Assets And Liabilities Measured At Fair Value Realized Unrealized Gain Loss (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Realized and unrealized gains (losses) on financial instruments, net (note 7)	$ (57)	$ (22)	$ (351)
Fair Value Option Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Realized and unrealized gains (losses) on financial instruments, net (note 7)	173	514	470
Exchangeable Senior Debentures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Realized and unrealized gains (losses) on financial instruments, net (note 7)	(230)	(553)	(602)
Other Financial Instruments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Realized and unrealized gains (losses) on financial instruments, net (note 7)		$ 17	$ (219)