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Summary of Significant Accounting Policies Leases (Details)	6 Months Ended
	Mar. 31, 2020
Lease obligation related to Purchased Power [Line Items]
Lease obligation related to Purchased Power [Table Text Block]	296

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- Definition

[Line Items] for Lease obligation related to Purchased Power

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No definition available.

+ Details

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- Definition

[Table Text Block] for Lease obligation related to Purchased Power

+ References

No definition available.

+ Details

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Namespace Prefix:	tve_
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