Document and Entity Information - shares
6 Months Ended
Jun. 30, 2019
Aug. 05, 2019
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2  
Trading Symbol ALRN  
Entity Registrant Name Aileron Therapeutics Inc  
Entity Central Index Key 0001420565  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period true  
Entity Common Stock, Shares Outstanding   27,810,358
Entity File Number 001-38130  
Entity Tax Identification Number 134196017  
Entity Address, Address Line One 490 Arsenal Way  
Entity Address, Address Line Two Suite 210  
Entity Address, City or Town Watertown  
Entity Address, State or Province MA  
Entity Address, Postal Zip Code 02472  
City Area Code 617  
Local Phone Number 995-0900  
Entity Shell Company false  
Entity Current Reporting Status Yes