Leases (Details) - USD ($) $ in Millions	Jun. 30, 2025	Sep. 30, 2024
Amounts Recognized on TVA's Consolidated Balance Sheet [Line Items]
Finance lease, asset	$ 684	$ 729
Operating Lease, Liability, Current	56	63
Operating Lease, Liability, Noncurrent	$ 74	$ 88

[Line Items] for Amounts Recognized on TVA's Consolidated Balance Sheet [Table]

No definition available.

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- Definition

Finance lease, asset

+ References

No definition available.

+ Details

Name:	tve_Financeleaseasset
Namespace Prefix:	tve_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease, classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-1

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease, classified as noncurrent.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant