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Debt and Other Obligations Debt Securities Activity (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Jun. 30, 2020 | Jun. 30, 2019 | Sep. 30, 2019 | Sep. 30, 2018
Debt Instrument |  |  |  |  |  |  |  |  |
Total long-term debt, net |  | $ 19,001 |  |  | $ 19,001 |  |  | $ 20,183 |
Redemptions and repurchases of power bonds |  |  |  |  | $ 1,286 | [1] | $ 1,034 |  |
Variable Interest Entity, Financial or Other Support, Type |  |  |  |  | 20 |  |  |  |
Total redemptions/maturities of debt | [1] |  |  |  | $ (1,329) |  |  |  |
Proceeds from Issuance of Debt |  |  |  |  | 997 |  | 0 |  |
Debt Instrument, Unamortized Discount |  | (3) |  |  | (3) |  |  |  |
Repayments of Notes Payable |  |  |  |  | 23 |  | $ 46 |  |
2020 Series A |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Debt |  |  |  |  | 1,000 |  |  |  |
electronotes [Member] |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Redemptions and repurchases of power bonds |  | 1 |  | $ 217 |  |  |  |  |
2009 Series B [Member] |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Redemptions and repurchases of power bonds |  | $ 27 | $ 1,000 | $ 1 |  |  |  |  |
Debt of variable interest entities [Member] |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Other Debt instrument, Interest Rate, Effective Percentage |  |  |  |  |  |  |  |  | 4.32%
1998 Series D |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Redemptions and repurchases of power bonds |  |  |  |  | 17 |  |  |  |
1999 Series A Member |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Redemptions and repurchases of power bonds |  |  |  |  | $ 23 |  |  |  |
2020 Series A |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 0.75% |  |  | 0.75% |  |  |  |
electronotes [Member] |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 2.65% |  | 3.33% | 2.65% |  |  |  |
1998 Series D |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 3.55% |  |  | 3.55% |  |  |  |
1999 Series A Member |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 3.36% |  |  | 3.36% |  |  |  |
2009 Series B [Member] |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 3.77% | 2.25% | 3.77% | 3.77% |  |  |  |
Notes Payable [Member] |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 1.64% |  |  | 1.64% |  |  |  |
[1] | (1) The 2020 Series A Power Bonds were issued at 99.7 percent of par. (2) All redemptions were at 100 percent of par.

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