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Plant Closures (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended	57 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Sep. 30, 2023
Property, Plant and Equipment [Line Items]
Accelerated depreciation						$ 659,000,000
Depreciation expense	$ 450,000,000	$ 481,000,000	$ 902,000,000	$ 947,000,000
Accumulated additional depreciation		$ 37,000,000		$ 73,000,000
Cumberland
Property, Plant and Equipment [Line Items]
Accelerated depreciation	$ 16,000,000
Accumulated additional depreciation					$ 80,000,000

X

- Definition

Accelerated depreciation

+ References

No definition available.

+ Details

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Namespace Prefix:	tve_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Accumulated additional depreciation

+ References

No definition available.

+ Details

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Namespace Prefix:	tve_
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Balance Type:	credit
Period Type:	duration

X

- Definition

The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482099/360-10-50-1

+ Details

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X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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