Fair Value Of Financial Instruments (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative positions, at fair value	$ 1,566,000,000	$ 4,037,000,000
Debt instrument, interest rate, stated percentage	3.75%	3.75%	3.75%
Financial instrument resale and repurchase agreements at contract value	3,745,000,000	3,441,000,000
Resale and repurchase agreements maturities, days	30
3.75% Convertible Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, interest rate, stated percentage	3.75%
2013 Convertible Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt utilizing discounted cash flow analyses	$ 2,300,000,000	$ 2,400,000,000