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Benefit Plans Components of Benefit Plans (Details)	12 Months Ended		240 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2036 USD ($)	Oct. 01, 2016 Years
Defined Benefit Plan Disclosure
Fixed and variable fund annual maximum contribution	$ 10,000
Age Threshold for Changes to COLA Changes for Cash Balance Plan | Years				50
Defined contribution plan contribution amount	$ 80,000,000	$ 38,000,000
Minimum
Defined Benefit Plan Disclosure
Threshold for Deferral of Actuarial Gain/Loss Under Corridor Approach	10.00%
Scenario, Forecast
Defined Benefit Plan Disclosure
Minimum Funding for TVA Pension Plan Under 2016 Amendments			$ 300,000,000
Funded Status Threshold to Reduce Minimum Contribution Under 2016 Changes to TVA Pension Plan			100.00%

X

- Definition

Age Threshold for Changes to COLA Related to 2016 Amendments to TVA Pension Plan

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No definition available.

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- Definition

The maximum annual contribution that employees can make to the fixed and variable fund benefit. The fixed fund benefit is a benefit that earns a specified rate of interest on contributions made by employees. The variable fund is a benefit that invests employee contributions in the Spartan U.S. Equity Index Fund-Fidelity Advantage Class (Spartan).

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- Definition

Funded Status Threshold to Reduce Minimum Contribution Under 2016 Changes to TVA Pension Plan

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- Definition

Minimum Funding for TVA Pension Plan Under 2016 Changes

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- Definition

Threshold for Deferral of Actuarial Gain/Loss Under Corridor Approach

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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.

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No definition available.

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- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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