Debt - Details of Pass Through Trusts (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) aircraft	Dec. 31, 2018 USD ($)		Dec. 31, 2017 USD ($)	[1]
Debt Instrument [Line Items]
Total debt recorded	$ 14,733,000,000	$ 13,636,000,000
Proceeds received from issuance of debt	$ 1,847,000,000	$ 1,594,000,000	[1]	$ 2,537,000,000
Boeing 737 MAX
Debt Instrument [Line Items]
Number of aircraft expected to take delivery of | aircraft	3
Pass-Through Certificates
Debt Instrument [Line Items]
Principal	$ 2,234,000,000
Total debt recorded	1,813,000,000
Proceeds received from issuance of debt	1,813,000,000
Amounts returned to holders of pass through certificates	93,000,000
Remaining proceeds from issuance of debt to be received in future periods	328,000,000
Class AA Pass Through Certificates Issued September 2019 | Pass-Through Certificates
Debt Instrument [Line Items]
Principal	$ 702,000,000
Stated interest rate	2.70%
Total debt recorded	$ 513,000,000
Proceeds received from issuance of debt	513,000,000
Amounts returned to holders of pass through certificates	0
Remaining proceeds from issuance of debt to be received in future periods	189,000,000
Class A Pass Through Certificates Issued September 2019 | Pass-Through Certificates
Debt Instrument [Line Items]
Principal	$ 287,000,000
Stated interest rate	2.90%
Total debt recorded	$ 210,000,000
Proceeds received from issuance of debt	210,000,000
Amounts returned to holders of pass through certificates	0
Remaining proceeds from issuance of debt to be received in future periods	77,000,000
Class B Pass Through Certificates Issued September 2019 | Pass-Through Certificates
Debt Instrument [Line Items]
Principal	$ 232,000,000
Stated interest rate	3.50%
Total debt recorded	$ 170,000,000
Proceeds received from issuance of debt	170,000,000
Amounts returned to holders of pass through certificates	0
Remaining proceeds from issuance of debt to be received in future periods	62,000,000
Class AA Pass Through Certificates Issued February 2019 | Pass-Through Certificates
Debt Instrument [Line Items]
Principal	$ 717,000,000
Stated interest rate	4.15%
Total debt recorded	$ 651,000,000
Proceeds received from issuance of debt	651,000,000
Amounts returned to holders of pass through certificates	66,000,000
Remaining proceeds from issuance of debt to be received in future periods	0
Class A Pass Through Certificates Issued February 2019 | Pass-Through Certificates
Debt Instrument [Line Items]
Principal	$ 296,000,000
Stated interest rate	4.55%
Total debt recorded	$ 269,000,000
Proceeds received from issuance of debt	269,000,000
Amounts returned to holders of pass through certificates	27,000,000
Remaining proceeds from issuance of debt to be received in future periods	$ 0

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2016-02, Leases (Topic 842). See Note 1 to the financial statements contained in Part II, Item 8 of this report for additional information.