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Fair Value Measurements (Schedule Of Carrying Values And Estimated Fair Values Of Debt Instruments) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2020 | Sep. 30, 2020 | Sep. 30, 2019 | Aug. 11, 2020 | Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Letters of credit outstanding, amount | $ 123.1 | $ 123.1 |  |  |
Write-off of unamortized debt discounts, premiums and issuance costs | 447.9 | 447.9 | $ 0.0 |  |
Debt Instrument, Convertible, Carrying Amount of Equity Component | 220.0 | 220.0 |  |  |
Revolving Credit Facility |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Letters of credit outstanding, amount | $ 41.2 | $ 41.2 |  |  |
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 | 687.50% | 687.50% |  |  |
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 | 470.00% | 470.00% |  |  |
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 | 487.50% | 487.50% |  |  |
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 | 300.00% | 300.00% |  |  |
Write-off of unamortized debt discounts, premiums and issuance costs |  | $ 128.8 |  |  |
Debt Instrument, Unamortized Discount |  |  |  | $ 119.5 |
Debt Issuance Costs, Net | $ 9.3 | $ 9.3 |  |  |
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 | 450.00% | 450.00% |  |  |
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 | 475.00% | 475.00% |  |  |
4.75% Senior Notes Due 2024 [Member] | Senior Notes |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt instrument interest rate stated percentage | 4.75% | 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 | 800.00% | 800.00% |  |  |
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 | 520.00% | 520.00% |  |  |
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 | 737.50% | 737.50% |  |  |
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 | 775.00% | 775.00% |  |  |
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 | 720.00% | 720.00% |  |  |
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 | 787.50% | 787.50% |  |  |
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 | 540.00% | 540.00% |  |  |
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 | 575.00% | 575.00% |  |  |
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 | 585.00% | 585.00% |  |  |
5.85% Senior Notes Due 2044 [Member] | Senior Notes |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt instrument interest rate stated percentage | 5.85% | 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 |  |  | $ 6,048.3
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 |  |  | 0.0
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 |  |  | 124.8
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 |  |  | 113.2
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 |  |  | 599.2
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 |  |  | 699.0
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 |  |  | 302.0
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 |  |  | 276.5
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 |  |  | 295.7
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 |  |  | 331.7
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 |  |  | 329.2
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 |  |  | 987.1
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 |  |  | 111.7
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 |  |  | 373.3
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 |  |  | 262.8
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 |  |  | 973.3
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 |  |  | 268.8
Estimate of Fair Value Measurement [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Estimated Fair Value | 1,023.4 | 1,023.4 |  |  | 3,874.1
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 |  |  | 0.0
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 | 8.7 | 8.7 |  |  | 117.3
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 | 4.6 | 4.6 |  |  | 95.5
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 | 37.2 | 37.2 |  |  | 460.5
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 | 110.4 | 110.4 |  |  | 607.4
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 | 13.1 | 13.1 |  |  | 167.2
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 | 19.5 | 19.5 |  |  | 201.4
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 | 14.0 | 14.0 |  |  | 181.7
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 | 15.4 | 15.4 |  |  | 186.7
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 | 29.8 | 29.8 |  |  | 218.6
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 | 49.4 | 49.4 |  |  | 575.1
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 | 12.9 | 12.9 |  |  | 70.0
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 | 17.3 | 17.3 |  |  | 153.5
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 | 32.0 | 32.0 |  |  | 194.4
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 | 53.0 | 53.0 |  |  | 450.0
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 | $ 25.1 | $ 25.1 |  |  | $ 194.8

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