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Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ 1,202	$ 1,024	$ 2,220	$ 1,979
Interest Expense	(33)	(27)	(66)	(56)
Less: Tax Expense	(227)	$ (422)	(366)	$ (616)
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	(12)		(7)
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Reclassification to earnings	16		12
Less: Tax Expense	(4)		(3)
Net of Tax	(12)		(9)
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Less: Tax Expense	(1)		(1)
Net of Tax	0		2
Interest rate derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Reclassification to earnings	$ (1)		$ (3)

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[Line Items] for Disclosure of information about items reclassified out of accumulated other comprehensive income (loss).

+ References

No definition available.

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Fuel costs incurred that are directly related to goods produced and sold and services rendered during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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