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Debt (Schedule Of Long-Term Debt Instruments) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Dec. 31, 2013 | Dec. 31, 2011 | Dec. 31, 2020 | Dec. 31, 2017 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2019 | Mar. 31, 2018
Fair Value Measurement [Domain] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Liabilities Subject to Compromise |  |  | $ 940.8 |  |  |  |  |
Liabilities Subject to Compromise |  |  | 7,313.7 |  |  |  | $ 0.0 |
Current maturities of long-term debt |  |  | 0.0 |  |  |  | 124.8 |
Long-term Debt, Excluding Current Maturities |  |  | 0.0 |  |  |  | $ 5,923.5 |
Write-off of unamortized debt discounts, premiums and issuance costs |  |  | 447.9 |  |  |  |  |
Letters of Credit Outstanding, Amount |  |  | 115.1 |  |  |  |  |
Revolving Credit Facility [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Letters of Credit Outstanding, Amount |  |  | $ 27.0 |  |  |  |  |
6.875% Senior notes due 2020 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 6.875% |  |  |  |  |
6.875% Senior notes due 2020 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage | 6.875% |  |  |  |  |  |  |
Senior Note Maturity Year | 2020 |  |  |  |  |  |  |
4.70% Senior notes due 2021 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 4.70% |  |  |  |  |
4.70% Senior notes due 2021 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  | 4.70% |  |  |  |  |  |
Senior Note Maturity Year |  | 2021 |  |  |  |  |  |
4.875%SeniorNotesDue2022Member [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 4.875% |  |  |  |  |
4.875%SeniorNotesDue2022Member [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 4.875% |  |  |  |  |
3.00% Exchangeable senior notes due 2024 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 3.00% |  |  |  |  |
4.50% Senior notes due 2024 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 4.50% |  |  |  |  |
4.50% Senior notes due 2024 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  |  |  |  | 4.50% |  |
Senior Note Maturity Year |  |  |  |  |  | 2024 |  |
4.75%SeniorNotesDue2024Member [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 4.75% |  |  |  |  |
4.75%SeniorNotesDue2024Member [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 4.75% |  |  |  |  |
8.00% Senior notes due 2024 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 8.00% |  |  |  |  |
8.00% Senior notes due 2024 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  |  | 8.00% |  |  |  |
Senior Note Maturity Year |  |  |  | 2024 |  |  |  |
5.20% Senior notes due 2025 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 5.20% |  |  |  |  |
5.20% Senior notes due 2025 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  |  |  | 5.20% |  |  |
Senior Note Maturity Year |  |  |  |  | 2025 |  |  |
7.38%SeniorNotesDue2025 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 7.375% |  |  |  |  |
7.38%SeniorNotesDue2025 [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 7.375% |  |  |  |  |
7.75% Senior notes due 2026 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 7.75% |  |  |  |  |
7.75% Senior notes due 2026 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  |  |  |  |  |  | 7.75%
7.20% Senior notes due 2027 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 7.20% |  |  |  |  |
7.20% Senior notes due 2027 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  |  |  |  |  | 7.20% |
7.875% Senior notes due 2040 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 7.875% |  |  |  |  |
5.40%SeniorNotesDue2042 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 5.40% |  |  |  |  |
5.75% Senior notes due 2044 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 5.75% |  |  |  |  |
5.75% Senior notes due 2044 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  |  |  | 5.75% | 5.75% |  |
Senior Note Maturity Year |  |  |  |  | 2044 | 2044 |  |
5.85%SeniorNotesDue2044 [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 5.85% |  |  |  |  |
5.85%SeniorNotesDue2044 [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 5.85% |  |  |  |  |
Three percent exchangeable senior notes due twenty twenty four [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Write-off of unamortized debt discounts, premiums and issuance costs |  |  | $ 128.8 |  |  |  |  |
Debt Instrument, Unamortized Discount |  |  | 119.5 |  |  |  |  |
Debt Issuance Costs, Net |  |  | 9.3 |  |  |  |  |
Reported Value Measurement [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 7,096.3 |  |  |  | $ 6,048.3 |
Liabilities Subject to Compromise |  |  | 7,096.3 |  |  |  |  |
Long-term Debt, Excluding Current Maturities |  |  | 0.0 |  |  |  | 5,923.5 |
Reported Value Measurement [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Liabilities Subject to Compromise |  |  | 6,500.0 |  |  |  |  |
Reported Value Measurement [Member] | 6.875% Senior notes due 2020 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 122.9 |  |  |  | 124.8 |
Reported Value Measurement [Member] | 4.70% Senior notes due 2021 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 100.7 |  |  |  | 113.2 |
Reported Value Measurement [Member] | 4.875%SeniorNotesDue2022Member [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 620.8 |  |  |  | 599.2 |
Reported Value Measurement [Member] | 3.00% Exchangeable senior notes due 2024 | Convertible Debt [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 849.5 |  |  |  | 699.0 |
Reported Value Measurement [Member] | 4.50% Senior notes due 2024 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 303.4 |  |  |  | 302.0 |
Reported Value Measurement [Member] | 4.75%SeniorNotesDue2024Member [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 318.6 |  |  |  | 276.5 |
Reported Value Measurement [Member] | 8.00% Senior notes due 2024 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 292.3 |  |  |  | 295.7 |
Reported Value Measurement [Member] | 5.20% Senior notes due 2025 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 333.7 |  |  |  | 331.7 |
Reported Value Measurement [Member] | 7.38%SeniorNotesDue2025 [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 360.8 |  |  |  | 329.2 |
Reported Value Measurement [Member] | 7.75% Senior notes due 2026 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 1,000.0 |  |  |  | 987.1 |
Reported Value Measurement [Member] | 7.20% Senior notes due 2027 | Debentures Due 2027 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 112.1 |  |  |  | 111.7 |
Reported Value Measurement [Member] | 7.875% Senior notes due 2040 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 300.0 |  |  |  | 373.3 |
Reported Value Measurement [Member] | 5.40%SeniorNotesDue2042 [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 400.0 |  |  |  | 262.8 |
Reported Value Measurement [Member] | 5.75% Senior notes due 2044 | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 1,000.5 |  |  |  | 973.3 |
Reported Value Measurement [Member] | 5.85%SeniorNotesDue2044 [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 400.0 |  |  |  | $ 268.8 |
Reported Value Measurement [Member] | Line of Credit [Member] | Line of Credit [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | 581.0 |  |  |  |  |
Reported Value Measurement [Member] | Three percent exchangeable senior notes due twenty twenty four [Member] | Convertible Debt [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt |  |  | $ 849.5 |  |  |  |  |

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