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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Fuel
Derivative [Line Items]
(Gain) Loss on Derivative Instruments, Net, Pretax	$ (2)	$ (16)	$ 9	$ (12)
Interest Expense
Derivative [Line Items]
(Gain) Loss on Derivative Instruments, Net, Pretax	7	9	15	19
Cash Flow Hedging \| Fuel \| Fuel derivatives
Derivative [Line Items]
Derivative Instruments, (Gain) Loss Reclassified from Accumulated OCI into Income, Effective Portion, Net	(2)	(16)	9	(12)
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	1	2	3
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	12	12
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	$ 0	$ 2	$ 1	$ 4