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		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 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	$ (9)	$ (1)	$ (23)	$ (1)
Balance as of Beginning of Period	52	528	178	312
Unrealized gains from price changes	44	(58)	(71)	228
Unrealized gains on originations		6	1	7
Realized gains on settlements	(4)	(100)	(2)	(171)
Balance as of End of Period	$ 83	$ 375	$ 83	$ 375