Long-Term Debt - Schedule of Long-term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Financing lease obligation	$ 6
Financing lease obligation		$ 7
Subtotal	1,341	943
Less: current maturities	(138)	(41)
Long-term debt	1,203	902
Convertible Notes
Debt Instrument [Line Items]
Unamortized discount on convertible notes	$ (31)	(34)
3.25 percent convertible notes due 2037 \| Convertible Notes
Debt Instrument [Line Items]
Interest rate (percent)	3.25%
Debt	$ 319	319
7.875 percent convertible notes due 2026 \| Convertible Notes
Debt Instrument [Line Items]
Interest rate (percent)	7.875%
Debt	$ 23	23
Term loan due 2024 \| Term Loan
Debt Instrument [Line Items]
Debt	$ 171	175
6.25 percent notes due 2024
Debt Instrument [Line Items]
Interest rate (percent)	6.25%
6.25 percent notes due 2024 \| Notes
Debt Instrument [Line Items]
Interest rate (percent)	6.25%
Debt	$ 445	444
Borrowings and securitization
Debt Instrument [Line Items]
Borrowings and securitization	$ 408	$ 9

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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Amount of short-term debt and current maturity of long-term debt and capital lease obligations due within one year or the normal operating cycle, if longer.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Present value of lessee's discounted obligation for lease payments from finance lease.

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Amount of long-term debt and lease obligation, classified as noncurrent.

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This is the principal amount outstanding for securitized loans only (across all types of loans).

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