Financial Risk Management Objectives and Policies - Summary of Sensitivity Analysis of Foreign Currency Risk (Parenthetical) (Detail)	Dec. 31, 2025	Dec. 31, 2024
Immatics US Inc [Member] \| Euro weakens by 10 against US dollars [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Percentage Of Reasonably Possible Decrease In Foreign Currency Risk	10.00%	10.00%
Immatics US Inc [Member] \| Euro strengthen by 10 against US dollars [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Percentage Of Reasonably Possible Decrease In Foreign Currency Risk	10.00%	10.00%
Immatics N.V. [Member] \| Immatics GmbH [Member] \| Euro weakens by 10 against US dollars [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Percentage Of Reasonably Possible Increase In Foreign Currency Risk	10.00%	10.00%
Immatics N.V. [Member] \| Immatics GmbH [Member] \| Euro strengthen by 10 against US dollars [Member]
Disclosure of Sensitivity Analysis For Each Type Of Market Risk [Line Items]
Percentage Of Reasonably Possible Increase In Foreign Currency Risk	10.00%	10.00%