Risk Management and Fair Values (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reconciliation of changes in the net assets (liabilities) for the fair value of derivatives classified as Level 3 in the fair value hierarchy
Balance as of Beginning of period	$ 197	$ 200	$ 207
Unrealized gains from price changes	268	221	310
Unrealized gains/(losses) on originations	15	(4)	5
Realized gains on settlements	(168)	(220)	(322)
Balance as of December 31	$ 312	$ 197	$ 200