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Gallatin coal combustion residual facilities Regulatory Asset Treatment (Policies) | 12 Months Ended
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Sep. 30, 2018
Accounting Policies [Abstract] |
Regulatory Asset Accounting Treatment [Table Text Block] | Financial Impact In August 2017, TVA began using regulatory accounting treatment to defer expected future costs of compliance with orders or settlements related to lawsuits involving the Gallatin CCR facilities. The TVA Board approved a plan to amortize these costs over the anticipated duration of the Gallatin CCR facilities project (excluding post-closure care), beginning October 1, 2018, as project costs are incurred.

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