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FINANCING ACTIVITIES - Narrative (Details)			3 Months Ended	12 Months Ended
	Jan. 09, 2023	Feb. 28, 1997 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Jan. 01, 2022 USD ($)	Dec. 31, 2021 USD ($) $ / shares	Dec. 31, 2020 USD ($)	Jul. 31, 2020 USD ($)	Jun. 08, 2020 USD ($)	May 04, 2020 USD ($)	May 01, 2020 USD ($) $ / shares	Feb. 29, 2020 USD ($)	Nov. 30, 2017 USD ($)	Nov. 30, 2016 USD ($)
Debt Instrument [Line Items]
Initial conversion price (in USD per share) | $ / shares							$ 38.48
Minimum level of liquidity required			$ 1,500,000,000	$ 1,500,000,000
Outstanding letters of credit			110,000,000	110,000,000
Net book value of assets pledged as collateral for the Company's secured borrowings, primarily aircraft and engines					$ 2,000,000,000
Long-term debt			8,012,000,000	8,012,000,000
Stockholders' equity attributable to parent			10,515,000,000	10,515,000,000	10,687,000,000		$ 10,414,000,000	$ 8,876,000,000
Capital in excess of par value
Debt Instrument [Line Items]
Stockholders' equity attributable to parent			4,153,000,000	4,153,000,000	4,037,000,000		4,224,000,000	4,191,000,000
Cumulative Effect, Period of Adoption, Adjustment
Debt Instrument [Line Items]
Stockholders' equity attributable to parent							(245,000,000)	0
Cumulative Effect, Period of Adoption, Adjustment | Capital in excess of par value
Debt Instrument [Line Items]
Stockholders' equity attributable to parent							$ (300,000,000)
Accounting Standards Update 2020-06 | Cumulative Effect, Period of Adoption, Adjustment | Capital in excess of par value
Debt Instrument [Line Items]
Stockholders' equity attributable to parent						$ (300,000,000)
Aircraft
Debt Instrument [Line Items]
Net book value of assets pledged as collateral for the Company's secured borrowings, primarily aircraft and engines					296,000,000
Revolving Credit Facility
Debt Instrument [Line Items]
Credit outstanding			$ 0	$ 0	0
Convertible Notes
Debt Instrument [Line Items]
Interest rate stated in the debt agreement (as a percent)						1.25%
Term (in years)				5 years
Effective interest rate (as a percent)			1.90%	1.90%
Convertible Notes | Accounting Standards Update 2020-06
Debt Instrument [Line Items]
Long-term debt						$ 300,000,000
Convertible Notes | Accounting Standards Update 2020-06 | Cumulative Effect, Period of Adoption, Adjustment | Capital in excess of par value
Debt Instrument [Line Items]
Stockholders' equity attributable to parent						$ 300,000,000
Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 1,000,000,000	$ 1,000,000,000
Total 5.125 Notes due 2027 | Unsecured Debt
Debt Instrument [Line Items]
Long term debt								$ 2,000,000,000
5.125 Unsecured Notes due 2027
Debt Instrument [Line Items]
Face amount of debt										$ 1,300,000,000
5.125% Notes due 2027 | Unsecured Debt
Debt Instrument [Line Items]
Long term debt			1,727,000,000	1,727,000,000	$ 1,727,000,000				$ 700,000,000
Interest rate stated in the debt agreement (as a percent)					5.125%			5.125%
Repayments of debt					$ 285,000,000
Early prepayments made on debt					$ 272,000,000
5.25% Notes due 2025
Debt Instrument [Line Items]
Face amount of debt								$ 1,550,000,000			$ 1,250,000,000
5.25% Notes due 2025 | Unsecured Debt
Debt Instrument [Line Items]
Long term debt									$ 300,000,000
Interest rate stated in the debt agreement (as a percent)					5.25%			5.25%
Repayments of debt					$ 258,000,000
Early prepayments made on debt					248,000,000
5.25% Notes due 2025 | Convertible Notes
Debt Instrument [Line Items]
Long term debt			$ 1,302,000,000	1,302,000,000	1,302,000,000
1.25% Convertible Notes due 2025
Debt Instrument [Line Items]
Conversion ratio (in shares)	0.0267188		0.0259909
Initial conversion price (in USD per share) | $ / shares												$ 38.48
If-converted value exceeded principal amount				368,000,000
1.25% Convertible Notes due 2025 | Unsecured Debt
Debt Instrument [Line Items]
Long term debt			$ 1,611,000,000	$ 1,611,000,000	$ 1,611,000,000
1.25% Convertible Notes due 2025 | Convertible Notes
Debt Instrument [Line Items]
Face amount of debt												$ 2,300,000,000
Interest rate stated in the debt agreement (as a percent)					1.25%							1.25%
Repayments of debt					$ 649,000,000
Amended 364-Day Term Loan Credit Facility
Debt Instrument [Line Items]
Interest rate stated in the debt agreement (as a percent)			1.00%	1.00%
Amended 364-Day Term Loan Credit Facility | Minimum
Debt Instrument [Line Items]
Interest rate stated in the debt agreement (as a percent)			1.00%	1.00%
Amended 364-Day Term Loan Credit Facility | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Interest rate stated in the debt agreement (as a percent)			0.10%	0.10%
Amended 364-Day Term Loan Credit Facility | New York Fed Bank Rate
Debt Instrument [Line Items]
Interest rate stated in the debt agreement (as a percent)			0.50%	0.50%
Amended 364-Day Term Loan Credit Facility | Base Rate | Minimum
Debt Instrument [Line Items]
Interest rate stated in the debt agreement (as a percent)			1.00%	1.00%
2.625% Notes due 2030
Debt Instrument [Line Items]
Face amount of debt													$ 500,000,000
2.625% Notes due 2030 | Unsecured Debt
Debt Instrument [Line Items]
Long term debt			$ 500,000,000	$ 500,000,000	500,000,000
Interest rate stated in the debt agreement (as a percent)			2.625%	2.625%
Unsecured Senior Notes Due 2027 - 3.45%
Debt Instrument [Line Items]
Face amount of debt														$ 300,000,000
Interest rate stated in the debt agreement (as a percent)														3.45%
Unsecured Senior Notes Due 2027 - 3.45% | Treasury Rate
Debt Instrument [Line Items]
Spread on variable rate (as a percent)		0.20%
3.00% Notes due 2026
Debt Instrument [Line Items]
Face amount of debt															$ 300,000,000
Interest rate stated in the debt agreement (as a percent)															3.00%
7.375% Debentures due 2027
Debt Instrument [Line Items]
Face amount of debt		$ 100,000,000
Interest rate stated in the debt agreement (as a percent)		7.375%
7.375% Debentures due 2027 | Unsecured Debt
Debt Instrument [Line Items]
Long term debt			$ 111,000,000	$ 111,000,000	114,000,000
Interest rate stated in the debt agreement (as a percent)			7.375%	7.375%
Convertible Debt, Liability Component | Convertible Notes
Debt Instrument [Line Items]
Long term debt			$ 1,600,000,000	$ 1,600,000,000	$ 1,600,000,000

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