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Asset Retirement Obligations Asset Retirement Obligations (Policies) | 12 Months Ended
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Sep. 30, 2015
Asset Retirement Obligation Disclosure [Abstract] |
Asset Retirement Obligations, Policy [Policy Text Block] | 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. Any accretion or depreciation expense related to these liabilities and assets is charged to a regulatory asset. See Note 9 — Nuclear Decommissioning Costs and Non-Nuclear Decommissioning Costs and Note 13. To estimate its decommissioning obligation related to its nuclear generating stations, TVA uses a probability-weighted, discounted cash flow model which, on a unit-by-unit basis, considers multiple outcome scenarios that include significant estimations and assumptions. Those assumptions include (1) estimates of the cost of decommissioning, (2) the method of decommissioning and the timing of the related cash flows, (3) the license period of the nuclear plant, considering the probability of license extensions, (4) cost escalation factors, and (5) the credit adjusted risk free rate to measure the obligation at the present value of the future estimated costs. Prior to June 30, 2014, TVA based its decommissioning cost estimates on cost elements prescribed by the NRC to dismantle and decommission the radioactive portion of each site with the assumption that decommissioning would occur within the first seven years after plant shut down, which approximates the DECON method of decommissioning. The DECON method requires that radioactive contamination is removed from a site and safely disposed of or decontaminated to a level that permits the site to be released for unrestricted use shortly after it ceases operation. On June 30, 2014, TVA recorded a change in estimate based on site-specific decommissioning cost studies. Additionally, TVA determined it appropriate to reflect an increase in the probability that certain of its nuclear operating licenses will be extended and that there is a probability that it will be able to delay ultimate decommissioning activities under a SAFSTOR method of decommissioning. The SAFSTOR method allows nuclear facilities to be placed and maintained in a condition that allows the facilities to be safely stored and subsequently decontaminated to levels that permit release for unrestricted use. As such, TVA ascribed probabilities to both the SAFSTOR and DECON methods of decommissioning in order to estimate its decommissioning obligation. Decommissioning cost studies will be updated for each of TVA’s nuclear units at least every five years.

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- Definition Disclosure of accounting policy for determining amounts to accrue and charge against earnings so as to satisfy legal obligations associated with the retirement (through sale, abandonment, recycling, or disposal in some other manner) of a tangible long-lived asset that result from the acquisition, construction, or development and (or) the normal operation of a long-lived asset. This accounting policy disclosure excludes obligations arising 1) in connection with leased property, whether imposed by a lease agreement or by a party other than the lessor, that meet the definition of either minimum lease payments or contingent rentals; 2) solely from a plan to sell or otherwise dispose of a long-lived asset and 3) from certain environmental remediation liabilities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=51655414&loc=d3e18780-107790 + Details
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