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Asset Retirement Obligations Asset Retirement Obligations (Policies)
12 Months Ended
Sep. 30, 2020
Asset Retirement Obligation Disclosure [Abstract]  
Asset Retirement Obligations, Policy
Decommissioning Costs

    TVA recognizes legal obligations associated with the future retirement of certain tangible long-lived assets.  These obligations relate to fossil fuel-fired generating plants, nuclear generating plants, hydroelectric generating plants/dams, transmission structures, and other property-related assets.  These other property-related assets include, but are not limited to, easements and coal rights.  Activities involved with retiring these assets could include decontamination and demolition of structures, removal and disposal of wastes, and site restoration.  Revisions to the estimates of asset retirement obligations ("AROs") are made whenever factors indicate that the timing or amounts of estimated cash flows have changed materially.  Any accretion or depreciation expense related to these liabilities and assets is charged to a regulatory asset.  See Note 9 —
Regulatory Assets and Liabilities — Nuclear Decommissioning Costs and Non-Nuclear Decommissioning Costs and Note 12 — Asset Retirement Obligations.