Financial Derivative Instruments Narrative (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended	3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended				3 Months Ended				6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Fuel derivatives	Jun. 30, 2014 Fuel derivatives	Jun. 30, 2014 Cash Flow Hedging		Jun. 30, 2013 Cash Flow Hedging		Jun. 30, 2014 Cash Flow Hedging		Jun. 30, 2013 Cash Flow Hedging		Jun. 30, 2014 Cash Flow Hedging Fuel derivatives		Jun. 30, 2013 Cash Flow Hedging Fuel derivatives		Jun. 30, 2014 Cash Flow Hedging Fuel derivatives		Jun. 30, 2013 Cash Flow Hedging Fuel derivatives		Jun. 30, 2014 Cash Flow Hedging Interest rate derivatives		Jun. 30, 2013 Cash Flow Hedging Interest rate derivatives		Jun. 30, 2014 Cash Flow Hedging Interest rate derivatives		Jun. 30, 2013 Cash Flow Hedging Interest rate derivatives		Jun. 30, 2014 Remainder of 2014	Jun. 30, 2014 Other Noncurrent Liabilities Interest rate derivatives	Dec. 31, 2013 Other Noncurrent Liabilities Interest rate derivatives
Derivative [Line Items]
GainLossOnDerivativeNetDueToLossOfHedgeAccounting					$ 15	$ 20
Percent of fuel consumption hedged	33.00%		33.00%																												41.00%
Cash collateral deposits provided to counterparty - noncurrent																																32	32
Premiums paid for fuel derivative contracts	17	12	34	17
Current Unrealized Net Gains (Losses) in OCI	(12)		(12)
Cumulative ineffectiveness recognized for unsettled hedges	99
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net							(2)	[1]	(41)	[1]	(6)	[1]	(72)	[1]	1	[1],[2]	(37)	[1],[2]	1	[1],[2]	(63)	[1],[2]	(3)	[1],[2]	(4)	[1],[2]	(7)	[1],[2]	(9)	[1],[2]
Maximum sum of derivatives of counterparty to be included in other (less than $20 million)	$ 20		$ 20
Cash collateral provided as a percentage of derivative contract value (in hundredths)	100.00%		100.00%

[1] Amounts related to fuel derivative contracts and interest rate derivatives are included in Fuel and oil and Interest expense, respectively.

[2] Net of tax