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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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The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

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