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Regulatory Assets and Liabilities | 6 Months Ended
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Mar. 31, 2018
Regulatory Assets and Liabilities Disclosure [Abstract] |
Regulatory Assets and Liabilities | Regulatory Assets and Liabilities Regulatory assets generally represent incurred costs that have been deferred because such costs are probable of future recovery in customer rates. Regulatory liabilities generally represent obligations to make refunds to customers for previous collections for costs that are not likely to be incurred or deferrals of gains that will be credited to customers in future periods. Components of regulatory assets and regulatory liabilities are summarized in the table below:
Regulatory Assets and Liabilities
| At March 31, 2018 |  | At September 30, 2017
Current regulatory assets |  |  |
Deferred nuclear generating units | $ | 237 |  |  | $ | 237 |
Unrealized losses on interest rate derivatives | 80 |  |  | 93 |
Unrealized losses on commodity derivatives | 44 |  |  | 68 |
Fuel cost adjustment receivable | 39 |  |  | 1 |
Environmental agreements | 3 |  |  | 2 |
Environmental cleanup costs - Kingston ash spill | 44 |  |  | 44 |
Gallatin coal combustion residual facilities | 21 |  |  | — |
Other current regulatory assets | 3 |  |  | 2 |
Total current regulatory assets | 471 |  |  | 447 |
Non-current regulatory assets |  |  |  |  |
Deferred pension costs and other post-retirement benefits costs | 3,881 |  |  | 4,009 |
Unrealized losses on interest rate derivatives | 824 |  |  | 982 |
Gallatin coal combustion residual facilities | 878 |  |  | 899 |
Nuclear decommissioning costs | 821 |  |  | 823 |
Deferred nuclear generating units | 645 |  |  | 759 |
Non-nuclear decommissioning costs | 701 |  |  | 703 |
Environmental cleanup costs - Kingston ash spill | 242 |  |  | 263 |
Unrealized losses on commodity derivatives | 36 |  |  | 9 |
Environmental agreements | 11 |  |  | 13 |
Other non-current regulatory assets | 201 |  |  | 238 |
Total non-current regulatory assets | 8,240 |  |  | 8,698 |
Total regulatory assets | $ | 8,711 |  |  | $ | 9,145 |
Current regulatory liabilities |  |  |  |  |
Fuel cost adjustment tax equivalents | $ | 147 |  |  | $ | 153 |
Fuel cost adjustment | — |  |  | 2 |
Unrealized gains on commodity derivatives | 12 |  |  | 8 |
Total current regulatory liabilities | 159 |  |  | 163 |
Non-current regulatory liabilities |  |  |  |  |
Deferred other post-retirement benefits cost | 16 |  |  | 23 |
Unrealized gains on commodity derivatives | 3 |  |  | 2 |
Total non-current regulatory liabilities | 19 |  |  | 25 |
Total regulatory liabilities | $ | 178 |  |  | $ | 188 |

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- Definition The entire disclosure for detailed information about regulatory assets and liabilities, including current and noncurrent assets created when regulatory agencies permit the deferral of costs to the balance sheet that would otherwise be required to appear on the company's income statement and would be charged against current expenses or revenues, as well as current and noncurrent liabilities created when regulatory agencies permit. + References No definition available. + Details
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