| **Expense Example - FidelitySAISustainableInternationalEquityEmergingMarketsEquityFunds-ComboPRO - FidelitySAISustainableInternationalEquityEmergingMarketsEquityFunds-ComboPRO - Fidelity SAI Sustainable Emerging Markets Equity Fund - Fidelity SAI Sustainable Emerging Markets Equity Fund** | Dec. 30, 2023 USD ($) |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------|
| **Expense Example:**                                                                                                                                                                                                                                                                              |                  |
| 1 year                                                                                                                                                                                                                                                                                            | $ 97                  |
| 3 years                                                                                                                                                                                                                                                                                           | 1,005                 |
| 5 years                                                                                                                                                                                                                                                                                           | 2,058                 |
| 10 years                                                                                                                                                                                                                                                                                          | $ 4,690               |

| X                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - References
No definition available.
+ Details**Name:**rr_ExpenseExampleAbstract**Namespace Prefix:**rr_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection instructions -Paragraph 4
+ Details**Name:**rr_ExpenseExampleYear01**Namespace Prefix:**rr_**Data Type:**rr:NonNegativeMonetaryType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 1 -Subparagraph 2
+ Details**Name:**rr_ExpenseExampleYear03**Namespace Prefix:**rr_**Data Type:**rr:NonNegativeMonetaryType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 1 -Subparagraph 2
+ Details**Name:**rr_ExpenseExampleYear05**Namespace Prefix:**rr_**Data Type:**rr:NonNegativeMonetaryType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 3 -Subsection example -Paragraph 1 -Subparagraph 2
+ Details**Name:**rr_ExpenseExampleYear10**Namespace Prefix:**rr_**Data Type:**rr:NonNegativeMonetaryType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**dei_DocumentInformationDocumentAxis=fmr_FidelitySAISustainableInternationalEquityEmergingMarketsEquityFunds-ComboPROMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**dei_LegalEntityAxis=fmr_S000075895Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**rr_ProspectusShareClassAxis=fmr_C000235236Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |