Derivatives (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Fuel Contracts [Member]	Jun. 30, 2012 Fuel Contracts [Member]	Jun. 30, 2013 Fuel Contracts [Member]	Jun. 30, 2012 Fuel Contracts [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net			$ (78)	$ (716)	$ (1)	$ (520)
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	146
Derivative, Collateral, Right to Reclaim Cash	49
Derivative, Collateral, Obligation to Return Cash		$ (62)