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Derivative Activities Derivative Narrative (Details) (USD $)
In Millions, unless otherwise specified
 11 Months Ended 12 Months Ended 1 Months Ended
Dec. 31, 2011
Successor [Member]
gal
Dec. 31, 2010
Successor [Member]
Cost of Fuel [Member]
Operating Expense [Member]
Dec. 31, 2012
Successor [Member]
Cost of Fuel [Member]
Operating Expense [Member]
Dec. 31, 2011
Successor [Member]
Cost of Fuel [Member]
Operating Expense [Member]
Feb. 12, 2010
Predecessor [Member]
Cost of Fuel [Member]
Operating Expense [Member]
Dec. 31, 2011
Fuel Contracts
Designated as Hedging Instrument [Member]
Successor [Member]
Dec. 31, 2012
Interest Rate Swap [Member]
Designated as Hedging Instrument [Member]
Successor [Member]
Dec. 31, 2011
Interest Rate Swap [Member]
Designated as Hedging Instrument [Member]
Successor [Member]
Dec. 31, 2010
Interest Rate Swap [Member]
Designated as Hedging Instrument [Member]
Successor [Member]
Concentration Risk [Line Items]                  
Fuel cost percentage of total operating costs   24.00% 30.00% 30.00% 25.00%        
Number of Gallons of Fuel Covered by Fuel-derivative Agreements 36,000,000                
Maximum Potential Future Exposure on Credit Risk Derivatives           $ 24      
Outstanding interest rate swaps             $ 0 $ 0 $ 0