FAIR VALUE MEASUREMENTS - FAIR VALUE OF ASSETS AND LIABILITIES (Details) - USD ($) $ in Millions | Sep. 30, 2022 | Dec. 31, 2021 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-Sale, Amortized Cost | $ 2,600 | |
Debt Securities, Available-for-Sale and Held-to-Maturity, Fair Value | 2,500 | |
Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, Fair Value Disclosure | 2,528 | $ 2,727 |
Derivative instruments, liabilities | 0 | 9 |
Debt Securities, Available-for-sale | 2,462 | 2,646 |
Level 1 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, Fair Value Disclosure | 537 | 337 |
Derivative instruments, liabilities | 0 | 0 |
Debt Securities, Available-for-sale | 537 | 337 |
Level 2 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, Fair Value Disclosure | 1,991 | 2,390 |
Derivative instruments, liabilities | 0 | 9 |
Debt Securities, Available-for-sale | 1,925 | 2,309 |
Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term debt | 708 | |
Fuel hedge contracts [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative instruments, assets | 51 | 81 |
Fuel hedge contracts [Member] | Level 1 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative instruments, assets | 0 | 0 |
Fuel hedge contracts [Member] | Level 2 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative instruments, assets | 51 | 81 |
Interest rate swaps agreements [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative instruments, assets | 15 | 0 |
Derivative instruments, liabilities | 0 | 9 |
Interest rate swaps agreements [Member] | Level 1 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative instruments, assets | 0 | 0 |
Derivative instruments, liabilities | 0 | 0 |
Interest rate swaps agreements [Member] | Level 2 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative instruments, assets | 15 | 0 |
Derivative instruments, liabilities | 0 | 9 |
U.S. government and agency securities [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 532 | 331 |
U.S. government and agency securities [Member] | Level 1 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 532 | 331 |
U.S. government and agency securities [Member] | Level 2 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 0 | 0 |
Equity Funds [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 5 | 6 |
Equity Funds [Member] | Level 1 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 5 | 6 |
Equity Funds [Member] | Level 2 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 0 | 0 |
Foreign government bonds [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 25 | 38 |
Foreign government bonds [Member] | Level 1 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 0 | 0 |
Foreign government bonds [Member] | Level 2 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 25 | 38 |
Asset-backed securities [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 260 | 311 |
Asset-backed securities [Member] | Level 1 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 0 | 0 |
Asset-backed securities [Member] | Level 2 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 260 | 311 |
Mortgage-backed securities [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 208 | 232 |
Mortgage-backed securities [Member] | Level 1 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 0 | 0 |
Mortgage-backed securities [Member] | Level 2 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 208 | 232 |
Corporate notes and bonds [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 1,384 | 1,663 |
Corporate notes and bonds [Member] | Level 1 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 0 | 0 |
Corporate notes and bonds [Member] | Level 2 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 1,384 | 1,663 |
Municipal securities [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 48 | 65 |
Municipal securities [Member] | Level 1 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | 0 | 0 |
Municipal securities [Member] | Level 2 [Member] | Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Debt Securities, Available-for-sale | $ 48 | $ 65 |