnKnownUnKnownUnKnownUnKnownfalsetrueColumnperiodPeriod*Columndei_DocumentInformationDocumentAxisAxiscik000035315_InstAdvinstMemberColumndei_LegalEntityAxisAxiscik000035315_S000017676MemberColumnrr_ProspectusShareClassAxisAxis*ColumnunitUnit*RowprimaryElement*falsefalsefalseOtherus-types:textBlockItemTypestringContains a command for the SEC Viewer for the role corresponding to OperatingExpensesData.No authoritative reference available.falsefalseAnnual Fund Operating Expenses [Table]12false0rr_ExpenseExampleNarrativeTextBlockrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div> <div class="MetaData"> <p align="left">This <b>example</b> helps compare the cost of investing in the fund with the cost of investing in other mutual funds. </p> <p align="left">Let's say, hypothetically, that the annual return for shares of the fund is 5% and that your shareholder fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated: </p></div> </div>falsefalsefalsefalsefalseOtherus-types:textBlockItemTypestringThe Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 1 -Subparagraph 1 -Subsection example falsefalseExpense Example Narrative [Text Block]13false0rr_ExpenseExampleWithRedemptionTableTextBlockrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div> &lt;div style="display:none;" &gt;~ http://www.fidelity.com/role/ScheduleExpenseExampleTransposedSpartanUSBondIndexFund row period compact * row dei_DocumentInformationDocumentAxis compact cik000035315_InstAdvinstMember row dei_LegalEntityAxis compact cik000035315_S000017676Member row rr_ProspectusShareClassAxis compact * column primary compact * ~&lt;/div&gt; </div>falsefalse<div> &lt;div style="display:none;" &gt;~ http://www.fidelity.com/role/ScheduleExpenseExampleTransposedSpartanUSBondIndexFund row period compact * row dei_DocumentInformationDocumentAxis compact cik000035315_InstAdvinstMember row dei_LegalEntityAxis compact cik000035315_S000017676Member row rr_ProspectusShareClassAxis compact * column primary compact * ~&lt;/div&gt; </div>truehttp://www.fidelity.com/role/ScheduleExpenseExampleTransposedSpartanUSBondIndexFundfalsefalse000904 - Schedule - Expense Example {Transposed} - {Spartan U.S. Bond Index Fund} {Inst AdvInst}truefalsefalse1falseColumnperiodPeriod*Columndei_DocumentInformationDocumentAxisAxiscik000035315_InstAdvinstMemberColumndei_LegalEntityAxisAxiscik000035315_S000017676MemberColumnrr_ProspectusShareClassAxisAxis*duration2011-04-29T00:00:002011-04-29T00:00:00falsefalseInst AdvInstdei_DocumentInformationDocumentAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_InstAdvinstMemberdei_DocumentInformationDocumentAxisexplicitMemberfalsefalseSpartan U.S. Bond Index Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_S000017676Memberdei_LegalEntityAxisexplicitMemberfalsefalseInstitutional Classrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_C000100042Memberrr_ProspectusShareClassAxisexplicitMemberInst AdvInstSpartan U.S. Bond Index FundInstitutional ClassfalseUSDfalsefalse$1falseRowprimaryElement*RowunitUnit*5false0rr_ExpenseExampleYear01rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truefalsetrue1717falsefalsefalsetruefalseMonetaryrr:NonNegativeMonetaryTypemonetaryThe Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 4 -Subsection instructions falsefalse1 yearUnit12Standardhttp://www.xbrl.org/2003/iso4217USDiso421700rr_ExpenseExampleYear01truefalsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truefalsetrue1717falsefalsefalsetruefalseOthernanafalsefalse1 year2falseRowprimaryElement*RowunitUnit*6false0rr_ExpenseExampleYear03rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truefalsetrue5555falsefalsefalsetruefalseMonetaryrr:NonNegativeMonetaryTypemonetaryThe Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 1 -Subparagraph 2 -Subsection example falsefalse3 yearsUnit12Standardhttp://www.xbrl.org/2003/iso4217USDiso421700rr_ExpenseExampleYear03truefalsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truefalsetrue5555falsefalsefalsetruefalseOthernanafalsefalse3 years3falseRowprimaryElement*RowunitUnit*7false0rr_ExpenseExampleYear05rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truefalsetrue9696falsefalsefalsetruefalseMonetaryrr:NonNegativeMonetaryTypemonetaryThe Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 1 -Subparagraph 2 -Subsection example falsefalse5 yearsUnit12Standardhttp://www.xbrl.org/2003/iso4217USDiso421700rr_ExpenseExampleYear05truefalsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truefalsetrue9696falsefalsefalsetruefalseOthernanafalsefalse5 years4falseRowprimaryElement*RowunitUnit*8false0rr_ExpenseExampleYear10rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truefalsetrue217217falsefalsefalsetruefalseMonetaryrr:NonNegativeMonetaryTypemonetaryThe Example assumes that you invest $10,000 in the Fund for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 1 -Subparagraph 2 -Subsection example falsefalse10 yearsUnit12Standardhttp://www.xbrl.org/2003/iso4217USDiso421700rr_ExpenseExampleYear10truefalsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truefalsetrue217217falsefalsefalsetruefalseOthernanafalsefalse10 years14Expense Example - (USD $)UnKnownUnKnownUnKnownUnKnownfalsetrueColumnperiodPeriod*Columndei_DocumentInformationDocumentAxisAxiscik000035315_InstAdvinstMemberColumndei_LegalEntityAxisAxiscik000035315_S000017676MemberColumnrr_ProspectusShareClassAxisAxis*RowprimaryElement*RowunitUnit*falsefalsefalseOtherus-types:textBlockItemTypestringContains a command for the SEC Viewer for the role corresponding to ExpenseExample.No authoritative reference available.falsefalseExpense Example, With Redemption [Table]14false0rr_PortfolioTurnoverHeadingrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div class="MetaData"> <h3 align="left">Portfolio Turnover</h3></div>falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringDisclose the portfolio turnover rate provided in response to Item 14(a) for the most recent fiscal year (or for such shorter period as the Fund has been in operation). Disclose the period for which the information is provided if less than a full fiscal year. A Fund that is a Money Market Fund may omit the portfolio turnover information required by this Item.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 5 -Subsection instructions falsefalsePortfolio Turnover [Heading]15false0rr_PortfolioTurnoverTextBlockrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div> <div class="MetaData"> <p align="left">The fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual operating expenses or in the example, affect the fund's performance. During the most recent fiscal year, the fund's portfolio turnover rate was&nbsp;<font class="_mt">165%</font> of the average value of its portfolio. </p></div> </div>falsefalsefalsefalsefalseOtherus-types:textBlockItemTypestringDisclose the portfolio turnover rate provided in response to Item 14(a) for the most recent fiscal year (or for such shorter period as the Fund has been in operation). Disclose the period for which the information is provided if less than a full fiscal year. A Fund that is a Money Market Fund may omit the portfolio turnover information required by this Item.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Paragraph 3 -Subsection example falsefalsePortfolio Turnover [Text Block]16false0rr_StrategyHeadingrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div class="MetaData"> <h3 align="left">Principal Investment Strategies</h3></div>falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringPrincipal investment strategies of the Fund. Summarize how the Fund intends to achieve its investment objectives by identifying the Fund's principal investment strategies (including the type or types of securities in which the Fund invests or will invest principally) and any policy to concentrate in securities of issuers in a particular industry or group of industries.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection a falsefalseStrategy [Heading]17false0rr_StrategyNarrativeTextBlockrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div> <div class="MetaData"> <ul> <li>Normally investing at least 80% of the fund's assets in bonds included in the Barclays Capital^&#174; U.S. Aggregate Bond Index (the Index). </li> <li>Using statistical sampling techniques based on duration, maturity, interest rate sensitivity, security structure, and credit quality to attempt to replicate the returns of the Index using a smaller number of securities. </li> <li>Engaging in transactions that have a leveraging effect on the fund, including investments in derivatives - such as swaps (interest rate, total return, and credit default) and futures contracts - and forward-settling securities, to adjust the fund's risk exposure. </li> <li>Investing in Fidelity's central funds (specialized investment vehicles used by Fidelity funds to invest in particular security types or investment disciplines).</li></ul></div> </div>falsefalsefalsefalsefalseOtherus-types:textBlockItemTypestringPrincipal investment strategies of the Fund. Summarize how the Fund intends to achieve its investment objectives by identifying the Fund's principal investment strategies (including the type or types of securities in which the Fund invests or will invest principally) and any policy to concentrate in securities of issuers in a particular industry or group of industries.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Subsection a falsefalseStrategy Narrative [Text Block]18false0rr_RiskHeadingrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div class="MetaData"> <h3 align="left"><a name="ref5317"><font class="_mt">Principal Investment Risks</font></a></h3></div>falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringNarrative Risk Disclosure.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 1 -Subsection b falsefalseRisk [Heading]19false0rr_RiskNarrativeTextBlockrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div> <div class="MetaData"> <ul> <li><i>Interest Rate Changes.</i> Interest rate increases can cause the price of a debt security to decrease. </li> <li><i>Foreign Exposure.</i> Entities located in foreign countries can be affected by adverse political, regulatory, market, or&nbsp;economic developments in those countries. </li> <li><i>Prepayment.</i> The ability of an issuer of a debt security to repay principal prior to a security's maturity can cause greater price volatility if interest rates change. </li> <li><i>Issuer-Specific Changes.</i> The value of an individual security or particular type of security can be more volatile than, and can perform differently from, the market as a whole. A decline in the credit quality of an issuer or a provider&nbsp;of credit support or a maturity-shortening structure for a security can&nbsp;cause the price of a security to decrease. </li> <li><i>Leverage Risk.</i> Leverage can increase market exposure, magnify investment risks, and cause losses to be realized more quickly. </li></ul> <p align="left"><font class="_mt">An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.</font>Unlike individual debt securities, which typically pay principal at maturity, the value of an investment in the fund will fluctuate. <font class="_mt">You could lose money by investing in the fund.</font></p></div> </div>falsefalsefalsefalsefalseOtherus-types:textBlockItemTypestringNarrative Risk Disclosure. A Fund may, in responding to this Item, describe the types of investors for whom the Fund is intended or the types of investment goals that may be consistent with an investment in the Fund.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 1 -Subparagraph i -Clause instruction -Subsection b falsefalseRisk Narrative [Text Block]20false0rr_BarChartAndPerformanceTableHeadingrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div class="MetaData"> <h3 align="left">Performance</h3></div>falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringRisk/Return Bar Chart and Table.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subsection b falsefalseBar Chart and Performance Table [Heading]21false0rr_PerformanceNarrativeTextBlockrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div> <div class="MetaData"> <p align="left">The following information is intended to help you understand the risks of investing in the fund.&nbsp;<font class="_mt">The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index over various periods of time.</font> The index description appears in the Additional Information about the Index section of the prospectus.&nbsp;<font class="_mt">Past performance (before and after taxes) is not an indication of future performance.</font> </p> <div> <p align="left">Visit&nbsp;<font class="_mt">www.fidelity.com</font> for updated return information. </p> <p align="left"><font class="_mt">Performance history will be available for Fidelity Advantage Class after Fidelity Advantage Class has been in operation for one calendar year.</font></p></div></div> </div>falsefalsefalsefalsefalseOtherus-types:textBlockItemTypestringRisk/Return Bar Chart and Table.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subsection b falsefalsePerformance Narrative [Text Block]22false0rr_BarChartHeadingrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div class="MetaData"> <div><font class="_mt" size="-1"> </font> <div> <div> <p style="line-height: normal; margin: 0in 0in 10pt;" class="MsoNormal"><font style="font-family: 'Times New Roman','serif'; color: black; font-size: 13.5pt;" class="_mt"><strong>Year-by-Year Returns</strong></font>^{<font style="font-family: 'Times New Roman','serif'; color: black; font-size: 10pt;" class="_mt">[1]</font>}</p> <p style="line-height: normal; margin: 0in 0in 10pt;" class="MsoNormal">&nbsp;</p></div></div><font class="_mt" size="1"><font class="_mt"><font style="line-height: 115%; font-family: 'Times New Roman','serif'; font-size: 7.5pt;" class="_mt">Calendar Years</font></font></font> <p>&nbsp;</p> <p style="margin-top: 0px; margin-bottom: 0px;" align="left"><font class="_mt" size="1"><font class="_mt"> </font></font></p></div></div>falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringRisk/Return Bar Chart and Table.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subsection b falsefalseBar Chart [Heading]23false0rr_BarChartTableTextBlockrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div> &lt;div style="display:none;" &gt;~ http://www.fidelity.com/role/ScheduleAnnualTotalReturnsSpartanUSBondIndexFundInstAdvinstBarChart column period compact * column primary compact * row dei_DocumentInformationDocumentAxis compact cik000035315_InstAdvinstMember row dei_LegalEntityAxis compact cik000035315_S000017676Member row rr_ProspectusShareClassAxis compact * ~&lt;/div&gt; </div>falsefalseBarChart1.jpg<div> &lt;div style="display:none;" &gt;~ http://www.fidelity.com/role/ScheduleAnnualTotalReturnsSpartanUSBondIndexFundInstAdvinstBarChart column period compact * column primary compact * row dei_DocumentInformationDocumentAxis compact cik000035315_InstAdvinstMember row dei_LegalEntityAxis compact cik000035315_S000017676Member row rr_ProspectusShareClassAxis compact * ~&lt;/div&gt; </div>falsehttp://www.fidelity.com/role/ScheduleAnnualTotalReturnsSpartanUSBondIndexFundInstAdvinstBarChartfalsefalse000906 - Schedule - Annual Total Returns - {Spartan U.S. Bond Index Fund} {Inst AdvInst}truefalsefalse1falseColumnperiodPeriod*ColumnprimaryElement*ColumnunitUnit*5false0rr_AnnualReturn2001rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.08080.0808[1]falsefalsefalsetruefalseOtherxbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph ii -Subsection b falsefalseAnnual Return 2001duration2011-04-29T00:00:002011-04-29T00:00:00Standard0falseUSDfalsefalse$2falseColumnperiodPeriod*ColumnprimaryElement*ColumnunitUnit*6false0rr_AnnualReturn2002rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.10220.1022[1]falsefalsefalsetruefalseOtherxbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph ii -Subsection b falsefalseAnnual Return 2002duration2011-04-29T00:00:002011-04-29T00:00:00Standard0falseUSDfalsefalse$3falseColumnperiodPeriod*ColumnprimaryElement*ColumnunitUnit*7false0rr_AnnualReturn2003rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.04910.0491[1]falsefalsefalsetruefalseOtherxbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a -Subsection b falsefalseAnnual Return 2003duration2011-04-29T00:00:002011-04-29T00:00:00Standard0falseUSDfalsefalse$4falseColumnperiodPeriod*ColumnprimaryElement*ColumnunitUnit*8false0rr_AnnualReturn2004rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.04360.0436[1]falsefalsefalsetruefalseOtherxbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a -Subsection b falsefalseAnnual Return 2004duration2011-04-29T00:00:002011-04-29T00:00:00Standard0falseUSDfalsefalse$5falseColumnperiodPeriod*ColumnprimaryElement*ColumnunitUnit*9false0rr_AnnualReturn2005rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.02260.0226[1]falsefalsefalsetruefalseOtherxbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph ii -Subsection b falsefalseAnnual Return 2005duration2011-04-29T00:00:002011-04-29T00:00:00Standard0falseUSDfalsefalse$6falseColumnperiodPeriod*ColumnprimaryElement*ColumnunitUnit*10false0rr_AnnualReturn2006rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.04330.0433[1]falsefalsefalsetruefalseOtherxbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph ii -Subsection b falsefalseAnnual Return 2006duration2011-04-29T00:00:002011-04-29T00:00:00Standard0falseUSDfalsefalse$7falseColumnperiodPeriod*ColumnprimaryElement*ColumnunitUnit*11false0rr_AnnualReturn2007rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.05400.0540[1]falsefalsefalsetruefalseOtherxbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a -Subsection b falsefalseAnnual Return 2007duration2011-04-29T00:00:002011-04-29T00:00:00Standard0falseUSDfalsefalse$8falseColumnperiodPeriod*ColumnprimaryElement*ColumnunitUnit*12false0rr_AnnualReturn2008rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.03760.0376[1]falsefalsefalsetruefalseOtherxbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph ii -Subsection b falsefalseAnnual Return 2008duration2011-04-29T00:00:002011-04-29T00:00:00Standard0falseUSDfalsefalse$9falseColumnperiodPeriod*ColumnprimaryElement*ColumnunitUnit*13false0rr_AnnualReturn2009rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.06450.0645[1]falsefalsefalsetruefalseOtherxbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit a -Subsection b falsefalseAnnual Return 2009duration2011-04-29T00:00:002011-04-29T00:00:00Standard0falseUSDfalsefalse$10falseColumnperiodPeriod*ColumnprimaryElement*ColumnunitUnit*14false0rr_AnnualReturn2010rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruefalse0.06290.0629[1]falsefalsefalsetruefalseOtherxbrli:pureItemTypepureIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph ii -Subsection b falsefalseAnnual Return 2010duration2011-04-29T00:00:002011-04-29T00:00:00Standard0falseUSDfalsefalse$1falseRowdei_DocumentInformationDocumentAxisAxiscik000035315_InstAdvinstMemberRowdei_LegalEntityAxisAxiscik000035315_S000017676MemberRowrr_ProspectusShareClassAxisAxis*falsefalseInst AdvInstdei_DocumentInformationDocumentAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_InstAdvinstMemberdei_DocumentInformationDocumentAxisexplicitMemberfalsefalseSpartan U.S. Bond Index Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_S000017676Memberdei_LegalEntityAxisexplicitMemberfalsefalseInvestor Classrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_C000048843Memberrr_ProspectusShareClassAxisexplicitMemberInst AdvInstSpartan U.S. Bond Index FundInvestor Class0truefalsefalsefalsefalsefalsefalsefalsefalsefalsefalse[1]1truetruefalse0.08080.0808falsefalsefalsetruefalse2truetruefalse0.10220.1022falsefalsefalsetruefalse3truetruefalse0.04910.0491falsefalsefalsetruefalse4truetruefalse0.04360.0436falsefalsefalsetruefalse5truetruefalse0.02260.0226falsefalsefalsetruefalse6truetruefalse0.04330.0433falsefalsefalsetruefalse7truetruefalse0.05400.0540falsefalsefalsetruefalse8truetruefalse0.03760.0376falsefalsefalsetruefalse9truetruefalse0.06450.0645falsefalsefalsetruefalse10truetruefalse0.06290.0629falsefalsefalsetruefalseOthernanafalsefalseInst AdvInst Spartan U.S. Bond Index Fund Investor Class1The returns shown above are for Investor Class, a class of shares of the fund that is not offered through this prospectus. Fidelity Advantage Class would have substantially similar annual returns to Investor Class because the classes are invested in the same portfolio of securities. Fidelity Advantage Class's returns would differ from Investor Class's returns to the extent that the classes do not have the same expenses.101Annual Total Returns - UnKnownUnKnownUnKnownUnKnownfalsetrueColumnperiodPeriod*ColumnprimaryElement*ColumnunitUnit*Rowdei_DocumentInformationDocumentAxisAxiscik000035315_InstAdvinstMemberRowdei_LegalEntityAxisAxiscik000035315_S000017676MemberRowrr_ProspectusShareClassAxisAxis*falsefalsefalseOtherus-types:textBlockItemTypestringContains a command for the SEC Viewer for the role corresponding to BarChartData.No authoritative reference available.falsefalseBar Chart [Table]24false0rr_BarChartClosingTextBlockrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div> <div class="MetaData"> <table border="1" width="95%"> <tr><td valign="bottom" align="left"> <p align="left"><i><font class="_mt" size="-1">During the periods shown in the chart:</font></i> </p></td> <td valign="bottom" align="center"> <p align="center"><i><font class="_mt" size="-2">Returns</font></i> </p></td> <td valign="bottom" align="center"> <p align="center"><i><font class="_mt" size="-2">Quarter ended</font></i> </p></td></tr> <tr><td valign="bottom" align="left"> <p align="left"><i><font class="_mt" size="-1">Highest Quarter Return</font></i> </p></td> <td valign="bottom" align="left"> <p align="right"><i><font class="_mt" size="-1">4.86%</font></i> </p></td> <td valign="bottom" align="left"> <p align="left"><i><font class="_mt" size="-1">September 30, 2001</font></i> </p></td></tr> <tr><td valign="bottom" align="left"> <p align="left"><i><font class="_mt" size="-1">Lowest Quarter Return</font></i> </p></td> <td valign="bottom" align="left"> <p align="right"><i><font class="_mt" size="-1">-2.56%</font></i> </p></td> <td valign="bottom" align="left"> <p align="left"><i><font class="_mt" size="-1">June 30, 2004</font></i> </p></td></tr> <tr><td valign="bottom" align="left"> <p align="left"><i><font class="_mt" size="-1">Year to Date Return</font></i> </p></td> <td valign="bottom" align="left"> <p align="right"><i><font class="_mt" size="-1">0.30%</font></i> </p></td> <td valign="bottom" align="left"> <p align="left"><i><font class="_mt" size="-1">March 31, 2011</font></i> </p></td></tr></table></div> </div>falsefalsefalsefalsefalseOtherus-types:textBlockItemTypestringIf the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph ii -Subsection b falsefalseBar Chart Closing [Text Block]25false0rr_PerformanceTableHeadingrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div class="MetaData"> <h3 align="left">Average Annual Returns </h3></div>falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringThis item represents Average Anuual Total Returns. If a Multiple Class Fund offers a Class in the prospectus that converts into another Class after a stated period, compute average annual total returns in the table by using the returns of the other Class for the period after conversion.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph instructions -Clause 3 -Exhibit c -Subsection b falsefalsePerformance Table Heading26false0rr_PerformanceTableNarrativeTextBlockrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div> <div class="MetaData"> <div> <p style="margin-top: 0px; margin-bottom: 0px;" align="left"><font class="_mt">After-tax returns are calculated using the historical highest individual federal marginal income tax rates, but do not reflect the impact of state or local taxes.&nbsp; </font><font class="_mt">Actual after-tax returns may differ depending on your individual circumstances.&nbsp;<font class="_mt">The after-tax returns shown are not relevant if you hold your shares in a retirement account or in another tax-deferred arrangement.</font></font>&nbsp;<font class="_mt">Return After Taxes on Distributions and Sale of Fund Shares may be higher than other returns for the same period due to a tax benefit of realizing a capital loss upon the sale of fund shares.</font> </p></div> <p style="margin-top: 0px; margin-bottom: 0px;" align="left">&nbsp;</p> <p style="margin-top: 0px; margin-bottom: 0px;" align="left"><font class="_mt" size="-2">For the periods ended<br />December 31, 2010</font></p></div> </div>falsefalsefalsefalsefalseOtherus-types:textBlockItemTypestringIf the Fund has annual returns for at least one calendar year, provide a table showing the Fund's (A) average annual total return; (B) average annual total return (after taxes on distributions); and (C) average annual total return (after taxes on distributions and redemption). A Money Market Fund should show only the returns described in clause (A) of the preceding sentence. All returns should be shown for 1-, 5-, and 10- calendar year periods ending on the date of the most recently completed calendar year (or for the life of the Fund, if shorter), but only for periods subsequent to the effective date of the Fund's registration statement. The table also shouldshow the returns of an appropriate broadbased securities market index as defined in Instruction 5 to Item 22(b)(7) for the same periods. A Fund that has been in existence for more than 10 years also may include returns for the life of the Fund. A Money Market Fund may provide the Fund's 7-day yield ending on the date of the most recent calendar year or disclose a toll-free (or collect) telephone number that investors can use to obtain the Fund's current 7-day yield. For a Fund (other than a Money Market Fund or a Fund described in General Instruction C.3.(d)(iii)), provide the information in the following table with the specified captions AVERAGE ANNUAL TOTAL RETURNS (For the periods ended December 31, _____). For a Fund that provides annual total returns for only one calendar year or for a Fund that does not include the bar chart because it does not have annual returns for a full calendar year, modify, as appropriate, the narrative explanation required by paragraph (c)(2)(i) (e.g., by stating that the information gives some indication of the risks of an investment in the Fund by comparing the Fund's performance with a broad measure of market performance).Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph iv -Subsection b falsefalsePerformance Table Narrative27false0rr_PerformanceTableTextBlockrrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00<div> &lt;div style="display:none;" &gt;~ http://www.fidelity.com/role/ScheduleAverageAnnualTotalReturnsTransposedSpartanUSBondIndexFund row period compact * row primary compact * column dei_DocumentInformationDocumentAxis compact 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available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truetruetrue0.06290.0629[1]falsefalsefalsetruefalse2truetruetrue0.05060.0506[1]falsefalsefalsetruefalse3truetruetrue0.04220.0422[1]falsefalsefalsetruefalse4truetruetrue0.06540.0654falsefalsefalsetruefalseOtherxbrli:pureItemTypepureReturn Before Taxes.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 -Subsection b falsefalsePast 1 yearduration2011-04-29T00:00:002011-04-29T00:00:00falseUSDfalsefalse$2falseColumnperiodPeriod*ColumnprimaryElement*6false0rr_AverageAnnualReturnYear05rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truetruetrue0.05240.0524[1]falsefalsefalsetruefalse2truetruetrue0.03680.0368[1]falsefalsefalsetruefalse3truetruetrue0.03570.0357[1]falsefalsefalsetruefalse4truetruetrue0.05800.0580falsefalsefalsetruefalseOtherxbrli:pureItemTypepureReturn Before Taxes.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 -Subsection b falsefalsePast 5 yearsduration2011-04-29T00:00:002011-04-29T00:00:00falseUSDfalsefalse$3falseColumnperiodPeriod*ColumnprimaryElement*7false0rr_AverageAnnualReturnYear10rrfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truetruetrue0.05580.0558[1]falsefalsefalsetruefalse2truetruetrue0.03850.0385[1]falsefalsefalsetruefalse3truetruetrue0.03760.0376[1]falsefalsefalsetruefalse4truetruetrue0.05840.0584falsefalsefalsetruefalseOtherxbrli:pureItemTypepureReturn Before Taxes.Reference 1: 1 -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 4 -Paragraph 2 -Subparagraph iii -Clause 1 -Exhibit 2 -Subsection b falsefalsePast 10 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Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_S000017676Memberdei_LegalEntityAxisexplicitMemberfalsefalseInvestor Classrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_C000048843Memberrr_ProspectusShareClassAxisexplicitMemberfalsefalseReturn After Taxes on Distributions and Sale of Fund Sharesrr_PerformanceMeasureAxisxbrldihttp://xbrl.org/2006/xbrldirr_AfterTaxesOnDistributionsAndSalesMemberrr_PerformanceMeasureAxisexplicitMemberInst AdvInstSpartan U.S. Bond Index FundInvestor ClassReturn After Taxes on Distributions and Sale of Fund SharesStandard00truefalsefalsefalsefalsefalsefalsefalsefalsefalsefalse[1]1truetruetrue0.04220.0422falsefalsefalsetruefalse2truetruetrue0.03570.0357falsefalsefalsetruefalse3truetruetrue0.03760.0376falsefalsefalsetruefalseOthernanafalsefalseInvestor Class Return After Taxes on Distributions and Sale of Fund Shares4falseRowdei_DocumentInformationDocumentAxisAxiscik000035315_InstAdvinstMemberRowdei_LegalEntityAxisAxiscik000035315_S000017676MemberRowrr_ProspectusShareClassAxisAxis*Rowrr_PerformanceMeasureAxisAxis*RowunitUnit*falsefalseInst AdvInstdei_DocumentInformationDocumentAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_InstAdvinstMemberdei_DocumentInformationDocumentAxisexplicitMemberfalsefalseSpartan U.S. Bond Index Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_S000017676Memberdei_LegalEntityAxisexplicitMembertruefalseShare Classesrr_ProspectusShareClassAxisrr_ShareClassDomainrr_ProspectusShareClassAxisexplicitMemberfalsefalseBarclays Capital U.S. Aggregate Bond Index (reflects no deduction for fees, expenses, or taxes)rr_PerformanceMeasureAxisxbrldihttp://xbrl.org/2006/xbrldicik000035315_BarclaysCapitalUSAggregateBondIndexMemberrr_PerformanceMeasureAxisexplicitMemberInst AdvInstSpartan U.S. Bond Index FundShare ClassesBarclays Capital U.S. Aggregate Bond Index (reflects no deduction for fees, expenses, or taxes)Standard00truefalsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruetrue0.06540.0654falsefalsefalsetruefalse2truetruetrue0.05800.0580falsefalsefalsetruefalse3truetruetrue0.05840.0584falsefalsefalsetruefalseOthernanafalsefalseBarclays Capital U.S. Aggregate Bond Index (reflects no deduction for fees, expenses, or taxes)1The returns shown above are for Investor Class, a class of shares of the fund that is not offered through this prospectus. Fidelity Advantage Class would have substantially similar annual returns to Investor Class because the classes are invested in the same portfolio of securities. Fidelity Advantage Class's returns would differ from Investor Class's returns to the extent that the classes do not have the same expenses. 34Average Annual Total Returns - Inst AdvInst Spartan U.S. Bond Index FundUnKnownUnKnownUnKnownUnKnownfalsetrueColumnperiodPeriod*ColumnprimaryElement*Rowdei_DocumentInformationDocumentAxisAxiscik000035315_InstAdvinstMemberRowdei_LegalEntityAxisAxiscik000035315_S000017676MemberRowrr_ProspectusShareClassAxisAxis*Rowrr_PerformanceMeasureAxisAxis*RowunitUnit*falsefalsefalseOtherus-types:textBlockItemTypestringContains a command for the SEC Viewer for the role corresponding to PerformanceTableData.No authoritative reference available.falsefalsePerformance [Table]126Risk/Return Summary - (Spartan U.S. Bond Index Fund) (Inst AdvInst) (Inst AdvInst, Spartan U.S. Bond Index Fund)UnKnownUnKnownUnKnownUnKnownfalsetrue