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Debt - Public Debt (Details) - USD ($) $ in Millions |  |  |  |  |  | 3 Months Ended | 6 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | ---
May 03, 2021 | Jan. 15, 2021 | May 21, 2020 | Apr. 24, 2020 | Apr. 06, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Dec. 31, 2020
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Payment for early redemption of debt |  |  |  |  |  |  |  | $ 22 | $ 59 |
Early termination premium |  |  |  |  |  |  |  |  | 35 |
Interest expense |  |  |  |  |  |  |  |  | 17 |
6.150% Notes, due 2020 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Early redemption of debt |  |  |  |  | $ 1,000 |  |  |  |  |
Long-term debt, interest rate |  |  |  |  | 6.15% |  |  |  |  |
Payment for early redemption of debt |  |  |  |  | $ 1,020 |  |  |  |  |
5.400% Notes, due 2021 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Early redemption of debt | $ 476 | $ 361 | $ 589 |  | 300 |  |  |  |  |
Long-term debt, interest rate |  |  |  |  |  |  |  |  |  | 5.40%
Payment for early redemption of debt |  |  |  |  | $ 315 |  |  |  |  |
Interest expense |  |  |  |  |  |  | $ 24 |  |  |
Accrued interest paid |  | $ 5 |  |  |  |  |  |  |  |
6.875% Notes, due 2025 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Early redemption of debt |  |  |  | $ 1,200 |  |  |  |  |  |
Long-term debt, interest rate |  |  |  | 6.875% |  | 6.875% |  | 6.875% |  |
Deferred financing costs |  |  |  |  |  |  | 14 |  | $ 14 |
5.870% Notes, due 2022 |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Early redemption of debt |  |  | $ 151 |  |  |  |  |  |  |
Long-term debt, interest rate |  |  |  |  |  |  |  |  |  | 5.87%
Payment for early redemption of debt | 503 |  |  |  |  |  |  |  |  |
Early termination premium |  |  |  |  |  | $ 23 |  |  |  |
Interest expense |  |  |  |  |  |  | $ 4 |  |  |
Accrued interest paid | 5 |  |  |  |  |  |  |  |  |
5.400% and 5.870% Notes, Redemption |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Increase (decrease) interest expense, net | $ (47) |  |  |  |  |  |  |  |  |

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