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Fair Value Measurements Fair Value Measurements - Fair Value Measurements Using Significant Unobservable Inputs (Details) tons-per-year in Billions | 12 Months Ended |
--- | --- | ---
Sep. 30, 2018 USD ($) tons-per-year | Sep. 30, 2017 USD ($) tons-per-year | Sep. 30, 2016 USD ($)
Fair Value Measurements |  |  |
Commodity contract derivatives, assets | $ 72,000,000 | $ 10,000,000 |
Commodity contract derivatives, liabilities | $ 12,000,000 | $ 70,000,000 |
Minimum |  |  |
Assets |  |  |
Fair value measurements tons per year | tons-per-year | 0.7 | 0.6 |
Price per ton | $ 12.25 | $ 11.40 |
Liabilities |  |  |
Fair value measurements tons per year | tons-per-year | 0.7 | 0.6 |
Price per ton | $ 12.25 | $ 11.40 |
Maximum |  |  |
Assets |  |  |
Fair value measurements tons per year | tons-per-year | 0.8 | 0.7 |
Price per ton | $ 112.24 | $ 112.23 |
Liabilities |  |  |
Fair value measurements tons per year | tons-per-year | 0.8 | 0.7 |
Price per ton | $ 112.24 | $ 112.23 |
Commodity Contract Derivatives |  |  |
Fair Value Measurements |  |  |
Balance at beginning/end of period | 58,000,000 | (67,000,000) | $ (127,000,000)
Purchases | 0 | 0 |
Issuances | 0 | 0 |
Sales | 0 | 0 |
Settlements | 0 | 0 |
Change in net unrealized gains (losses) deferred as regulatory assets and liabilities | 125,000,000 | 60,000,000 |
Fair Value, Inputs, Level 3 |  |  |
Fair Value Measurements |  |  |
Commodity contract derivatives, assets | 59,000,000 | 2,000,000 |
Commodity contract derivatives, liabilities | $ 1,000,000 | $ 69,000,000 |

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- Definition The fair value as of the balance sheet date of firm holdings in physical commodity contracts (for example, agricultural products, metals and energy). Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings. + References No definition available. + Details
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