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Fair Value Measurements (Schedule Of Carrying Values And Estimated Fair Values Of Debt Instruments) (Details) - USD ($) $ in Millions | Mar. 31, 2021 | Dec. 31, 2020 | Mar. 31, 2020
--- | --- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities Subject to Compromise | $ 7,313.7 | $ 7,313.7 | $ 7,313.7
Debt Instrument, Convertible, Carrying Amount of Equity Component | 220.0 |  |
Letters of credit outstanding, amount | 116.6 |  |
Revolving Credit Facility |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Letters of credit outstanding, amount | $ 26.0 | 27.0 |
6.875% Senior Notes, Due August 15, 2020 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 6.875% |  |
Four Point Seven Zero Percent Senior Notes Member |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 4.70% |  |
4.875% Senior Notes Due 2022 Member [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 4.875% |  |
Three percent exchangeable senior notes due twenty twenty four [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 3.00% |  |
Four Point Five Percent Senior Notes Member [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 4.50% |  |
4.75% Senior Notes Due 2024 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 4.75% |  |
8.00% senior notes due 2024 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 8.00% |  |
Five Point Two Percent Senior Notes [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 5.20% |  |
7.38% Senior Notes Due 2025 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 7.375% |  |
Seven Point Seven Five Percent Senior Notes Due Two Thousand Twenty Six [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 7.75% |  |
Seven Point Two Zero Percent Debentures Member |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 7.20% |  |
Seven Point Eight Seven Five Percent Senior Notes Member |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 7.875% |  |
5.40% Senior Notes Due 2042 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 5.40% |  |
5.75% Senior notes due 2044 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 5.75% |  |
5.85% Senior Notes Due 2044 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Debt instrument interest rate stated percentage | 5.85% |  |
Reported Value Measurement [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | $ 7,096.3 | 7,096.3 |
Liabilities Subject to Compromise | 7,096.3 | 7,096.3 |
LONG-TERM DEBT | 0.0 | 0.0 |
Reported Value Measurement [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities Subject to Compromise | 6,500.0 | 6,500.0 |
Reported Value Measurement [Member] | Line of Credit |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 581.0 | 581.0 |
Reported Value Measurement [Member] | 6.875% Senior Notes, Due August 15, 2020 | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 122.9 | 122.9 |
Reported Value Measurement [Member] | Four Point Seven Zero Percent Senior Notes Member | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 100.7 | 100.7 |
Reported Value Measurement [Member] | 4.875% Senior Notes Due 2022 Member [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 620.8 | 620.8 |
Reported Value Measurement [Member] | Three percent exchangeable senior notes due twenty twenty four [Member] | Convertible Debt [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 849.5 | 849.5 |
Reported Value Measurement [Member] | Four Point Five Percent Senior Notes Member [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 303.4 | 303.4 |
Reported Value Measurement [Member] | 4.75% Senior Notes Due 2024 [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 318.6 | 318.6 |
Reported Value Measurement [Member] | 8.00% senior notes due 2024 [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 292.3 | 292.3 |
Reported Value Measurement [Member] | Five Point Two Percent Senior Notes [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 333.7 | 333.7 |
Reported Value Measurement [Member] | 7.38% Senior Notes Due 2025 [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 360.8 | 360.8 |
Reported Value Measurement [Member] | Seven Point Seven Five Percent Senior Notes Due Two Thousand Twenty Six [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 1,000.0 | 1,000.0 |
Reported Value Measurement [Member] | Seven Point Two Zero Percent Debentures Member | Debentures Due2027 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 112.1 | 112.1 |
Reported Value Measurement [Member] | Seven Point Eight Seven Five Percent Senior Notes Member | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 300.0 | 300.0 |
Reported Value Measurement [Member] | 5.40% Senior Notes Due 2042 [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 400.0 | 400.0 |
Reported Value Measurement [Member] | 5.75% Senior notes due 2044 | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 1,000.5 | 1,000.5 |
Reported Value Measurement [Member] | 5.85% Senior Notes Due 2044 [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term Debt | 400.0 | 400.0 |
Estimate of Fair Value Measurement [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 1,418.1 | 940.8 |
Liabilities Subject to Compromise | 1,418.1 | 940.8 |
Long-term Debt, Fair Value | 0.0 | 0.0 |
Estimate of Fair Value Measurement [Member] | Line of Credit |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 581.0 | 581.0 |
Estimate of Fair Value Measurement [Member] | 6.875% Senior Notes, Due August 15, 2020 | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 20.8 | 8.6 |
Estimate of Fair Value Measurement [Member] | Four Point Seven Zero Percent Senior Notes Member | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 12.5 | 4.5 |
Estimate of Fair Value Measurement [Member] | 4.875% Senior Notes Due 2022 Member [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 81.3 | 32.9 |
Estimate of Fair Value Measurement [Member] | Three percent exchangeable senior notes due twenty twenty four [Member] | Convertible Debt [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 101.9 | 76.5 |
Estimate of Fair Value Measurement [Member] | Four Point Five Percent Senior Notes Member [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 36.7 | 13.7 |
Estimate of Fair Value Measurement [Member] | 4.75% Senior Notes Due 2024 [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 43.6 | 18.8 |
Estimate of Fair Value Measurement [Member] | 8.00% senior notes due 2024 [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 58.8 | 12.9 |
Estimate of Fair Value Measurement [Member] | Five Point Two Percent Senior Notes [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 38.0 | 12.7 |
Estimate of Fair Value Measurement [Member] | 7.38% Senior Notes Due 2025 [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 49.8 | 20.9 |
Estimate of Fair Value Measurement [Member] | Seven Point Seven Five Percent Senior Notes Due Two Thousand Twenty Six [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 111.0 | 44.0 |
Estimate of Fair Value Measurement [Member] | Seven Point Two Zero Percent Debentures Member | Debentures Due2027 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 14.2 | 5.7 |
Estimate of Fair Value Measurement [Member] | Seven Point Eight Seven Five Percent Senior Notes Member | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 54.0 | 21.0 |
Estimate of Fair Value Measurement [Member] | 5.40% Senior Notes Due 2042 [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 53.2 | 23.6 |
Estimate of Fair Value Measurement [Member] | 5.75% Senior notes due 2044 | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | 108.1 | 38.0 |
Estimate of Fair Value Measurement [Member] | 5.85% Senior Notes Due 2044 [Member] | Senior Notes |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Estimated Fair Value | $ 53.2 | $ 26.0 |

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