Short-Term and Long-Term Debt - Carrying Amount and Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2025	Sep. 30, 2025
Debt Instrument [Line Items]
Current portion of long-term debt, carrying value	$ 64	$ 2
Long-term debt, carrying amount	2,574	2,614
Reported Value Measurement
Debt Instrument [Line Items]
Current portion of long-term debt, carrying value		2
Long-term debt, carrying amount		2,614
Estimate of Fair Value Measurement
Debt Instrument [Line Items]
Current portion of long-term debt, fair value	64	2
Estimate of Fair Value Measurement | Fair Value, Inputs, Level 2
Debt Instrument [Line Items]
Long-term debt, fair value	$ 2,301	$ 2,350