Debt Senior Unsecured Notes (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Mar. 31, 2015 |
Sep. 30, 2014 |
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| Debt Instrument [Line Items] | ||||||||||
| Long-term Debt | $ 11,857 | $ 11,857 | $ 10,156 | |||||||
| Debt Instrument, Interest Rate, Effective Percentage | 5.80% | 5.80% | 5.70% | |||||||
| Debt Issuance Costs, Net | $ 114 | $ 114 | ||||||||
| Gains (Losses) on Extinguishment of Debt | (58) | $ 28 | $ (38) | |||||||
| Senior Unsecured Notes 2023 [Member] | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Long-term Debt | [1] | $ 623 | $ 623 | $ 1,227 | ||||||
| Debt Instrument, Interest Rate, Effective Percentage | [2] | 5.70% | 5.70% | 5.60% | ||||||
| Debt Instrument, Face Amount | $ 1,250 | |||||||||
| Debt Instrument, Interest Rate, Stated Percentage | 5.375% | |||||||||
| Gains (Losses) on Extinguishment of Debt | $ 24 | $ 0 | $ 1 | |||||||
| Senior Unsecured Notes 2024 [Member] | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Long-term Debt | $ 479 | $ 479 | $ 599 | |||||||
| Debt Instrument, Interest Rate, Effective Percentage | [2] | 5.70% | 5.70% | 5.70% | ||||||
| Debt Instrument, Face Amount | $ 650 | |||||||||
| Debt Instrument, Interest Rate, Stated Percentage | 5.50% | |||||||||
| Gains (Losses) on Extinguishment of Debt | $ (1) | $ 4 | ||||||||
| Senior Unsecured Notes 2025 [Member] | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Long-term Debt | $ 1,174 | $ 1,174 | $ 1,210 | |||||||
| Debt Instrument, Interest Rate, Effective Percentage | [2] | 5.80% | 5.80% | 6.00% | ||||||
| Debt Instrument, Face Amount | $ 1,550 | |||||||||
| Debt Instrument, Interest Rate, Stated Percentage | 5.75% | |||||||||
| Gains (Losses) on Extinguishment of Debt | $ 3 | $ 30 | ||||||||
| Senior Unsecured Notes 2028 [Member] | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Long-term Debt | [1] | $ 1,387 | $ 1,387 | $ 0 | ||||||
| Debt Instrument, Interest Rate, Effective Percentage | [2] | 5.30% | 5.30% | 0.00% | ||||||
| Debt Instrument, Face Amount | $ 1,400 | $ 1,400 | ||||||||
| Debt Instrument, Interest Rate, Stated Percentage | 5.125% | 5.125% | ||||||||
| Debt Issuance Costs, Net | $ 13 | $ 13 | ||||||||
| Unsecured Debt [Member] | ||||||||||
| Debt Instrument [Line Items] | ||||||||||
| Long-term Debt | $ 3,663 | 3,663 | $ 3,036 | |||||||
| Gains (Losses) on Extinguishment of Debt | $ 2 | $ 35 | ||||||||
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