Risk/Return Detail Data - FidelitySAIRealEstateFund-PRO	Jul. 10, 2024 USD ($)
Risk/Return:
Registrant Name	Fidelity Summer Street Trust
FidelitySAIRealEstateFund-PRO | Fidelity SAI Real Estate Fund
Risk/Return:
Risk/Return [Heading]	Fund Summary Fund: Fidelity® SAI Real Estate Fund
Objective [Heading]	Investment Objective
Objective, Primary [Text Block]	Fidelity® SAI Real Estate Fund seeks above-average income and long-term capital growth, consistent with reasonable investment risk. The fund seeks to provide a yield that exceeds the composite yield of the S&P 500 ® Index.
Expense [Heading]	Fee Table
Expense Narrative [Text Block]	The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund.
Shareholder Fees Caption [Text]	Shareholder fees
(fees paid directly from your investment)	none
Operating Expenses Caption [Text]	Annual Operating Expenses
Portfolio Turnover [Heading]	Portfolio Turnover
Portfolio Turnover [Text Block]	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.
Other Expenses, New Fund, Based on Estimates [Text]	Based on estimated amounts for the current fiscal year.
Expense Example Narrative [Text Block]	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 the 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]	Principal Investment Strategies
Strategy Narrative [Text Block]	Normally investing primarily in common stocks. Normally investing at least 80% of assets in securities of companies principally engaged in the real estate industry and other real estate related investments. Investing in domestic and foreign issuers. Using fundamental analysis of factors such as each issuer's financial condition and industry position, as well as market and economic conditions, to select investments.
Strategy Portfolio Concentration [Text]	Normally investing at least 80% of assets in securities of companies principally engaged in the real estate industry and other real estate related investments.
Risk [Heading]	Principal Investment Risks
Bar Chart and Performance Table [Heading]	Performance
Performance Narrative [Text Block]	Performance history will be available for the fund after the fund has been in operation for one calendar year.
Performance One Year or Less [Text]	Performance history will be available for the fund after the fund has been in operation for one calendar year.
FidelitySAIRealEstateFund-PRO | Fidelity SAI Real Estate Fund | Fidelity SAI Real Estate Fund
Risk/Return:
Management fee	0.50%
Distribution and/or Service (12b-1) fees	none
Other expenses	0.06%	[1]
Total annual operating expenses	0.56%
1 year	$ 57
3 years	$ 179

[1] A Based on estimated amounts for the current fiscal year.