GOODWILL AND INTANGIBLE ASSETS - Schedule of Intangible Assets Acquired (Detail) $ in Millions	12 Months Ended
	Sep. 30, 2025 USD ($)
Intangible Asset, Acquired, Finite-Lived [Line Items]
Intangible assets subject to amortization	$ 125
intangible Assets, Acquired During the Period	136
Trademarks and trade names
Intangible Asset, Acquired, Finite-Lived [Line Items]
Intangible assets not subject to amortization	11
Technology
Intangible Asset, Acquired, Finite-Lived [Line Items]
Intangible assets subject to amortization	$ 71
Technology \| Minimum
Intangible Asset, Acquired, Finite-Lived [Line Items]
Amortization Period (in years)	10 years
Technology \| Maximum
Intangible Asset, Acquired, Finite-Lived [Line Items]
Amortization Period (in years)	20 years
Order backlog
Intangible Asset, Acquired, Finite-Lived [Line Items]
Intangible assets subject to amortization	$ 17
Amortization Period (in years)	1 year
Order backlog \| Minimum
Intangible Asset, Acquired, Finite-Lived [Line Items]
Amortization Period (in years)	1 year
Order backlog \| Maximum
Intangible Asset, Acquired, Finite-Lived [Line Items]
Amortization Period (in years)	3 years
Customer relationships
Intangible Asset, Acquired, Finite-Lived [Line Items]
Intangible assets subject to amortization	$ 37
Customer relationships \| Minimum
Intangible Asset, Acquired, Finite-Lived [Line Items]
Amortization Period (in years)	10 years
Customer relationships \| Maximum
Intangible Asset, Acquired, Finite-Lived [Line Items]
Amortization Period (in years)	20 years

TransDigm Group INC 10-K