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Debt and Finance Leases - Schedule of Long-term Debt and Finance Leases (Details) - USD ($) $ in Millions |  |  |  | 12 Months Ended |  |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 21, 2018 | Jan. 24, 2017 | Jun. 30, 2016 | Dec. 31, 2019 | Dec. 31, 2018 | May 28, 2019 | May 24, 2019 | May 14, 2019 | Nov. 05, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Dec. 07, 2017 | Aug. 02, 2016 | May 23, 2016
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 6,042 | $ 6,691 |  |  |  |  |  |  |  |  |
Finance leases |  |  |  |  | 1 |  |  |  |  |  |  |  |  |
Subtotal long-term debt and finance leases (including current maturities) |  |  |  | 6,042 | 6,692 |  |  |  |  |  |  |  |  |
Less current maturities |  |  |  | (88) | (72) |  |  |  |  |  |  |  |  |
Less debt issuance costs |  |  |  | (65) | (70) |  |  |  |  |  |  |  |  |
Discounts |  |  |  | (86) | (101) |  |  |  |  |  |  |  |  |
Total long-term debt and finance leases |  |  |  | 5,803 | 6,449 |  |  |  |  |  |  |  |  |
Debt Instrument, Unamortized Discount [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total discounts |  |  |  | (86) | (101) |  |  |  |  |  |  |  |  |
Recourse Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | 6,008 | 6,523 |  |  |  |  |  |  |  |  |
Recourse Debt | Senior Notes, due 2024 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 0 | 733 |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  | 6.25% |  |  |  |  |  |  |  |  |  |
Recourse Debt | Senior Notes, due 2026 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 1,000 | 1,000 |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  | 7.25% |  |  |  |  |  |  |  |  |  | 7.25%
Recourse Debt | Senior Notes, due 2027 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 1,230 | 1,230 |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  | 6.625% |  |  |  |  |  | 6.625% |  |  | 6.625% |
Recourse Debt | Senior Notes, due 2028 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 821 | 821 |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  | 5.75% |  |  |  |  |  | 5.75% | 5.75% | 5.75% |  |
Recourse Debt | Senior Notes due 2029 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 733 | 0 |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  | 5.25% |  |  | 5.25% | 5.25% |  |  |  |  |  |
Recourse Debt | Convertible Senior Notes Due 2048 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 575 | 575 |  |  |  |  |  |  |  |  |
Discounts |  |  |  | $ 85 | $ 96 |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  | 2.75% |  |  |  |  |  |  |  |  |  |
Effective rate |  |  |  | 5.05% | 5.02% |  |  |  |  |  |  |  |  |
Debt Instrument, Unamortized Discount [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total discounts |  |  |  | $ 85 | $ 96 |  |  |  |  |  |  |  |  |
Recourse Debt | Senior Secured First Lien Notes, due 2024 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 600 | 0 |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  | 3.75% |  | 3.75% |  |  |  |  |  |  |  |
Recourse Debt | Senior Secured First Lien Notes, due 2029 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 500 | 0 |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  | 4.45% |  | 4.45% |  |  |  |  |  |  |  |
Recourse Debt | Term Loan Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  | $ 1,900 | $ 0 | 1,698 |  |  |  | $ 260 |  |  |  |  |
Discounts |  |  |  | 0 | 4 |  |  |  |  |  |  |  |  |
Debt Instrument, Unamortized Discount [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total discounts |  |  |  | $ 0 | $ 4 |  |  |  |  |  |  |  |  |
Recourse Debt | Term Loan Facility | LIBOR |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate (as a percent) | 1.75% | 2.25% | 2.75% | 1.75% | 1.75% |  |  |  |  |  |  |  |  |
Recourse Debt | Tax-exempt bonds |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 466 | $ 466 |  |  |  |  |  |  |  |  |
Recourse Debt | Tax-exempt bonds | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  | 4.125% |  |  |  |  |  |  |  |  |  |
Recourse Debt | Tax-exempt bonds | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  | 6.00% |  |  |  |  |  |  |  |  |  |
Recourse Debt | Senior Secured First Lien Notes, due 2024 and 2029 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Discounts |  |  |  | $ 1 | 0 |  |  |  |  |  |  |  |  |
Debt Instrument, Unamortized Discount [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total discounts |  |  |  | 1 | 0 |  |  |  |  |  |  |  |  |
Line of Credit | Revolver Facility | Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 83 | 0 |  |  |  |  |  |  |  |  |
Line of Credit | Revolver Facility | Revolving Credit Facility | LIBOR |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate (as a percent) |  |  |  | 1.75% |  |  |  |  |  |  |  |  |  |
Non Recourse Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 34 | 168 |  |  |  |  |  |  |  |  |
Non Recourse Debt | Agua Caliente Borrower 1, due 2038 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 0 | 86 |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  | 5.43% |  |  |  |  |  |  |  |  |  |
Non Recourse Debt | Midwest Generation, due 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 0 | 48 |  |  |  |  |  |  |  |  |
Discounts |  |  |  | $ 0 | 1 |  |  |  |  |  |  |  |  |
Interest rate, stated percentage |  |  |  | 4.39% |  |  |  |  |  |  |  |  |  |
Debt Instrument, Unamortized Discount [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total discounts |  |  |  | $ 0 | 1 |  |  |  |  |  |  |  |  |
Non Recourse Debt | Other |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 34 | $ 34 |  |  |  |  |  |  |  |  |

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