Expense Example - FidelityFlexInternationalIndexFund-PRO - FidelityFlexInternationalIndexFund-PRO - Fidelity Flex International Index Fund - Fidelity Flex International Index Fund	Dec. 30, 2024 USD ($)
Expense Example:
1 year	none
3 years	none
5 years	none
10 years	none

No definition available.

Name:	rr_ExpenseExampleAbstract
Namespace Prefix:	rr_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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 N-1A
-Section 3
-Subsection instructions
-Paragraph 4

+ Details

Name:	rr_ExpenseExampleYear01
Namespace Prefix:	rr_
Data Type:	rr:NonNegativeMonetaryType
Balance Type:	na
Period Type:	duration

- Definition

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form N-1A
-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

- Definition

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form N-1A
-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

- Definition

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form N-1A
-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

- Details

Name:	dei_DocumentInformationDocumentAxis=fmr_FidelityFlexInternationalIndexFund-PROMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=fmr_S000056355Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	rr_ProspectusShareClassAxis=fmr_C000177582Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: