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RECENTLY ADOPTED ACCOUNTING PRONOUNCEMENTS (Details) - USD ($) $ in Millions | 3 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Mar. 31, 2018 | Dec. 31, 2017 | Mar. 31, 2017 | Jan. 01, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Cash and cash equivalents |  |  | $ 177 | $ 194 | $ 183 |
Cash, cash equivalents, and restricted cash | $ 197 | $ 328 | 183 | 197 | 183 |
Current Assets |  |  |  |  |  |
Prepaid expenses and other current assets |  |  | 174 | 133 |  |
Current Liabilities |  |  |  |  |  |
Air traffic liability |  |  | 1,122 | 806 |  |
Other accrued liabilities |  |  | 433 | 400 |  |
Deferred revenue, current |  |  | 649 | 635 |  |
Other Liabilities and Credits |  |  |  |  |  |
Deferred income taxes |  |  | 372 | 370 |  |
Deferred revenue, noncurrent |  |  | 1,102 | 1,090 |  |
Other liabilities |  |  | 423 | 425 |  |
Shareholders' Equity |  |  |  |  |  |
Retained earnings |  |  | $ 4,219 | 4,193 |  |
Operating Revenues |  |  |  |  |  |
Passenger revenues | 1,685 | 1,602 |  |  |  |
Mileage plan other revenue | 107 | 100 |  |  |  |
Cargo and other | 40 | 38 |  |  |  |
Total Operating Revenues | 1,832 | 1,740 |  |  |  |
Operating Expenses |  |  |  |  |  |
Wages and benefits | 536 | 450 |  |  |  |
Selling expenses | 78 | 83 |  |  |  |
Special items—merger-related costs | 6 | 39 |  |  |  |
All other operating expenses |  | 1,011 |  |  |  |
Total Operating Expenses | 1,803 | 1,583 |  |  |  |
Operating Income | 29 | 157 |  |  |  |
Nonoperating Income (Expense) |  |  |  |  |  |
Other—net | (12) | (1) |  |  |  |
All other nonoperating income (expense) |  | (14) |  |  |  |
Nonoperating Income (Expense) Total | (23) | (15) |  |  |  |
Income Before Income Tax | 6 | 142 |  |  |  |
Income tax expense | 2 | 49 |  |  |  |
Net Income (loss) | 4 | 93 |  |  |  |
Adjustments to reconcile net income to net cash provided by operating activities: |  |  |  |  |  |
Depreciation and amortization | 94 | 90 |  |  |  |
Stock-based compensation and other | 8 | 13 |  |  |  |
Changes in deferred tax provision | 2 | 44 |  |  |  |
Increase in air traffic liability | 316 | 364 |  |  |  |
Increase in deferred revenue | 26 | 31 |  |  |  |
Other—net | (144) | (165) |  |  |  |
Net cash provided by operating activities | 306 | 470 |  |  |  |
Net cash used in investing activities | (164) | (488) |  |  |  |
Net cash used in financing activities | (156) | (127) |  |  |  |
Net increase (decrease) in cash, cash equivalents, and restricted cash | (14) | (145) |  |  |  |
Cash, cash equivalents, and restricted cash at beginning of year | 197 | 328 |  |  |  |
Cash, cash equivalents, and restricted cash at end of the period | $ 183 | 183 |  |  |  |
As Reported [Member] |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Cash, cash equivalents, and restricted cash |  | 328 |  |  | 183 |
Current Assets |  |  |  |  |  |
Prepaid expenses and other current assets |  |  |  | 127 |  |
Current Liabilities |  |  |  |  |  |
Air traffic liability |  |  |  | 937 |  |
Deferred revenue, current |  |  |  | 518 |  |
Other Liabilities and Credits |  |  |  |  |  |
Deferred income taxes |  |  |  | 454 |  |
Deferred revenue, noncurrent |  |  |  | 699 |  |
Other liabilities |  |  |  | 451 |  |
Shareholders' Equity |  |  |  |  |  |
Retained earnings |  |  |  | 4,454 |  |
Operating Revenues |  |  |  |  |  |
Passenger revenues |  | 1,484 |  |  |  |
Mileage plan other revenue |  | 119 |  |  |  |
Cargo and other |  | 146 |  |  |  |
Total Operating Revenues |  | 1,749 |  |  |  |
Operating Expenses |  |  |  |  |  |
Wages and benefits |  | 448 |  |  |  |
Selling expenses |  | 81 |  |  |  |
Special items—merger-related costs |  | 40 |  |  |  |
All other operating expenses |  | 1,011 |  |  |  |
Total Operating Expenses |  | 1,580 |  |  |  |
Operating Income |  | 169 |  |  |  |
Nonoperating Income (Expense) |  |  |  |  |  |
Other—net |  | (3) |  |  |  |
All other nonoperating income (expense) |  | (14) |  |  |  |
Nonoperating Income (Expense) Total |  | (17) |  |  |  |
Income Before Income Tax |  | 152 |  |  |  |
Income tax expense |  | 53 |  |  |  |
Net Income (loss) |  | 99 |  |  |  |
Adjustments to reconcile net income to net cash provided by operating activities: |  |  |  |  |  |
Depreciation and amortization |  | 90 |  |  |  |
Stock-based compensation and other |  | 13 |  |  |  |
Changes in deferred tax provision |  | 48 |  |  |  |
Increase in air traffic liability |  | 369 |  |  |  |
Increase in deferred revenue |  | 1 |  |  |  |
Other—net |  | (150) |  |  |  |
Net cash provided by operating activities |  | 470 |  |  |  |
Net cash used in investing activities |  | (488) |  |  |  |
Net cash used in financing activities |  | (127) |  |  |  |
Net increase (decrease) in cash, cash equivalents, and restricted cash |  | (145) |  |  |  |
Cash, cash equivalents, and restricted cash at beginning of year |  | 328 |  |  |  |
Cash, cash equivalents, and restricted cash at end of the period |  | 183 |  |  |  |
Accounting Standards Update 2014-09 [Member] |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Cumulative effect of new accounting pronouncements |  |  |  |  |  | $ 171
Accounting Standards Update 2014-09 [Member] | Adjustments [Member] |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Cash, cash equivalents, and restricted cash |  | 0 |  |  | $ 0 |
Current Assets |  |  |  |  |  |
Prepaid expenses and other current assets |  |  |  | 6 |  |
Current Liabilities |  |  |  |  |  |
Air traffic liability |  |  |  | (131) |  |
Deferred revenue, current |  |  |  | 117 |  |
Other Liabilities and Credits |  |  |  |  |  |
Deferred income taxes |  |  |  | (84) |  |
Deferred revenue, noncurrent |  |  |  | 391 |  |
Other liabilities |  |  |  | (26) |  |
Shareholders' Equity |  |  |  |  |  |
Retained earnings |  |  |  | $ (261) |  |
Operating Revenues |  |  |  |  |  |
Passenger revenues |  | 118 |  |  |  |
Mileage plan other revenue |  | (19) |  |  |  |
Cargo and other |  | (108) |  |  |  |
Total Operating Revenues |  | (9) |  |  |  |
Operating Expenses |  |  |  |  |  |
Wages and benefits |  | 0 |  |  |  |
Selling expenses |  | 2 |  |  |  |
Special items—merger-related costs |  | (1) |  |  |  |
All other operating expenses |  | 0 |  |  |  |
Total Operating Expenses |  | 1 |  |  |  |
Operating Income |  | (10) |  |  |  |
Nonoperating Income (Expense) |  |  |  |  |  |
Other—net |  | 0 |  |  |  |
All other nonoperating income (expense) |  | 0 |  |  |  |
Nonoperating Income (Expense) Total |  | 0 |  |  |  |
Income Before Income Tax |  | (10) |  |  |  |
Income tax expense |  | (4) |  |  |  |
Net Income (loss) |  | (6) |  |  |  |
Adjustments to reconcile net income to net cash provided by operating activities: |  |  |  |  |  |
Depreciation and amortization |  | 0 |  |  |  |
Stock-based compensation and other |  | 0 |  |  |  |
Changes in deferred tax provision |  | (4) |  |  |  |
Increase in air traffic liability |  | (5) |  |  |  |
Increase in deferred revenue |  | 30 |  |  |  |
Other—net |  | (15) |  |  |  |
Net cash provided by operating activities |  | 0 |  |  |  |
Net cash used in investing activities |  | 0 |  |  |  |
Net cash used in financing activities |  | 0 |  |  |  |
Net increase (decrease) in cash, cash equivalents, and restricted cash |  | 0 |  |  |  |
Cash, cash equivalents, and restricted cash at beginning of year |  | 0 |  |  |  |
Cash, cash equivalents, and restricted cash at end of the period |  | 0 |  |  |  |
Accounting Standards Update 2017-07 [Member] | Adjustments [Member] |  |  |  |  |  |
Operating Revenues |  |  |  |  |  |
Passenger revenues |  | 0 |  |  |  |
Mileage plan other revenue |  | 0 |  |  |  |
Cargo and other |  | 0 |  |  |  |
Total Operating Revenues |  | 0 |  |  |  |
Operating Expenses |  |  |  |  |  |
Wages and benefits |  | 2 |  |  |  |
Selling expenses |  | 0 |  |  |  |
Special items—merger-related costs |  | 0 |  |  |  |
All other operating expenses |  | 0 |  |  |  |
Total Operating Expenses |  | 2 |  |  |  |
Operating Income |  | (2) |  |  |  |
Nonoperating Income (Expense) |  |  |  |  |  |
Other—net |  | 2 |  |  |  |
All other nonoperating income (expense) |  | 0 |  |  |  |
Nonoperating Income (Expense) Total |  | 2 |  |  |  |
Income Before Income Tax |  | 0 |  |  |  |
Income tax expense |  | 0 |  |  |  |
Net Income (loss) |  | $ 0 |  |  |  |

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- Definition Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
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