Actual Return on Plan Assets

No definition available.

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- Definition

COLA percentage increase (decrease)

+ References

No definition available.

+ Details

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- Definition

The cost of living adjustment percentage used for defined benefit plans.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

The cost of living adjustment percentage used for defined benefit plans for next fiscal year.

+ References

No definition available.

+ Details

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- Definition

Initial health care cost trend rate

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Year health care cost ultimate trend rate is expected to be reached for Net Benefit Cost Assumption

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

+ References

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ References

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Weighted-average interest crediting rate used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, cash balance and other defined benefit plans with promised interest crediting rate.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 8
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e2919-114920

+ Details

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Data Type:	dtr-types:percentItemType
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Period Type:	duration

- Definition

Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ References

+ Details

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Period Type:	duration

- Definition

Weighted-average interest crediting rate used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, cash balance and other defined benefit plans with promised interest crediting rate.

+ References

+ Details

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Period Type:	duration

- 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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- Definition

Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status.

+ References

+ Details

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Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Ultimate trend rate for health care cost for defined benefit postretirement plan.

+ References

+ Details

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Period Type:	instant

- Definition

Year ultimate health care cost trend rate is expected to be reached, in YYYY format.

+ References

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

Name:	tve_BenefitPlanParticipantClassAxis=tve_PostMedicareEligibleMemberMember
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- Details

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- Details

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- Details

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Benefit Plans Actuarial Assumptions (Details) - USD ($)	12 Months Ended
Benefit Plans Actuarial Assumptions (Details) - USD ($)	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure
Defined Benefit Plan, Cost of Living Adjustment Assumption	0.25%
Pension Benefits
Defined Benefit Plan Disclosure
Discount rate	2.90%	2.75%	3.20%
Discount rate	5.60%	2.90%	2.75%
Rate of compensation increase	3.32%	3.37%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate	5.14%	5.15%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Weighted-Average Interest Crediting Rate	5.14%	5.15%	5.15%
Expected return on plan assets	5.75%	6.75%	6.75%
Defined Benefit Plan, Cost of Living Adjustment Assumption	2.00%	2.00%	2.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase		3.37%	3.43%
COLA percentage increase (decrease)	6.00%
Actual Return on Plan Assets	(6.64%)	20.30%	5.11%
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Discount rate	3.05%	3.05%	3.30%
Discount rate	5.65%	3.05%
Defined Benefit Plan, Cost of Living Adjustment Assumption	2.00%	2.00%	2.00%
Minimum
Defined Benefit Plan Disclosure
Rate of compensation increase	2.50%
Maximum
Defined Benefit Plan Disclosure
Rate of compensation increase	14.00%
Scenario, Forecast \| Pension Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Cost of Living Adjustment Assumption Next Fiscal Year				315.00%	6.00%
Post-Medicare Eligible [Member] [Member] \| Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Current health care cost trend rate	0.00%	0.00%	0.00%
Ultimate health care cost trend rate	4.00%	4.00%	4.00%
Year health care cost ultimate trend rate is reached for Net Benefit Cost Assumption	2024	2024	2023
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2026	2024
Pre-Medicare Eligible per Capita Claim Costs \| Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Current health care cost trend rate	6.25%	6.50%	6.75%
Ultimate health care cost trend rate	5.00%	5.00%	5.00%
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2031	2027	2027
Initial health care cost trend rate	$ 0.0700	$ 0.0625
Pre-Medicare Eligible per Capita Claim Costs \| Pension Costs [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2027
Pre-Medicare Eligible per Capita Contributions \| Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Current health care cost trend rate	8.51%	11.93%	6.75%
Ultimate health care cost trend rate	5.00%	5.00%	5.00%
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2022	2027	2027
Initial health care cost trend rate	$ 0.0500	$ 0.0851
Pre-Medicare Eligible per Capita Contributions \| Pension Costs [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2027