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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
		Sep. 30, 2017	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2019	Dec. 31, 2015	Dec. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Current maturities of long-term debt					$ 124.8		$ 0.0
Long-term Debt, Excluding Current Maturities					$ 5,923.5		5,010.4
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%
Senior Note Maturity Year					2020
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	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%
Senior Note Maturity Year					2021
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	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%
Senior Note Maturity Year					2022
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(2)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage					3.00%
Senior Note Maturity Year					2024
3.00% Exchangeable senior notes due 2024(2) | Convertible Debt [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
Carrying value of 2024 convertible notes					$ 838.3		$ 836.3
4.50% Senior notes due 2024(1)
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
4.50% Senior notes due 2024(1) | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage				4.50%		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%
Senior Note Maturity Year					2024
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(1)
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
8.00% Senior notes due 2024(1) | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage				8.00%	8.00%		8.00%
Senior Note Maturity Year					2024
5.20% Senior notes due 2025(1)
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
5.20% Senior notes due 2025(1) | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage				5.20%	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%
Senior Note Maturity Year					2025
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%
Senior Note Maturity Year					2026
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%
Senior Note Maturity Year					2027
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%			7.20%
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%
Senior Note Maturity Year					2040
7.875% Senior notes due 2040 | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage				7.875%
Senior Note Maturity Year				2040
5.40%SeniorNotesDue2042 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, interest rate, stated percentage					5.40%
Senior Note Maturity Year					2042
5.40%SeniorNotesDue2042 [Member] | Senior Notes [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%
Senior Note Maturity Year					2044
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%
Senior Note Maturity Year					2044
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					$ 6,048.3		$ 5,010.4
Long-term Debt, Excluding Current Maturities					5,923.5		5,010.4
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					124.8		127.5
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					113.2		112.7
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					599.2		0.0
Reported Value Measurement [Member] | 3.00% Exchangeable senior notes due 2024(2) | Convertible Debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt					699.0		666.8
Reported Value Measurement [Member] | 4.50% Senior notes due 2024(1) | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt					302.0		619.8
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					276.5		0.0
Reported Value Measurement [Member] | 8.00% Senior notes due 2024(1) | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt					295.7		337.0
Reported Value Measurement [Member] | 5.20% Senior notes due 2025(1) | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-term Debt					331.7		664.4
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					329.2		0.0
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					987.1		985.0
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					111.7		149.3
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					373.3		375.0
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					262.8		0.0
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					973.3		972.9
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					268.8		0.0
Estimate of Fair Value Measurement [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure					3,874.1		3,545.8
Current maturities of long-term debt					0.0		0.0
Long-term Debt, Fair Value					3,874.1		3,545.8
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					117.3		121.6
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					95.5		101.8
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					460.5		0.0
Estimate of Fair Value Measurement [Member] | 3.00% Exchangeable senior notes due 2024(2) | Convertible Debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure	[1]				607.4		575.5
Estimate of Fair Value Measurement [Member] | 4.50% Senior notes due 2024(1) | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure					167.2		405.2
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					201.4		0.0
Estimate of Fair Value Measurement [Member] | 8.00% Senior notes due 2024(1) | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure					181.7		273.7
Estimate of Fair Value Measurement [Member] | 5.20% Senior notes due 2025(1) | Senior Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument, Fair Value Disclosure					186.7		443.9
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					218.6		0.0
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					575.1		725.5
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					70.0		109.1
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					153.5		223.2
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					194.4		0.0
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					450.0		566.3
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					$ 194.8		$ 0.0
[1] Our 2024 Convertible Notes were issued with a conversion feature. The 2024 Convertible Notes were separated into their liability and equity components on our consolidated balance sheet. The equity component was initially recorded to additional paid-in capital and as a debt discount that will be amortized to interest expense over the life of the instrument. Excluding the unamortized discount, the carrying value of the 2024 Convertible Notes was $838.3 million and $836.3 million as of December 31, 2019 and 2018, respectively. See "Note 7 - Debt" for additional information on this issuance.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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