Derivative Activities Fuel - Effects of Derivative Instruments Gains and Losses (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended							11 Months Ended		12 Months Ended				11 Months Ended	12 Months Ended		7 Months Ended	11 Months Ended	12 Months Ended		11 Months Ended	12 Months Ended		11 Months Ended		12 Months Ended
	Feb. 12, 2010 Predecessor [Member] Cash Flow Hedging		Feb. 12, 2010 Predecessor [Member] Treasury Lock [Member] Cash Flow Hedging	Feb. 12, 2010 Predecessor [Member] Interest Rate Swap [Member] Interest Expense [Member]	Feb. 12, 2010 Predecessor [Member] Fuel Contracts Cash Flow Hedging	Feb. 12, 2010 Predecessor [Member] Fuel Contracts Fuel Expense Cash Flow Hedging		Dec. 31, 2010 Successor [Member] Cash Flow Hedging		Dec. 31, 2012 Successor [Member] Cash Flow Hedging		Dec. 31, 2011 Successor [Member] Cash Flow Hedging		Dec. 31, 2010 Successor [Member] Treasury Lock [Member] Cash Flow Hedging	Dec. 31, 2012 Successor [Member] Treasury Lock [Member] Cash Flow Hedging	Dec. 31, 2011 Successor [Member] Treasury Lock [Member] Cash Flow Hedging	Jul. 31, 2010 Successor [Member] Interest Rate Swap [Member] Interest Expense [Member]	Dec. 31, 2010 Successor [Member] Interest Rate Swap [Member] Interest Expense [Member]	Dec. 31, 2012 Successor [Member] Interest Rate Swap [Member] Interest Expense [Member]	Dec. 31, 2011 Successor [Member] Interest Rate Swap [Member] Interest Expense [Member]	Dec. 31, 2010 Successor [Member] Fuel Contracts Cash Flow Hedging	Dec. 31, 2012 Successor [Member] Fuel Contracts Cash Flow Hedging	Dec. 31, 2011 Successor [Member] Fuel Contracts Cash Flow Hedging	Dec. 31, 2010 Successor [Member] Fuel Contracts Fuel Expense Cash Flow Hedging		Dec. 31, 2012 Successor [Member] Fuel Contracts Fuel Expense Cash Flow Hedging		Dec. 31, 2011 Successor [Member] Fuel Contracts Fuel Expense Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net			$ (6)	$ 6										$ (13)	$ 0	$ 0		$ 14	$ 0	$ 0
Amount of Gain or (Loss) Recognized in Other Comprehensive Income (OCI) on Derivatives (Effective Portion)	(79)				(79)			93		7		50									93	7	50
Amount of Gain or (Loss) Recognized from AOCL into Income (Effective Portion)	(6)					(6)		26		25		98												26		25		98
Amount of Gain or (Loss) Recognized in Income on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing)	(7)	[1]				(7)	[1]	10	[1]	(3)	[1]	(16)	[1]											10	[1]	(3)	[1]	(16)	[1]
Recognized gain on unwind of four interest rate swaps, due 2018																	$ 45

[1] No portion of the gain or (loss) was excluded from the assessment of hedge effectiveness for the periods then ended.