Debt and Other Obligations Debt and Other Obligations - Put and Call Options (Details) $ in Millions	12 Months Ended
	Sep. 30, 2025 USD ($)
PARRS 1998 Series D Bond
Debt Instrument
Amount of redeemable bond issues outstanding	$ 256
PARRS interest rate prior to rate reset	6.75%
PARRS interest rate after rate reset	2.134%
Amount of bonds redeemed	$ 318
PARRS 1999 Series A Bond
Debt Instrument
Amount of redeemable bond issues outstanding	$ 208
PARRS interest rate prior to rate reset	6.50%
PARRS interest rate after rate reset	2.216%
Amount of bonds redeemed	$ 316