Document and Entity Information	12 Months Ended
	Dec. 28, 2012
Risk/Return:
Document Type	485BPOS
Document Period End Date	Dec. 28, 2012
Registrant Name	JANUS INVESTMENT FUND
Central Index Key	0000277751
Amendment Flag	false
Document Creation Date	Dec. 28, 2012
Document Effective Date	Dec. 28, 2012
Prospectus Date	Dec. 28, 2012