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Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ 1,018	$ 956
Interest Expense	(32)	(29)
Less: Tax Expense	(139)	$ (193)
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net of Tax	5
Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Less: Tax Expense	1
Net of Tax	3
Interest rate derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Less: Tax Expense	0
Net of Tax	2
Fuel derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Reclassification to earnings	4
Interest rate derivatives
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Reclassification to earnings	$ 2

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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
-Paragraph 2
-Subparagraph (SX 210.5-03.2(a),(d))
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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

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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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