Leases (Details)	12 Months Ended
	Sep. 30, 2025 USD ($) Units	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Lessee, Lease, Description [Line Items]
Operating Lease, Right-of-Use Asset	$ 113,000,000	$ 149,000,000
Finance Lease, Right-of-Use-Asset, after Accumulated Amortization	663,000,000	729,000,000
Total lease assets	776,000,000	878,000,000
Operating Lease Liability Current	46,000,000	63,000,000
Current Finance Lease Liability	$ 86,000,000	$ 80,000,000
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other long-term liabilities	Other long-term liabilities
Total lease liabilities	$ 835,000,000	$ 931,000,000
Operating Lease, Cost	73,000,000	77,000,000	$ 69,000,000
Variable Lease, Cost	337,000,000	258,000,000	134,000,000
Short-term Lease, Cost	15,000,000	10,000,000	18,000,000
Finance Lease, Right-of-Use Asset, Amortization	91,000,000	79,000,000	57,000,000
Finance Lease, Interest Expense	46,000,000	37,000,000	43,000,000
Total finance lease costs	137,000,000	116,000,000	100,000,000
Lease, Cost	562,000,000	461,000,000	$ 321,000,000
Operating lease under PPA	75,000,000	121,000,000
Finance Lease, Liability, Noncurrent	640,000,000	700,000,000
Leases
Finance lease under PPA	509,000,000	$ 550,000,000
Expected Capacity Payments - PPA Leases	$ 862,000,000
Number of PPAs for solar generation and discharge battery energy storage system | Units	3
Lessee, Finance Lease, Remaining Lease Term	21 years