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Fair Value Measurement - Fair Value Assets and Liabilities Measured on Recurring Basis with Unobservable Inputs (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended
		Sep. 30, 2016	Sep. 30, 2016
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		$ 881	$ 1,649
Total gains or (losses) (realized or unrealized)
Included in earnings		46	(128)
Included in other comprehensive income		(28)	106
Purchases		61	191
Sales		(17)	(74)
Settlements		(246)	(633)
September 30, 2016		665	665
The amount of total gains for the period included in earnings attributable to the change in unrealized gains or losses relating to option contracts still held at September 30, 2016		(20)	95
Fuel derivatives
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		907	1,676
Total gains or (losses) (realized or unrealized)
Included in earnings		46	(128)
Included in other comprehensive income		(31)	104
Purchases	[1]	61	191
Sales	[1]	(4)	(61)
Settlements		(246)	(633)
September 30, 2016		681	681
The amount of total gains for the period included in earnings attributable to the change in unrealized gains or losses relating to option contracts still held at September 30, 2016		(20)	95
Other securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		26	27
Total gains or (losses) (realized or unrealized)
Included in earnings		0	0
Included in other comprehensive income		3	2
Purchases		0	0
Sales		(13)	(13)
Settlements		0	0
September 30, 2016		16	16
The amount of total gains for the period included in earnings attributable to the change in unrealized gains or losses relating to option contracts still held at September 30, 2016		$ 0	$ 0
[1] The purchase and sale of fuel derivatives are recorded gross based on the structure of the derivative instrument and whether a contract with multiple derivatives is purchased as a single instrument or separate instruments.

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This item represents the amount of the total realized and unrealized gains or losses for the period which are included in the statement of income (or changes in net assets); the fair value of which assets and liabilities was or is measured on a recurring basis using significant unobservable inputs (Level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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-Section 50
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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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-Publisher FASB
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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of gain (loss) recognized in other comprehensive income, arising from assets, liabilities and financial instruments classified in shareholders' equity measured at fair value on a recurring basis using unobservable inputs (level 3).

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Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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