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Commitments and Contingencies Commitments and Contingencies - Contingencies (Details) $ in Millions | 12 Months Ended
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Sep. 30, 2019 USD ($) Units Insurance_layers Procedures reactors | Sep. 30, 2018 USD ($) | Sep. 30, 2017 USD ($)
Contingencies |  |  |  |
Loss Contingency, Damages Sought, Value |  | $ 30 |  |
Nuclear liability insurance |  | 450 |  |
Assessment from licensees for each licensed reactor |  | $ 138 |  |
Number of licensed reactors in US | reactors |  | 98 |  |
Nuclear accident assessment limitation per year per unit |  | $ 20 |  |
Number of licensed nuclear units | Units |  | 7 |  |
Maximum assessment per nuclear incident |  | $ 963 |  |
Total amount of protection available |  | $ 14,000 |  |
Number of layers until the U.S. Congress is required to take action | Insurance_layers |  | 2 |  |
Amount of insurance available for loss at any one site |  | $ 2,100 |  |
Maximum amount of retrospective premiums |  | 139 |  |
Maximum idemnity if a covered accident tasks or keeps a nuclear unit offline |  | 490 |  |
Maximum amount of retrospective premiums |  | 46 |  |
Estimated future decommissioning cost | [1] | $ 5,616 | $ 4,779 | $ 4,304
Number of procedures for determining estimates for the costs of nuclear decommissioning | Procedures |  | 2 |  |
Amount spent to reduce emissions since 1970 |  | $ 6,800 |  |
Amount spent to reduce emissions |  | 17 | 62 | 206
Possible additional future costs for compliance with Clean Air Act requirements |  | 142 |  |
Possible additional future costs for compliance with CCR requirements |  | 1,181 |  |
Possible additional future costs for compliance with Clean Water requirements. |  | 278 |  |
Estimated liability for cleanup and similar environmental work on a non-discounted basis |  | 15 | 12 |
Nuclear |  |  |  |
Contingencies |  |  |  |
Estimated future decommissioning cost |  | 3,136 | 2,989 | 2,859
Non-nuclear |  |  |  |
Contingencies |  |  |  |
Estimated future decommissioning cost |  | $ 2,480 | $ 1,790 | $ 1,445
[1] | (1) The current portions of the ARO liability in the amounts of $163 million and $115 million at September 30, 2019 and 2018, 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 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 The possible additional future costs for compliance with Clean Air Act requirements. + 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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