Document and Entity Information	0 Months Ended
	Dec. 31, 2012
Risk/Return:
Document Type	485BPOS
Document Period End Date	Dec. 31, 2012
Registrant Name	MORGAN STANLEY INSTITUTIONAL FUND INC
Central Index Key	0000836487
Amendment Flag	false
Document Creation Date	Jul. 12, 2013
Document Effective Date	Jul. 15, 2013
Prospectus Date	Jul. 15, 2013
SMALL COMPANY GROWTH PORTFOLIO | Class IS
Risk/Return:
Trading Symbol	MFLLX