Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	FIDELITY HASTINGS STREET TRUST
12.31 Fidelity Series Emerging Markets Debt Funds Combo PRO-01 | Fidelity Series Emerging Markets Debt Local Currency Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Summary Fund:Fidelity® Series Emerging Markets Debt Local Currency Fund
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The fund seeks high total return.
Expense [Heading]	rr_ExpenseHeading	Fee Table
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder fees
(fees paid directly from your investment)	rr_ShareholderFeeOther	none
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Operating Expenses (expenses that you pay each year as a % of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	April 30, 2024
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	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. For the period from October 30, 2020 to December 31, 2020, the fund's portfolio turnover rate was 17% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	17.00%
Other Expenses, New Fund, Based on Estimates [Text]	rr_OtherExpensesNewFundBasedOnEstimates	Based on estimated amounts for the current fiscal year.
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This example helps compare the cost of investing in the fund with the cost of investing in other funds. 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:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Normally investing at least 80% of the fund’s assets in debt securities of issuers in emerging markets and other debt investments that are tied economically to emerging markets and denominated in the local currency of the issuer. Emerging markets include countries that have an emerging stock market as defined by MSCI, countries or markets with low- to middle-income economies as classified by currency of the World Bank, and other countries or markets with similar emerging characteristics. Emerging markets tend to have relatively low gross national product per capita compared to the world’s major economies and may have the potential for rapid economic growth. Potentially investing in other types of securities, including debt securities of non-emerging market foreign issuers and lower-quality debt securities (those of less than investment-grade quality, also referred to as high yield debt securities or junk bonds) of U.S. issuers. Allocating investments across different emerging market countries. Actively managing the fund’s currency exposures. Utilizing forward foreign currency exchange contracts for both hedging and non-hedging purposes. Analyzing a security's structural features and current pricing, trading opportunities, and the credit, currency, and economic risks of the security and its issuer to select investments.
Risk [Heading]	rr_RiskHeading	Principal Investment Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	Interest Rate Changes. Interest rate increases can cause the price of a debt security to decrease. Foreign and Emerging Market Risk. Foreign markets, particularly emerging markets, can be more volatile than the U.S. market due to increased risks of adverse issuer, political, regulatory, market, or economic developments and can perform differently from the U.S. market. Emerging markets typically have less established legal, accounting and financial reporting systems than those in more developed markets, which may reduce the scope or quality of financial information available to investors. Emerging markets can be subject to greater social, economic, regulatory, and political uncertainties and can be extremely volatile. Foreign exchange rates also can be extremely volatile. Foreign Currency Transactions. The fund may enter into forward foreign currency exchange contracts for both hedging and non-hedging purposes. A forward foreign currency exchange contract, which involves an obligation to purchase or sell a specific currency at a future date at a price set at the time of the contract, reduces a fund’s exposure to changes in the value of the currency it will deliver and increases its exposure to changes in the value of the currency it will receive for the duration of the contract. Foreign exchange rates can be extremely volatile and the degree of volatility of the market or in the direction of the market from that anticipated by the Adviser may result in losses to the fund. Currency Exposure. Because the fund is normally heavily exposed to foreign currencies, it could experience losses based solely on the weakness of foreign currencies versus the U.S. dollar and changes in the exchange rates between foreign currencies and the U.S. dollar. Currency risk may be particularly high to the extent that a fund invests in foreign currencies or engages in foreign currency transactions that are economically tied to emerging market countries. These emerging markets currency transactions may present market, credit, currency, liquidity, legal, political and other risks different from, or greater than, the risks of investing in developed foreign currencies or engaging in foreign currency transactions that are economically tied to developed foreign countries. Issuer-Specific Changes. 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. Lower-quality debt securities (those of less than investment-grade quality, also referred to as high yield debt securities or junk bonds) and certain types of other securities involve greater risk of default or price changes due to changes in the credit quality of the issuer. The value of lower-quality debt securities and certain types of other securities can be more volatile due to increased sensitivity to adverse issuer, political, regulatory, market, or economic developments and can be difficult to resell. In addition, the fund is classified as non-diversified under the Investment Company Act of 1940 (1940 Act), which means that it has the ability to invest a greater portion of assets in securities of a smaller number of individual issuers than a diversified fund. As a result, changes in the market value of a single investment could cause greater fluctuations in share price than would occur in a more diversified fund. 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. You could lose money by investing in the fund.
Risk Lose Money [Text]	rr_RiskLoseMoney	You could lose money by investing in the fund.
Risk Nondiversified Status [Text]	rr_RiskNondiversifiedStatus	In addition, the fund is classified as non-diversified under the Investment Company Act of 1940 (1940 Act), which means that it has the ability to invest a greater portion of assets in securities of a smaller number of individual issuers than a diversified fund. As a result, changes in the market value of a single investment could cause greater fluctuations in share price than would occur in a more diversified fund.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	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.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	Performance history will be available for the fund after the fund has been in operation for one calendar year.
12.31 Fidelity Series Emerging Markets Debt Funds Combo PRO-01 | Fidelity Series Emerging Markets Debt Local Currency Fund | Fidelity Series Emerging Markets Debt Local Currency Fund
Risk/Return:	rr_RiskReturnAbstract
Management fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.12%	[1]
Total annual operating expenses	rr_ExpensesOverAssets	0.12%
Fee waiver and/or expense reimbursement	rr_FeeWaiverOrReimbursementOverAssets	0.12%	[2]
Total annual operating expenses after fee waiver and/or expense reimbursement	rr_NetExpensesOverAssets	none
1 year	rr_ExpenseExampleYear01	none
3 years	rr_ExpenseExampleYear03	none

[1] ^(a)Based on estimated amounts for the current fiscal year.

[2] ^(b)Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse the fund to the extent that total operating expenses (excluding interest, fees and expenses of the Independent Trustees, and acquired fund fees and expenses, if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of its average net assets, exceed 0.003% (the Expense Cap). If at any time during the current fiscal year expenses for the fund fall below the Expense Cap, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Cap. This arrangement will remain in effect through April 30, 2024. FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees and may extend it in its discretion after that date.