00101 - Document - Document And Entity Information {Elements} link:calculationLink link:presentationLink link:definitionLink 01102 - Document - Risk/Return Summary {Unlabeled} (MFS Institutional International Equity Fund) link:calculationLink link:presentationLink link:definitionLink 01103 - Schedule - Annual Fund Operating Expenses link:calculationLink link:presentationLink link:definitionLink 01104 - Schedule - Expense Example {Transposed} link:calculationLink link:presentationLink link:definitionLink 01105 - Schedule - Annual Total Returns link:calculationLink link:presentationLink link:definitionLink 01106 - Schedule - Average Annual Total Returns {Transposed} link:calculationLink link:presentationLink link:definitionLink 06108 - Document - Risk/Return Summary {Unlabeled} (MFS Institutional Large Cap Value Fund) link:calculationLink link:presentationLink link:definitionLink 06109 - Schedule - Annual Fund Operating Expenses link:calculationLink link:presentationLink link:definitionLink 06110 - Schedule - Expense Example {Transposed} link:calculationLink link:presentationLink link:definitionLink 06111 - Schedule - Annual Total Returns link:calculationLink link:presentationLink link:definitionLink 06112 - Schedule - Average Annual Total Returns {Transposed} link:calculationLink link:presentationLink link:definitionLink 06113 - Disclosure - Risk/Return Detail Data {Elements} (MFS Institutional Large Cap Value Fund) link:calculationLink link:presentationLink link:definitionLink