Derivative Instruments and Hedging Activities (Changes in AOCI Related to Derivative Gains (Losses)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Accumulated Other Comprehensive Income [Roll Forward]
Balance of Accumulated Other Comprehensive Income at Beginning of Period	$ (638)		$ (450)
Unrealized gains (losses)	227		16
Losses (gains) reclassified to earnings	27		57
Other comprehensive income (loss), tax, portion attributable to parent	(14)		(21)
Balance of Accumulated Other Comprehensive Income at End of period	(398)		(398)
Deferred Gain (Loss) On Hedging Activities [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Balance of Accumulated Other Comprehensive Income at Beginning of Period	6	50	4	30
Unrealized gains (losses)	13	142	15	164
Losses (gains) reclassified to earnings	3	(88)	3	(77)
Other comprehensive income (loss), tax, portion attributable to parent	(7)	(18)	(7)	(31)
Balance of Accumulated Other Comprehensive Income at End of period	$ 15	$ 86	$ 15	$ 86