FAIR VALUE MEASUREMENTS - Fair Value Of Financial Instruments On A Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	$ 1,274
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	1,274	$ 1,510
Total Assets	1,283	1,529
Fair Value, Measurements, Recurring | Interest rate swap agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments	9	8
Fair Value, Measurements, Recurring | Fuel hedge contracts - call options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments		11
Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	292	387
Fair Value, Measurements, Recurring | Equity mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	7	5
Fair Value, Measurements, Recurring | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	134	192
Fair Value, Measurements, Recurring | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	112	115
Fair Value, Measurements, Recurring | Corporate notes and bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	698	763
Fair Value, Measurements, Recurring | Municipal securities and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	31	38
Fair Value, Measurements, Recurring | Debt Security, Government, Non-US
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities		10
Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	299	392
Total Assets	299	392
Level 1 | Fair Value, Measurements, Recurring | Interest rate swap agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments	0	0
Level 1 | Fair Value, Measurements, Recurring | Fuel hedge contracts - call options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments		0
Level 1 | Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	292	387
Level 1 | Fair Value, Measurements, Recurring | Equity mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	7	5
Level 1 | Fair Value, Measurements, Recurring | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	0	0
Level 1 | Fair Value, Measurements, Recurring | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	0	0
Level 1 | Fair Value, Measurements, Recurring | Corporate notes and bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	0	0
Level 1 | Fair Value, Measurements, Recurring | Municipal securities and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	0	0
Level 1 | Fair Value, Measurements, Recurring | Debt Security, Government, Non-US
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities		0
Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	966	1,118
Total Assets	975	1,137
Level 2 | Fair Value, Measurements, Recurring | Interest rate swap agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments	9	8
Level 2 | Fair Value, Measurements, Recurring | Fuel hedge contracts - call options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments		11
Level 2 | Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	0	0
Level 2 | Fair Value, Measurements, Recurring | Equity mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	0	0
Level 2 | Fair Value, Measurements, Recurring | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	127	192
Level 2 | Fair Value, Measurements, Recurring | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	112	115
Level 2 | Fair Value, Measurements, Recurring | Corporate notes and bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	696	763
Level 2 | Fair Value, Measurements, Recurring | Municipal securities and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	31	38
Level 2 | Fair Value, Measurements, Recurring | Debt Security, Government, Non-US
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities		10
Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	9	0
Total Assets	9	0
Level 3 | Fair Value, Measurements, Recurring | Interest rate swap agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments	0	0
Level 3 | Fair Value, Measurements, Recurring | Fuel hedge contracts - call options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments		0
Level 3 | Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	0	0
Level 3 | Fair Value, Measurements, Recurring | Equity mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	0	0
Level 3 | Fair Value, Measurements, Recurring | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	7	0
Level 3 | Fair Value, Measurements, Recurring | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	0	0
Level 3 | Fair Value, Measurements, Recurring | Corporate notes and bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	2	0
Level 3 | Fair Value, Measurements, Recurring | Municipal securities and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities	$ 0	0
Level 3 | Fair Value, Measurements, Recurring | Debt Security, Government, Non-US
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Marketable securities		$ 0