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Commitments and Contingencies Commitments and Contingencies - Contingencies (Details) $ in Millions | 12 Months Ended
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Sep. 30, 2018 USD ($) Units reactors Insurance_layers Procedures | Sep. 30, 2017 USD ($) | Sep. 30, 2016 USD ($)
Contingencies |  |  |  |
Nuclear liability insurance |  | $ 450 |  |
Assessment from licensees for each licensed reactor |  | $ 127 |  |
Number of licensed reactors in US | reactors |  | 99 |  |
Nuclear accident assessment limitation per year per unit |  | $ 19 |  |
Number of licensed nuclear units | Units |  | 7 |  |
Maximum assessment per nuclear incident |  | $ 891 |  |
Total amount of protection available |  | $ 13,000 |  |
Number of layers until the U.S. Congress is required to take action | Insurance_layers |  | 2 |  |
Amount of property, decommissioning, and decontamination insurance carried |  | $ 5,100 |  |
Amount of insurance available for loss at any one site |  | 2,100 |  |
Maximum amount of retrospective premiums |  | 128 |  |
Maximum idemnity if a covered accident tasks or keeps a nuclear unit offline |  | 490 |  |
Maximum amount of retrospective premiums |  | 44 |  |
Estimated future decommissioning cost | [1] | $ 4,779 | $ 4,304 | $ 4,052
Number of procedures for determining estimates for the costs of nuclear decommissioning | Procedures |  | 2 |  |
Amount spent to reduce emissions since 1970 |  | $ 6,700 |  |
Amount spent to reduce emissions |  | 62 | 206 | 259
Possible additional future costs for compliance with Clean Air Act requirements |  | 163 |  |
Possible additional future costs for compliance with CCR requirements |  | 1,178 |  |
Possible additional future costs for compliance with Clean Water requirements. |  | 466 |  |
Estimated liability for cleanup and similar environmental work on a non-discounted basis |  | 12 | 7 |
Nuclear |  |  |  |
Contingencies |  |  |  |
Estimated future decommissioning cost |  | 2,989 | 2,859 | 2,492
Non-nuclear |  |  |  |
Contingencies |  |  |  |
Estimated future decommissioning cost |  | $ 1,790 | $ 1,445 | $ 1,560
[1] | (1) The current portions of the ARO liability in the amounts of $115 million and $128 million as of September 30, 2018 and 2017, respectively, are included in Accounts payable and accrued liabilities.

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- Definition The amount of property, decommissioning, and decontamination insurance available for loss at any one site to cover the cost of stabilizing or shutting down a reactor after an accident. + References No definition available. + Details
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- Definition The amount of property, decommissioning, and decontamination insurance carried for nuclear plants owned to cover the cost of stabilizing or shutting down a reactor after an accident. + References No definition available. + Details
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- Definition The amount spent to reduce emissions at power plants. + References No definition available. + Details
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- Definition The amount spent since 1970 to reduce emissions at power plants. + References No definition available. + Details
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- Definition An assessment from licensees for each licensed nuclear reactor in the United States to fund the second layer, the Secondary Financial Program. + References No definition available. + Details
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- Definition Maximum assessment per nuclear incident. + References No definition available. + Details
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- Definition The maximum idemnity per unit if an accident covered by the policy tasks or keeps a nuclear unit offline. + References No definition available. + Details
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- Definition The maximum amount of retrospective premiums that may be required for property, decommissioning, and decontamination insurance. + References No definition available. + Details
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- Definition The per year per unit limitation of the assessment for any nuclear accident + References No definition available. + Details
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- Definition For the first layer of protection all NRC nuclear plant licensees purchase nuclear insurance from American Nuclear Insurers for each nuclear plant with an operating license. + References No definition available. + Details
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- Definition Number of procedures for determining estimates for the costs of nuclear decommissioning + References No definition available. + Details
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- Definition The number of licensed reactors in US. + References No definition available. + Details
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- Definition The possible additional future costs for compliance with Clean Air Act requirements. + References No definition available. + Details
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- Definition The possible additional future costs for compliance with CCR requirements + References No definition available. + Details
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- Definition The possible additional future costs for compliance with Clean Water requirements. + References No definition available. + Details
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- Definition The maximum amount of retrospective premiums that could be required for accidental outage insurance. + References No definition available. + Details
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- Definition The total amount of protection available to compensate for losses arising from a nuclear event in the United States. + References No definition available. + Details
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- Definition The U.S. Congress is required to take action to provide additional funds to cover the additional losses if these layes are exhausted. + References No definition available. + Details
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- Definition Undiscounted amount of the accrual for environmental loss contingencies. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 5.Y.Q1) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 + Details
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