Goodwill and Other Intangible Assets - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2025	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Finite-Lived Intangible Assets [Line Items]
Goodwill and intangible asset impairment	$ 0	$ 224,000,000	$ 0	$ 158,000,000
Impairment		161,000,000		158,000,000
Goodwill		3,839,000,000	3,993,000,000	3,529,000,000
Amortization of intangible assets		152,000,000	155,000,000	116,000,000
Estimated amortization expense in 2026		131,000,000
Estimated amortization expense in 2027		122,000,000
Estimated amortization expense in 2028		111,000,000
Estimated amortization expense in 2029		73,000,000
Estimated amortization expense in 2030		$ 71,000,000
Goodwill, Impairment Loss, Statement of Income or Comprehensive Income [Extensible Enumeration]		Goodwill and intangible asset impairment
Intangible assets, net (excluding goodwill)		$ 864,000,000	1,066,000,000
Impairment of assets		$ 63,000,000
Impairment Of Intangible Asset Finite Lived Statement Of Income Or Comprehensive Income Extensible Enumeration Not Disclosed Flag		pre-tax, non-cash intangible asset impairment charge
Software products
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets		$ 11,000,000	12,000,000	11,000,000
Sensia
Finite-Lived Intangible Assets [Line Items]
Reporting unit, carrying value				$ 665,000,000
Impairment		161,000,000
Goodwill			$ 161,000,000
Intangible assets, net (excluding goodwill)		58,000,000
Finite-Lived Intangible Assets, Fair Value Disclosure		$ 58,000,000