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Related Parties Related Parties (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2016
Related Parties |  |  |  |  |  |  |  |  |  |  |
Remaining appropriation investment | $ 258 |  |  |  | $ 258 |  |  |  | $ 258 | $ 258 |
Current borrowing capacity | 150 |  |  |  |  |  |  |  | 150 |  |
Revenue from sales of electricity | 3,185 | $ 2,707 | $ 2,792 | $ 2,549 | 3,075 | $ 2,571 | $ 2,547 | $ 2,546 | 11,233 | 10,739 | $ 10,616
Return on power program appropriation investment |  |  |  |  |  |  |  |  | (5) | (5) | (6)
Related Party Transactions |  |  |  |  |  |  |  |  |  |  |
Related Parties |  |  |  |  |  |  |  |  |  |  |
Revenue from sales of electricity |  |  |  |  |  |  |  |  | 122 | 126 | 126
Other income |  |  |  |  |  |  |  |  | 240 | 136 | 161
Operating expenses |  |  |  |  |  |  |  |  | 220 | 216 | 216
Additions to property, plant, and equipment |  |  |  |  |  |  |  |  | 8 | 16 | 32
Cash and cash equivalents | 46 |  |  |  | 46 |  |  |  | 46 | 46 | 54
Accounts receivable, net | 60 |  |  |  | 84 |  |  |  | 60 | 84 | 68
Receivables, Long-term Contracts or Programs | 46 |  |  |  | 35 |  |  |  | 46 | 35 | 61
Accounts payable and accrued liabilities | 69 |  |  |  | 71 |  |  |  | 69 | 71 | 77
Long-term power bonds, net | $ 0 |  |  |  | $ 1 |  |  |  | 0 | 1 | 4
Return on power program appropriation investment |  |  |  |  |  |  |  |  | $ (5) | $ (5) | $ (6)

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- Definition Balance of appropriated funds advanced and property transferred to/from the reporting entity by the U.S. government as an investment in its power program. + References No definition available. + Details
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- Definition Including the current and noncurrent portions, carrying value as of the balance sheet date of other forms of uncollateralized debt obligations not elsewhere specified in the taxonomy(with maturities initially due after one year or beyond the operating cycle if longer). + References No definition available. + Details
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- Definition This element represents disclosure of the cash payments from net power proceeds paid annually to the U.S. government as a return on the government's appropriation investment in the reporting entity. + References No definition available. + Details
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- Definition Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Excludes cash and cash equivalents within disposal group and discontinued operation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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