Leases - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Lessee, Lease, Description [Line Items]
Extended lease term	10 years
Lessee, operating lease, termination period	1 year
Operating lease liabilities	$ 243	$ 273
Operating lease expense	21	26
Operating lease, impairment expense	20
Affiliated entity
Lessee, Lease, Description [Line Items]
Operating lease liabilities	$ 85	$ 99
Minimum
Lessee, Lease, Description [Line Items]
Lessee, operating lease, term of contract	1 year
Maximum
Lessee, Lease, Description [Line Items]
Lessee, operating lease, term of contract	18 years