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Benefit Plans Actuarial Assumptions (Details)		3 Months Ended	12 Months Ended				48 Months Ended
	Oct. 01, 2021	Sep. 30, 2016	Sep. 30, 2020	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2018	Sep. 30, 2017	Oct. 01, 2016	Sep. 30, 2012
Defined Benefit Plan Disclosure
Amortization Period for Change in Benefit Obligation Related to 2016 Amendments to TVA Pension Plan				11 years
Rate of compensation increase		5.55%		5.55%	5.70%
Expected return on plan assets						7.25%
Period during which actual company compensation experience study performed				5 years
Rate of compensation increase				5.70%	5.70%	5.72%
Cost of living adjustment assumption												2.50%
Calculation Factor for Cola Calculation for TVA Pension Plan											0.25%
Pension Benefits
Defined Benefit Plan Disclosure
Discount rate		3.65%		3.65%	4.50%	4.45%
Rate of compensation increase		5.55%		5.55%	5.70%
Discount rate				4.50%	4.45%
Expected return on plan assets				7.00%	7.00%
Rate of compensation increase				5.70%	5.70%
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Discount rate		3.70%		3.70%	4.65%	4.50%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year				7.00%	7.50%	8.00%
Discount rate				4.65%	4.50%
Minimum
Defined Benefit Plan Disclosure
Rate of compensation increase		3.50%		3.50%
Cost of living adjustment assumption		1.00%		1.00%							1.00%
Maximum
Defined Benefit Plan Disclosure
Rate of compensation increase		13.00%		13.00%
Cost of living adjustment assumption		5.00%		5.00%							6.00%
Scenario, Forecast
Defined Benefit Plan Disclosure
Cost of living adjustment assumption			2.50%				2.50%	2.40%	2.00%	1.25%
Pre-Medicare Eligible [Member] | Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year				6.50%	7.00%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate				5.00%	5.00%
Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate		2019		2019	2019
Pre-Medicare Eligible [Member] | Scenario, Forecast | Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate			5.00%
Post-Medicare Eligible [Member] [Member] | Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year				0.00%	7.00%	7.50%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate		4.00%		5.00%	5.00%
Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate		2019		2019	2019						2021
Post-Medicare Eligible [Member] [Member] | Scenario, Forecast | Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year	4.00%						0.00%

X

- Definition

Amortization Period for Change in Benefit Obligation Related to 2016 Amendments to TVA Pension Plan

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

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The period in which an actual compensation experience study is performed at TVA to determine assumptions related to compensation increases for defined benefit plans.

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The interest rate used to adjust for the time value of money for the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
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Expected rate of compensation increases (for pay-related plans).

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The interest rate used to adjust for the time value of money.

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An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Expected rate of compensation increases (for pay-related plans).

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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.

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The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6514820

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The ultimate trend rate for health care costs.

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

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