Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Derivative Financial Instruments, Assets [Member]
Derivative position of company
Total fair value of derivative positions	$ 1,733	$ 1,913
Netting (a)	(304)	(294)
Total	1,429	1,619
Derivative Financial Instruments, Liabilities [Member]
Derivative position of company
Total fair value of derivative positions	2,254	2,554
Netting (a)	(1,798)	(1,889)
Total	$ 456	$ 665