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Gallatin Coal Combustion Residual Facilities Regulatory Accounting Treatment (Policies) | 3 Months Ended
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Dec. 31, 2017
Regulatory Asset Accounting Treatment [Abstract] |
Regulatory Asset Accounting Treatment [Table Text Block] | 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 amounts are included in rates or paid out.

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