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v3.23.3

Benefit Plans Sensitivity to Certain Changes in Pension Assumptions (Details) - USD ($) | 12 Months Ended
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Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
Defined Benefit Plan Disclosure |  |  |
Defined Benefit Plan, Cost of Living Adjustment Assumption | 0.25% |  |
Discount rate |  |  |
Defined Benefit Plan Disclosure |  |  |
Change in Assumption | (0.25%) |  |
Impact on Pension Cost | $ 12,000,000 |  |
Impact on Projected Benefit Obligation | $ 236,000,000 |  |
Rate of return on plan assets |  |  |
Defined Benefit Plan Disclosure |  |  |
Change in Assumption | (0.25%) |  |
Impact on Pension Cost | $ 19,000,000 |  |
Cost of Living Adjustments [Domain] |  |  |
Defined Benefit Plan Disclosure |  |  |
Change in Assumption | 0.25% |  |
Impact on Pension Cost | $ 24,000,000 |  |
Impact on Projected Benefit Obligation | $ 165,000,000 |  |
Other Post-retirement Benefits |  |  |
Defined Benefit Plan Disclosure |  |  |
Defined Benefit Plan, Cost of Living Adjustment Assumption | 2.00% | 2.00% | 2.00%
Discount rate | 6.05% | 5.65% | 305.00%
Actuarial assumption COLA | $ 0.06 | $ 0.035 | $ 0.0113
Pension Benefits |  |  |
Defined Benefit Plan Disclosure |  |  |
Defined Benefit Plan, Cost of Living Adjustment Assumption | 2.00% | 2.00% | 2.00%
COLA percentage increase (decrease) | 6.00% |  |
Discount rate | 5.95% | 5.60% | 2.90%

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- Definition Actuarial assumption COLA + References No definition available. + Details
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- Definition COLA percentage increase (decrease) + References No definition available. + Details
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Balance Type: | na
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- Definition The change in the discount date or the rate of return on plan assets assumption that is used in disclosure of sensitivity of the net periodic pension cost and the projected benefit obligation to changes in those rates. + 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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Balance Type: | na
Period Type: | instant

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- Definition Amount of effect of change in rate on the net periodic benefit cost for pension benefits. + References No definition available. + Details
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Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Amount of effect of change in rate on the projected benefit obligation for pension benefits. + References No definition available. + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- 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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- Details
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- Details
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- Details
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