Debt 3.75% Convertible Senior Subordinated Notes (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Long-term Debt, Gross	$ 2,346,488,000	$ 2,500,434,000
Debt Instrument, Repurchased Face Amount		150,000,000
Gains (Losses) on Extinguishment of Debt	69,381,000	56,280,000	47,558,000
Current Fiscal Year End Date	--12-31
3.75% Convertible Senior Subordinated Notes Due 2042 [Member]
Debt Instrument, Face Amount			390,000,000
Long-term Debt, Gross	0	390,000,000
Debt Instrument, Repurchased Face Amount	103,000,000
Cash Paid for Debt Repurchased	177,000,000
Debt Conversion, Original Debt, Amount	287,000,000
Debt Conversion, cash paid	304,000,000
Debt Conversion, Converted Instrument, Shares Issued	2,900,000
Gains (Losses) on Extinguishment of Debt	37,000,000		33,000,000
Deferred Finance Costs, Gross	3,000,000
Write Off Of Deferred Debt Issuance Cost	3,000,000
3.75% Convertible Senior Subordinated Notes, due 2025 [Member]
Debt Instrument, Interest Rate, Stated Percentage	3.75%
Convertible Debt, initial conversion rate	37.25
Long-term Debt, Gross	79,972,000	132,408,000
Debt Instrument, Repurchased Face Amount	52,000,000	5,000,000
Cash Paid for Debt Repurchased	134,000,000
Gains (Losses) on Extinguishment of Debt	8,000,000	26,000,000
Debt Instrument, Convertible, Conversion Price	$ 26.84
Percent stock price closes above conversion price for option of conversion	130.00%
Deferred Finance Costs, Gross	9,000,000
Extinguishment of Debt, Amount		180,000,000	257,000,000
Write Off Of Deferred Debt Issuance Cost	$ 1,000,000	$ 2,000,000	$ 4,000,000