Number of new aircraft held as security.

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The carrying amount, as of the date of the latest financial statement presented, of flight equipment which are owned but transferred to serve as collateral for the payment of the related debt obligation, primarily a secured borrowing or repurchase agreement, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

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The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

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Face (par) amount of debt instrument at time of issuance.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of lessee's undiscounted obligation for lease payments for finance lease, due after fifth fiscal year following latest fiscal year.

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Amount of cash paid for interest, including, but not limited to, capitalized interest and payment to settle zero-coupon bond attributable to accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount; classified as operating and investing activities.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of long-term debt and lease obligation, classified as noncurrent.

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Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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Long-term Debt, Short-term Borrowings, and Capital Lease Obligations (Details Textual)	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) aircraft	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Long-term Debt	$ 2,245,000,000	$ 1,563,000,000
Capital Leases, Future Minimum Payments Due [Abstract]
Thereafter	0
Long-term debt and capital lease obligations	1,990,000,000	1,361,000,000
Value of aircraft, engines and other equipment and facilities which were pledged as security under various loan agreements	4,300,000,000
Cash payments for interest related to debt and capital lease obligations, net of capitalized interest	62,000,000	59,000,000	$ 60,000,000
Morgan Stanley [Member]
Capital Leases, Future Minimum Payments Due [Abstract]
Line of Credit Facility, Current Borrowing Capacity	$ 200,000,000
Morgan Stanley [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Capital Leases, Future Minimum Payments Due [Abstract]
Debt Instrument, Description of Variable Rate Basis	LIBOR, plus a margin
Line of Credit [Member] \| Morgan Stanley [Member] \| Revolving Credit Facility and Letter of Credit Facility [Member]
Capital Leases, Future Minimum Payments Due [Abstract]
Long-term Line of Credit	$ 0	0
Line of Credit [Member] \| Citibank [Member] \| Revolving Credit Facility and Letter of Credit Facility [Member]
Capital Leases, Future Minimum Payments Due [Abstract]
Long-term Line of Credit	0	0
Line of Credit Facility, Current Borrowing Capacity	$ 550,000,000
Line of Credit [Member] \| Citibank [Member] \| Revolving Credit Facility and Letter of Credit Facility [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Capital Leases, Future Minimum Payments Due [Abstract]
Debt Instrument, Description of Variable Rate Basis	LIBOR, plus a margin
Aircraft [Domain]
Capital Leases, Future Minimum Payments Due [Abstract]
Thereafter	$ 0
Floating rate equipment notes due through 2028 [Member]
Debt Instrument [Line Items]
Secured Debt	$ 201,000,000	247,000,000
Face value of convertible debt issued		$ 120,000,000
Floating rate equipment notes due through 2028 [Member] \| Secured Debt [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Capital Leases, Future Minimum Payments Due [Abstract]
Debt Instrument, Description of Variable Rate Basis	LIBOR, plus a margin
Floating rate equipment notes due through 2028 [Member] \| A-321 [Member] \| Secured Debt [Member]
Capital Leases, Future Minimum Payments Due [Abstract]
Number of New Aircraft Held As Security \| aircraft		1
Floating rate equipment notes due through 2028 [Member] \| A-320 [Member] \| Secured Debt [Member]
Capital Leases, Future Minimum Payments Due [Abstract]
Number of New Aircraft Held As Security \| aircraft		6