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
	Mar. 31, 2013	Mar. 31, 2012
Reconciliation of changes in the net assets (liabilities) for the fair value of derivatives classified as Level 3 in the fair value hierarchy
Realized Gains Losses Due To Ineffectiveness	$ (14)
Balance as of Beginning of Period	178	312
Unrealized gains from price changes	(115)	286
Unrealized gains on originations	1	1
Realized gains on settlements	2	(71)
Balance as of End of Period	$ 52	$ 528