Risk Management and Fair Values (Reconciliation Of Changes In The Net Assets (Liabilities) For The Fair Value Of Derivatives Classified As Level 3 In The Fair Value Hierarchy) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
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	$ 375	$ 98	$ 312	$ 197
Unrealized gains from price changes	(96)	3	131	(33)
Unrealized gains on originations		17	7	15
Realized gains on settlements	(61)	(48)	(232)	(109)
Balance as of End of Period	$ 218	$ 70	$ 218	$ 70