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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		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2011	Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2018
Fair Value Measurement [Domain]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Liabilities Subject to Compromise						$ 940.8
Current maturities of long-term debt						0.0	$ 124.8
Long-term Debt, Excluding Current Maturities						0.0	5,923.5
Liabilities Subject to Compromise						7,313.7	0.0
Debt Instrument, Convertible, Carrying Amount of Equity Component						$ 220.0
6.875% Senior notes due 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						6.875%
6.875% Senior notes due 2020 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage	6.875%
Senior Note Maturity Year	2020
4.70% Senior notes due 2021
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						4.70%
4.70% Senior notes due 2021 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage		4.70%
Senior Note Maturity Year		2021
4.875%SeniorNotesDue2022Member [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						4.875%
4.875%SeniorNotesDue2022Member [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						4.875%
3.00% Exchangeable senior notes due 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						3.00%
3.00% Exchangeable senior notes due 2024 | Convertible Debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt Instrument, Convertible, Carrying Amount of Equity Component						$ 220.0	$ 220.0
4.50% Senior notes due 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						4.50%
4.50% Senior notes due 2024 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage					4.50%
Senior Note Maturity Year					2024
4.75%SeniorNotesDue2024Member [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						4.75%
4.75%SeniorNotesDue2024Member [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						4.75%
8.00% Senior notes due 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						8.00%
8.00% Senior notes due 2024 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage			8.00%
Senior Note Maturity Year			2024
5.20% Senior notes due 2025
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						5.20%
5.20% Senior notes due 2025 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage				5.20%
Senior Note Maturity Year				2025
7.38%SeniorNotesDue2025 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						7.375%
7.38%SeniorNotesDue2025 [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						7.375%
7.75% Senior notes due 2026
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						7.75%
7.75% Senior notes due 2026 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage								7.75%
7.20% Senior notes due 2027
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						7.20%
7.20% Senior notes due 2027 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage							7.20%
7.875% Senior notes due 2040
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						7.875%
5.40%SeniorNotesDue2042 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						5.40%
5.75% Senior notes due 2044
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						5.75%
5.75% Senior notes due 2044 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage				5.75%	5.75%
Senior Note Maturity Year				2044	2044
5.85%SeniorNotesDue2044 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						5.85%
5.85%SeniorNotesDue2044 [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage						5.85%
Reported Value Measurement [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						$ 7,096.3	$ 6,048.3
Long-term Debt, Excluding Current Maturities						0.0	5,923.5
Liabilities Subject to Compromise						7,096.3
Reported Value Measurement [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Liabilities Subject to Compromise						6,500.0
Reported Value Measurement [Member] | 6.875% Senior notes due 2020 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						122.9	124.8
Reported Value Measurement [Member] | 4.70% Senior notes due 2021 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						100.7	113.2
Reported Value Measurement [Member] | 4.875%SeniorNotesDue2022Member [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						620.8	599.2
Reported Value Measurement [Member] | 3.00% Exchangeable senior notes due 2024 | Convertible Debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						849.5	699.0
Reported Value Measurement [Member] | 4.50% Senior notes due 2024 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						303.4	302.0
Reported Value Measurement [Member] | 4.75%SeniorNotesDue2024Member [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						318.6	276.5
Reported Value Measurement [Member] | 8.00% Senior notes due 2024 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						292.3	295.7
Reported Value Measurement [Member] | 5.20% Senior notes due 2025 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						333.7	331.7
Reported Value Measurement [Member] | 7.38%SeniorNotesDue2025 [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						360.8	329.2
Reported Value Measurement [Member] | 7.75% Senior notes due 2026 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						1,000.0	987.1
Reported Value Measurement [Member] | 7.20% Senior notes due 2027 | Debentures Due 2027
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						112.1	111.7
Reported Value Measurement [Member] | 7.875% Senior notes due 2040 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						300.0	373.3
Reported Value Measurement [Member] | 5.40%SeniorNotesDue2042 [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						400.0	262.8
Reported Value Measurement [Member] | 5.75% Senior notes due 2044 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						1,000.5	973.3
Reported Value Measurement [Member] | 5.85%SeniorNotesDue2044 [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt						400.0	268.8
Estimate of Fair Value Measurement [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						940.8	3,874.1
Current maturities of long-term debt						0.0	0.0
Long-term Debt, Fair Value						0.0	3,874.1
Estimate of Fair Value Measurement [Member] | Line of Credit [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						581.0
Estimate of Fair Value Measurement [Member] | 6.875% Senior notes due 2020 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						8.6	117.3
Estimate of Fair Value Measurement [Member] | 4.70% Senior notes due 2021 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						4.5	95.5
Estimate of Fair Value Measurement [Member] | 4.875%SeniorNotesDue2022Member [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						32.9	460.5
Estimate of Fair Value Measurement [Member] | 3.00% Exchangeable senior notes due 2024 | Convertible Debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						76.5	607.4
Estimate of Fair Value Measurement [Member] | 4.50% Senior notes due 2024 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						13.7	167.2
Estimate of Fair Value Measurement [Member] | 4.75%SeniorNotesDue2024Member [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						18.8	201.4
Estimate of Fair Value Measurement [Member] | 8.00% Senior notes due 2024 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						12.9	181.7
Estimate of Fair Value Measurement [Member] | 5.20% Senior notes due 2025 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						12.7	186.7
Estimate of Fair Value Measurement [Member] | 7.38%SeniorNotesDue2025 [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						20.9	218.6
Estimate of Fair Value Measurement [Member] | 7.75% Senior notes due 2026 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						44.0	575.1
Estimate of Fair Value Measurement [Member] | 7.20% Senior notes due 2027 | Debentures Due 2027
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						5.7	70.0
Estimate of Fair Value Measurement [Member] | 7.875% Senior notes due 2040 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						21.0	153.5
Estimate of Fair Value Measurement [Member] | 5.40%SeniorNotesDue2042 [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						23.6	194.4
Estimate of Fair Value Measurement [Member] | 5.75% Senior notes due 2044 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						38.0	450.0
Estimate of Fair Value Measurement [Member] | 5.85%SeniorNotesDue2044 [Member] | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure						$ 26.0	$ 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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