Derivative Instruments and Hedging Activities (Changes in AOCI Related to Derivative Gains (Losses)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Accumulated Other Comprehensive Income [Roll Forward]
Balance of Accumulated Other Comprehensive Income (Loss) at Beginning of Period	$ (57)
Unrealized gains (losses)	(172)
Losses (gains) reclassified to earnings	36
Other comprehensive income (loss), tax, portion attributable to parent	35
Balance of Accumulated Other Comprehensive Income (Loss) at End of period	(158)
Deferred Gain (Loss) On Hedging Activities [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Balance of Accumulated Other Comprehensive Income (Loss) at Beginning of Period	5	4
Unrealized gains (losses)	(128)	9
Losses (gains) reclassified to earnings	31	3
Other comprehensive income (loss), tax, portion attributable to parent	33	(5)
Balance of Accumulated Other Comprehensive Income (Loss) at End of period	$ (59)	$ 11