RECENTLY ADOPTED ACCOUNTING PRONOUNCEMENTS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jan. 01, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents					$ 174	$ 194	$ 144
Cash, cash equivalents, and restricted cash	$ 184	$ 144	$ 197	$ 328	184	197	144
Current Assets
Prepaid expenses and other current assets					180	133
Current Liabilities
Air traffic liability					950	806
Other accrued liabilities					452	400
Deferred revenue, current					693	635
Other Liabilities and Credits
Deferred income taxes					494	370
Deferred revenue, noncurrent					1,138	1,090
Other liabilities					428	425
Shareholders' Equity
Retained earnings					$ 4,550	$ 4,193
Operating Revenues
Total Operating Revenues	2,212	2,110	6,200	5,952
Operating Expenses
Wages and benefits	549	477	1,629	1,397
Selling expenses	79	92	245	277
Special items—merger-related costs	22	23	67	86
All other operating expenses		1,091		3,121
Total Operating Expenses	1,915	1,683	5,603	4,881
Operating Income	297	427	597	1,071
Nonoperating Income (Expense)
Other—net	(7)	2	(20)	1
Nonoperating Income (Expense), Other		(12)		(39)
Nonoperating Income (Expense) Total	(13)	(10)	(48)	(38)
Income Before Income Tax	284	417	549	1,033
Income tax expense	67	158	135	388
Net Income (loss)	217	259	414	645
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	99	95	290	275
Stock-based compensation and other			34	43
Changes in deferred tax provision			122	208
Increase in air traffic liability			144	223
Increase in deferred revenue			106	130
Other—net			(124)	(167)
Net cash provided by operating activities			986	1,357
Net cash used in investing activities			(333)	(1,142)
Net cash used in financing activities			(666)	(399)
Net increase (decrease) in cash, cash equivalents, and restricted cash			(13)	(184)
Cash, cash equivalents, and restricted cash at beginning of year			197	328
Cash, cash equivalents, and restricted cash at end of the period	184	144	184	144
As Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash, cash equivalents, and restricted cash		144		328			144
Operating Revenues
Mileage plan other revenue		122		369
Total Operating Revenues		2,120		5,971
Operating Expenses
Wages and benefits		475		1,392
Selling expenses		91		269
Special items—merger-related costs		24		88
All other operating expenses		1,091		3,121
Total Operating Expenses		1,681		4,870
Operating Income		439		1,101
Nonoperating Income (Expense)
Other—net		0		(4)
Nonoperating Income (Expense), Other		(12)		(39)
Nonoperating Income (Expense) Total		(12)		(43)
Income Before Income Tax		427		1,058
Income tax expense		161		397
Net Income (loss)		266		661
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization				275
Stock-based compensation and other				43
Changes in deferred tax provision				217
Increase in air traffic liability				254
Increase in deferred revenue				46
Other—net				(139)
Net cash provided by operating activities				1,357
Net cash used in investing activities				(1,142)
Net cash used in financing activities				(399)
Net increase (decrease) in cash, cash equivalents, and restricted cash				(184)
Cash, cash equivalents, and restricted cash at beginning of year				328
Cash, cash equivalents, and restricted cash at end of the period		144		144
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			$ 0
Operating Revenues
Mileage plan other revenue		(17)		(55)
Total Operating Revenues		(10)		(19)
Operating Expenses
Wages and benefits		0		0
Selling expenses		1		8
Special items—merger-related costs		(1)		(2)
All other operating expenses		0		0
Total Operating Expenses		0		6
Operating Income		(10)		(25)
Nonoperating Income (Expense)
Other—net		0		0
Nonoperating Income (Expense), Other		0		0
Nonoperating Income (Expense) Total		0		0
Income Before Income Tax		(10)		(25)
Income tax expense		(3)		(9)
Net Income (loss)		(7)		(16)
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				(9)
Increase in air traffic liability				(31)
Increase in deferred revenue				84
Other—net				(28)
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		0
Accounting Standards Update 2017-07 [Member] | Adjustments [Member]
Operating Revenues
Mileage plan other revenue		0		0
Total Operating Revenues		0		0
Operating Expenses
Wages and benefits		2		5
Selling expenses		0		0
Special items—merger-related costs		0		0
All other operating expenses		0		0
Total Operating Expenses		2		5
Operating Income		(2)		(5)
Nonoperating Income (Expense)
Other—net		2		5
Nonoperating Income (Expense), Other		0		0
Nonoperating Income (Expense) Total		2		5
Income Before Income Tax		0		0
Income tax expense		0		0
Net Income (loss)		0		0
Cargo and Freight [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	55	47	146	133
Cargo and Freight [Member] | As Reported [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes		174		487
Cargo and Freight [Member] | Accounting Standards Update 2014-09 [Member] | Adjustments [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes		(127)		(354)
Cargo and Freight [Member] | Accounting Standards Update 2017-07 [Member] | Adjustments [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes		0		0
Passenger [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes	2,043	1,958	5,725	5,505
Passenger [Member] | As Reported [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes		1,824		5,115
Passenger [Member] | Accounting Standards Update 2014-09 [Member] | Adjustments [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes		134		390
Passenger [Member] | Accounting Standards Update 2017-07 [Member] | Adjustments [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes		0		0
Cargo and Other Revenue [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	55	47	146	133
Cargo and Other Revenue [Member] | Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 55	$ 47	$ 146	$ 133