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FINANCING ACTIVITIES - Narrative (Details) |  |  | 3 Months Ended | 12 Months Ended |  |  |  |  |  |  |  |  |  |
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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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