Fair Value Measurements (Schedule Of Carrying Values And Estimated Fair Values Of Debt Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Jan. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 4,943.5		$ 5,274.5
Estimated Fair Value	4,665.7		5,001.7
8.50% Senior Notes due 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	317.6		480.2
Estimated Fair Value	$ 319.5		$ 485.0
Debt instrument, interest rate, stated percentage	8.50%		8.50%
6.875% Senior Notes due 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 592.8		$ 735.9
Estimated Fair Value	$ 577.0		$ 727.5
Debt instrument, interest rate, stated percentage	6.875%		6.875%
4.70% Senior notes due 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 301.1		$ 674.4
Estimated Fair Value	$ 298.0		$ 658.9
Debt instrument, interest rate, stated percentage	4.70%		4.70%
3.00% Exchangeable senior notes due 2024(1) \| Convertible Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
3.00% exchangeable senior notes, excluding discount and net of debt issuance costs	$ 832.5
Carrying Value	613.5		$ 604.3
Estimated Fair Value	834.6		874.7
4.50% Senior Notes due 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	618.7		618.6
Estimated Fair Value	$ 530.1		$ 536.0
Debt instrument, interest rate, stated percentage	4.50%		4.50%
8.00% Senior notes due 2024 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 338.7		$ 0.0
Estimated Fair Value	$ 335.7		0.0
Debt instrument, interest rate, stated percentage	8.00%
8.00% Senior notes due 2024 [Member] \| Convertible Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument, interest rate, stated percentage		8.00%
5.20% Senior Notes due 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 663.0		662.8
Estimated Fair Value	$ 583.6		$ 582.3
Debt instrument, interest rate, stated percentage	5.20%		5.20%
7.20% Debentures due 2027
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 149.2		$ 149.2
Estimated Fair Value	$ 147.6		$ 138.7
Debt instrument, interest rate, stated percentage	7.20%		7.20%
7.875% Senior notes due 2040
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 377.9		$ 378.3
Estimated Fair Value	$ 278.2		$ 270.6
Debt instrument, interest rate, stated percentage	7.875%		7.875%
5.75% Senior notes due 2044
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 971.0		$ 970.8
Estimated Fair Value	$ 761.4		$ 728.0
Debt instrument, interest rate, stated percentage	5.75%		5.75%

3.00% exchangeable senior notes, excluding discount and net of debt issuance costs

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- Definition

Debt Instrument Carrying Value

+ References

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- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13476-108611

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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+ References

No definition available.

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