Document and Entity Information	3 Months Ended
	Mar. 31, 2026
Document and Entity Information
Document Type	POS AM
Entity Registrant Name	TERRESTRIAL ENERGY INC.
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Central Index Key	0002019804
Amendment Flag	false