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Plant Closures (Details) - USD ($)	3 Months Ended		6 Months Ended		24 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021
Property, Plant and Equipment [Line Items]
Accelerated depreciation	$ 34,000,000	$ 91,000,000	$ 67,000,000	$ 316,000,000	$ 1,000,000,000.0

X

- Definition

Accelerated depreciation

+ References

No definition available.

+ Details

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

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

Name:	us-gaap_PropertyPlantAndEquipmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration