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v3.19.3.a.u2

Debt - Public Debt (Details) |  | 1 Months Ended | 2 Months Ended | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | ---
Oct. 02, 2017 shares | Sep. 30, 2014 shares | May 31, 2017 USD ($) $ / shares | Jun. 30, 2017 USD ($) cash_tender_offer $ / shares shares | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Oct. 15, 2019 USD ($) | Mar. 31, 2018 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Interest charge related to early redemption of notes |  |  |  | $ 58,000,000 |  | $ 19,000,000 |  |  |
Cash paid to holders of debt instrument, net |  |  |  | $ 409,000,000 |  |  |  |  |
Common stock sold (in shares) | shares | 24,022 | 25,000,000 |  | 12,958,767 |  |  |  |  |
Common stock sold per share (usd per share) | $ / shares |  |  |  | $ 35.91 |  |  |  |  |
Debt instrument, repurchase amount |  |  |  | $ 874,000,000 |  |  |  |  |
Interest paid |  |  |  | 27,000,000 |  |  |  |  |
Legal fees |  |  |  | 2,000,000 |  |  |  |  |
Pre-tax gain on sale of common stock |  |  |  | 167,000,000 |  |  | $ 167,000,000 |  |
Interest expense |  |  |  | 24,000,000 | $ 338,000,000 | $ 378,000,000 | $ 496,000,000 |  |
Interest Rate Swap |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Proceeds from interest received |  |  |  | 8,000,000 |  |  |  |  |
Investment Banks |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  | $ 805,000,000 |  |  |  |  |
Number of cash tender offers | cash_tender_offer |  |  |  | 3 |  |  |  |  |
Common stock sold per share (usd per share) | $ / shares |  |  | $ 35.91 |  |  |  |  |  |
Pre-tax gain on sale of common stock |  |  | $ 167,000,000 |  |  |  |  |  |
Investment Banks | Maximum |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  | $ 1,000,000,000 |  |  |  |  |
1.63% Convertible Notes, due 2019 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Convertible notes, interest rate percentage |  |  |  |  | 1.63% |  |  | 1.63% |
Debt instrument, repurchase amount |  |  |  |  |  |  |  | $ 403,000,000 |
6.150% Notes, due 2020 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Convertible notes, interest rate percentage |  |  |  |  | 6.15% |  |  |  |
5.40% Notes, due 2021 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Convertible notes, interest rate percentage |  |  |  |  | 5.40% |  |  |  |
5.87% Notes, due 2022 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Convertible notes, interest rate percentage |  |  |  |  | 5.87% |  |  |  |
5.125% Notes, due 2024 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Convertible notes, interest rate percentage |  |  |  |  | 5.125% |  |  |  |
5.90% Notes, due 2027 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Convertible notes, interest rate percentage |  |  |  |  | 5.90% |  |  |  |
6.75% Bonds, due 2028 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Convertible notes, interest rate percentage |  |  |  |  | 6.75% |  |  |  |
5.95% Notes due 2037 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Convertible notes, interest rate percentage |  |  |  |  | 5.95% |  |  |  |
Iowa Finance Authority Loan, due 2042 (4.75%) |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Convertible notes, interest rate percentage |  |  |  |  | 4.75% |  |  |  |
5.72% Notes due 2019 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Convertible notes, interest rate percentage |  |  |  |  | 5.72% | 5.72% | 5.72% |  | 5.72%
Debt instrument, face amount |  |  |  |  |  |  |  |  | $ 500,000,000
Debt instrument redemption amount |  |  |  |  |  |  |  |  | $ 518,000,000
5.72% Notes due 2019 | Investment Banks |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  | $ 250,000,000 |  |  |  |  |
6.5% Bonds due 2018 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Convertible notes, interest rate percentage |  |  |  | 6.50% |  | 6.50% |  |  |
Debt instrument, face amount |  |  |  | $ 100,000,000 |  |  |  |  |
6.5% Bonds due 2018 | Investment Banks |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  | $ 150,000,000 |  |  |  |  |
6.75% Notes due 2018 |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Convertible notes, interest rate percentage |  |  |  | 6.75% |  | 6.75% | 6.75% |  |
Debt instrument, face amount |  |  |  | $ 345,000,000 |  |  |  |  |
Debt instrument redemption amount |  |  |  | 479,000,000 |  |  |  |  |
6.75% Notes due 2018 | Investment Banks |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  | $ 405,000,000 |  |  |  |  |

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