Prospective change in estimate of updating the company's estimated selling price of an airline mile.

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Number of Call Options To Purchase Regional Jet Aircraft

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Number of elements identified in the agreement.

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- Definition

Refundable Tickets Expiration Period

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- Definition

Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 720

-SubTopic 35

-Section 50

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- Definition

Amount before accumulated amortization of capitalized costs for computer software, including but not limited to, acquired and internally developed computer software.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 985

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (a)

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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

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Per share amount effect of a restatement of results of operations on basic earnings per share.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 55

-Paragraph 15

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Per share amount effect of a restatement of results of operations on diluted earnings per share.

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Stated as a percentage, the estimated or actual value of the asset at the end of its useful life or when it is no longer serviceable (cannot be used for its original purpose) divided by its [historical] capitalized cost.

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Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Option	Dec. 31, 2013	Dec. 31, 2012
Significant Accounting Policies [Line Items]
Carrying value of computer software	$ 281	$ 290
Number of call options to purchase regional jet aircraft	281
Advertising expense	179us-gaap_AdvertisingExpense	178us-gaap_AdvertisingExpense	154us-gaap_AdvertisingExpense
Co-Brand Agreement
Significant Accounting Policies [Line Items]
Number of elements identified in agreement	5
Frequent Flyer
Significant Accounting Policies [Line Items]
Estimated impact of change on consolidated revenue	95
Impact of change resulted in increase in consolidated revenue basic share	$ 0.26
Impact of change resulted in increase in consolidated revenue diluted share	$ 0.24
Minimum
Significant Accounting Policies [Line Items]
Refundable tickets expiration period	1 year
Residual value	10.00%
Maximum
Significant Accounting Policies [Line Items]
Residual value	11.00%
Computer software
Significant Accounting Policies [Line Items]
Depreciation expense related to computer software	$ 81	$ 72	$ 81
Aircraft and related rotable parts \| Minimum
Significant Accounting Policies [Line Items]
Residual value	10.00%
Aircraft and related rotable parts \| Maximum
Significant Accounting Policies [Line Items]
Residual value	11.00%