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Fair Value Measurements (Schedule Of Carrying Values And Estimated Fair Values Of Debt Instruments) (Details) - USD ($)
$ in Millions
Sep. 30, 2016
Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Carrying Value $ 4,702.6 $ 5,868.6
Estimated Fair Value $ 3,730.2 $ 4,621.9
Eight Point Five Zero Percent Senior Notes Member    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Instrument, Interest Rate, Stated Percentage 8.50% 8.50%
Carrying Value $ 486.1 $ 566.4
Estimated Fair Value $ 473.0 $ 510.2
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%
Carrying Value $ 739.4 $ 990.9
Estimated Fair Value $ 674.8 $ 850.5
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%
Carrying Value $ 673.9 $ 1,476.7
Estimated Fair Value $ 613.0 $ 1,254.0
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%
Carrying Value $ 618.5 $ 619.7
Estimated Fair Value $ 449.7 $ 417.4
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%
Carrying Value $ 662.6 $ 692.5
Estimated Fair Value $ 505.3 $ 505.2
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%
Carrying Value $ 149.1 $ 149.1
Estimated Fair Value $ 123.4 $ 133.5
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%
Carrying Value $ 378.7 $ 379.8
Estimated Fair Value $ 240.7 $ 244.0
Five Point 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 5.75% 5.75%
Carrying Value $ 994.3 $ 993.5
Estimated Fair Value $ 650.3 $ 707.1