Other Long-Term Assets (Details) - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2022	Sep. 30, 2022
Other Long-Term Assets
EnergyRight® receivables, net	$ 62	$ 62
Prepaid Expense, Noncurrent	63	74
Total other long-term assets	353	394
Prepaid Expense, Current	17	12
Loans and Leases Receivable, Allowance	3	3
Financing Receivable, after Allowance for Credit Loss, Current	3	6
EnergyRight loan reserve
Other Long-Term Assets
Loans and Leases Receivable, Allowance	1	1
Economic development loan specific loan reserve
Other Long-Term Assets
Loans and Leases Receivable, Allowance	1	1
Economic Development Loan Collective Reserve
Other Long-Term Assets
Loans and Leases Receivable, Allowance	1	1
Accounts Receivable [Member]
Other Long-Term Assets
EnergyRight® receivables, net	13	13
Other long-term assets
Other Long-Term Assets
Loans and other long-term receivables, net	106	99
EnergyRight® receivables, net	48	49
Other	93	70
Other long-term assets
Other Long-Term Assets
Commodity Contract Asset, Noncurrent	$ 43	$ 102
Energy Right
Other Long-Term Assets
Number of days in default	180 days
Energy Right \| Minimum
Other Long-Term Assets
Debt Instrument, Term	5 years
Energy Right \| Maximum
Other Long-Term Assets
Debt Instrument, Term	10 years

The number of days in default that are determined to be uncollectible.

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Other Long-Term Assets [Line Items]

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Carrying amount as of the balance sheet date of the asset arising from commodity contracts such as futures contracts tied to the movement of a particular commodity, which are expected to be converted into cash or otherwise disposed of after a year or beyond the normal operating cycle, if longer.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amortized cost, after allowance for credit loss, of financing receivable classified as current. Excludes net investment in lease.

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Amount, after allowance for credit loss, of financing receivable, classified as noncurrent.

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Amount of other miscellaneous assets expected to be realized or consumed after one year or normal operating cycle, if longer.

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Amount of noncurrent assets classified as other.

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Amount of asset related to consideration paid in advance for costs that provide economic benefits within a future period of one year or the normal operating cycle, if longer.

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Sum of the carrying amounts as of the balance sheet date of amounts paid in advance for expenses which will be charged against earnings in periods after one year or beyond the operating cycle, if longer.

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Carrying amount of financial assets accounted for as secured borrowings recognized in the transferor's statement of financial position at the end of each period presented.

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