FINANCING ACTIVITIES - Narrative (Details)				3 Months Ended	12 Months Ended
	Dec. 31, 2024 USD ($)	May 01, 2020 USD ($) $ / shares	Feb. 28, 1997 USD ($)	Jun. 30, 2024 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Jan. 01, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jul. 31, 2020 USD ($)	Jun. 08, 2020 USD ($)	May 04, 2020 USD ($)	Feb. 29, 2020 USD ($)	Nov. 30, 2017 USD ($)	Nov. 30, 2016 USD ($)
Debt Instrument [Line Items]
Stockholders' equity attributable to parent	$ 10,350,000,000				$ 10,350,000,000	$ 10,515,000,000	$ 10,687,000,000		$ 10,414,000,000
Long-term debt	6,697,000,000				6,697,000,000
Payments for repurchased common stock warrants				$ 6,000,000	6,000,000	0	0
Minimum level of liquidity required	1,500,000,000				1,500,000,000
Outstanding letters of credit	377,000,000				377,000,000
Net book value of assets pledged as collateral for the Company's secured borrowings, primarily aircraft and engines	0				0
Revolving Credit Facility
Debt Instrument [Line Items]
Credit outstanding	0				0	0
Capital in excess of par value
Debt Instrument [Line Items]
Stockholders' equity attributable to parent	$ 4,199,000,000				$ 4,199,000,000	4,153,000,000	4,037,000,000		4,224,000,000
Cumulative Effect, Period of Adoption, Adjustment
Debt Instrument [Line Items]
Stockholders' equity attributable to parent									(245,000,000)
Cumulative Effect, Period of Adoption, Adjustment | Capital in excess of par value
Debt Instrument [Line Items]
Stockholders' equity attributable to parent									$ (300,000,000)
Convertible Notes
Debt Instrument [Line Items]
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 | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2020-06 | 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 | 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%					5.125%
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	$ 0				$ 0	1,302,000,000					$ 300,000,000
Interest rate stated in the debt agreement (as a percent)	5.25%				5.25%					5.25%
Early prepayments made on debt							$ 248,000,000
2.625% Notes
Debt Instrument [Line Items]
Face amount of debt														$ 500,000,000
Interest rate stated in the debt agreement (as a percent)														2.625%
2.625% Notes | 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
Debt Instrument [Line Items]
Face amount of debt																$ 300,000,000
Interest rate stated in the debt agreement (as a percent)																3.00%
3.00% Notes | Unsecured Debt
Debt Instrument [Line Items]
Long term debt	$ 300,000,000				$ 300,000,000	300,000,000
Interest rate stated in the debt agreement (as a percent)	3.00%				3.00%
7.375% Debentures
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 | Unsecured Debt
Debt Instrument [Line Items]
Long term debt	$ 107,000,000				$ 107,000,000	111,000,000
Interest rate stated in the debt agreement (as a percent)	7.375%				7.375%
1.25% Convertible Notes
Debt Instrument [Line Items]
Conversion ratio (in shares)	0.0273384	0.0259909
Initial conversion price (in USD per share) | $ / shares		$ 38.48
If-converted value exceeded principal amount					$ 130,000,000
1.25% Convertible Notes | Convertible Notes
Debt Instrument [Line Items]
Long term debt	$ 1,611,000,000				$ 1,611,000,000	$ 1,611,000,000
Face amount of debt		$ 2,300,000,000
Interest rate stated in the debt agreement (as a percent)	1.25%	1.25%			1.25%
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)
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%