Fair Value Measurements (Schedule Of Carrying Values And Estimated Fair Values Of Debt Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Current Maturities	$ 224.5	$ 124.8
Short-term Debt, Fair Value	0.0	0.0
LONG-TERM DEBT	6,148.6	$ 5,923.5
Long-term Line of Credit	328.9
Unamortized Debt Issuance Expense	6.0
Letters of credit outstanding, amount	117.9
Revolving Credit Facility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Letters of credit outstanding, amount	3.2
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,300.0
7.88% Senior Notes Due 2019 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate stated percentage	7.88%	7.88%
Six Point Eight Seven Five Percent Senior Notes Due Two Thousand Twenty Member
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate stated percentage	6.875%	6.875%
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	4.70%	4.70%
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	4.58%	4.58%
4.875% Senior Notes Due 2022 Member [Member] \| Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate stated percentage	4.875%
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	3.00%	3.00%
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]
3.00% exchangeable senior notes, excluding discount and net of debt issuance costs	$ 839.2	$ 838.3
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	4.50%	4.50%
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	4.75%	4.75%
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%
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	8.00%	8.00%
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	7.38%	7.38%
7.38% Senior Notes Due 2025 [Member] \| Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate stated percentage	7.375%
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	5.20%	5.20%
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	7.75%	7.75%
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	7.20%	7.20%
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	7.875%	7.875%
Seven Point Eight Seven Five Percent Senior Notes Member \| Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate stated percentage	7.875%
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	5.40%	5.40%
5.40% Senior Notes Due 2042 [Member] \| Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate stated percentage	5.40%
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	5.75%	5.75%
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	5.85%	5.85%
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%
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	$ 6,373.1	$ 6,048.3
LONG-TERM DEBT	6,148.6	5,923.5
Reported Value Measurement [Member] \| Line of Credit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	322.9	0.0
Reported Value Measurement [Member] \| Six Point Eight Seven Five Percent Senior Notes Due Two Thousand Twenty Member \| Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	124.1	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	100.4	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	601.2	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	707.7	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	302.0	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	278.6	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	295.5	295.7
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	330.2	329.2
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	331.8	331.7
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	987.7	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	111.7	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	372.8	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	263.2	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	974.2	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	269.1	268.8
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	1,368.2	3,874.1
Long-term Debt, Fair Value	1,368.2	3,874.1
Estimate of Fair Value Measurement [Member] \| Line of Credit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	328.9	0.0
Estimate of Fair Value Measurement [Member] \| Six Point Eight Seven Five Percent Senior Notes Due Two Thousand Twenty Member \| Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	27.8	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	10.4	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	125.9	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	214.3	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	28.6	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	64.2	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	27.6	181.7
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	82.6	218.6
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	33.8	186.7
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	107.7	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	16.6	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	46.9	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	78.8	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	93.5	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	$ 80.6	$ 194.8

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

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- Definition

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

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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- Definition

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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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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

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