The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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Financial Derivative Instruments - (Gain) Loss in Income by Hedging Relationship (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fuel
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	$ (20)	$ 151	$ (32)	$ 447
Interest Expense
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	9	7	26	23
Cash Flow Hedging \| Fuel \| Fuel derivatives
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(20)	151	(32)	447
Cash Flow Hedging \| Fuel \| Interest rate derivatives
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	0	0	0
Cash Flow Hedging \| Interest Expense \| Fuel derivatives
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	0	0	0
Cash Flow Hedging \| Interest Expense \| Interest rate derivatives
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	1	2	4	8
Designated as Hedging Instrument \| Fair Value Hedging \| Fuel \| Interest rate derivatives
Derivative [Line Items]
Interest Expense, Debt	0	0	0	0
Designated as Hedging Instrument \| Fair Value Hedging \| Interest Expense \| Interest rate derivatives
Derivative [Line Items]
Interest Expense, Debt	6	6	17	17
Not Designated as Hedging Instrument \| Fair Value Hedging \| Fuel \| Interest rate derivatives
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	0	0	0	0
Not Designated as Hedging Instrument \| Fair Value Hedging \| Interest Expense \| Interest rate derivatives
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	$ 2	$ (1)	$ 5	$ (2)