Debt And Interest Expense (Convertible Debentures) (Narrative) (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	1 Months Ended	12 Months Ended
	Aug. 31, 2007 Rate	Dec. 31, 2014 Rate	Dec. 31, 2013	Apr. 16, 2013 Rate	Aug. 15, 2007 Rate
Debt Disclosure [Abstract]
Principal amount of debt		$ 1,250,000,000	$ 1,250,000,000	$ 750,000,000	$ 1,250,000,000
Convertible debenture, interest rate	3.25%			4.625%	3.25%
Convertible debenture, maturity date	Aug. 15, 2037
Conversion rate per 1000 principal amount	29.0968
Denominator of principal value upon which conversion is based	1,000
Conversion price					$ 34.37
stock reserved for issuance			36.4
Minimum required sales price as a percentage of conversion price	150.00%
Conversion threshold minimum stock price as a percentage of conversion price	130.00%
Debt Instrument, Convertible, Stock Price Trigger	$ 44.68
Percentage of maximum required trading price per convertible debentures	98.00%
Latest conversion date	May 15, 2037
Additional common shares potentially issuable based on if-converted value of convertible debentures		14.4
Purchase price as percentage of principal amount of convertible debt	100.00%
Debt issuance costs	$ 25,777,000
Discount rate	8.50%	8.50%
Debt Instrument, Convertible, Remaining Discount Amortization Period		22 years 227 days
Effective interest rate					8.39%