Shareholder Fees {- Fidelity SAI U.S. Value Index Fund}	Sep. 29, 2020 USD ($)
07.31 Fidelity SAI U.S. Value Index Fund PRO-06 \| Fidelity SAI U.S. Value Index Fund
Shareholder Fees:
(fees paid directly from your investment)	none

Other Expenses

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 3
-Subsection table
-Paragraph 1
-Subparagraph 10

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