Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

State Street Institutional Investment Trust

Prospectus Date

rr_ProspectusDate

May 07, 2021

Supplement to Prospectus [Text Block]

rr_SupplementToProspectusTextBlock

State Street Institutional Investment Trust

STATE STREET INCOME FUND

(SSASX)

(the “Fund”)

SUPPLEMENT DATED NOVEMBER 1, 2021 TO THE PROSPECTUS

AND SUMMARY PROSPECTUS, EACH DATED MAY 7, 2021,

AS EACH MAY BE SUPPLEMENTED FROM TIME TO TIME

Effective immediately, the Fund’s Prospectus and Summary Prospectus are revised as follows:

All references to “Bloomberg Barclays” are replaced with “Bloomberg” and other references to “Barclays” are removed.

State Street Income Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement to Prospectus [Text Block]

rr_SupplementToProspectusTextBlock

State Street Institutional Investment Trust

STATE STREET INCOME FUND

(SSASX)

(the “Fund”)

SUPPLEMENT DATED NOVEMBER 1, 2021 TO THE PROSPECTUS

AND SUMMARY PROSPECTUS, EACH DATED MAY 7, 2021,

AS EACH MAY BE SUPPLEMENTED FROM TIME TO TIME

Effective immediately, the Fund’s Prospectus and Summary Prospectus are revised as follows:

All references to “Bloomberg Barclays” are replaced with “Bloomberg” and other references to “Barclays” are removed.