RECENTLY ADOPTED ACCOUNTING PRONOUNCEMENTS (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Jan. 01, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents					$ 102	$ 194	$ 198
Cash, cash equivalents, and restricted cash	$ 108	$ 198	$ 197	$ 328	108	197	198
Current Assets
Prepaid expenses and other current assets					180	133
Current Liabilities
Air traffic liability					1,112	806
Other accrued liabilities					483	400
Deferred revenue, current					667	635
Other Liabilities and Credits
Deferred income taxes					437	370
Deferred revenue, noncurrent					1,110	1,090
Other liabilities					417	425
Shareholders' Equity
Retained earnings					$ 4,373	$ 4,193
Operating Revenues
Total Operating Revenues	2,156	2,102	3,988	3,842
Operating Expenses
Wages and benefits	544	470	1,080	920
Selling expenses	88	102	166	185
Special items—merger-related costs	39	24	45	63
All other operating expenses		1,019		2,030
Total Operating Expenses	1,885	1,615	3,688	3,198
Operating Income	271	487	300	644
Nonoperating Income (Expense)
Other—net	(1)	0	(13)	(1)
Nonoperating Income (Expense), Other		(13)		(27)
Nonoperating Income (Expense) Total	(12)	(13)	(35)	(28)
Income Before Income Tax	259	474	265	616
Income tax expense	66	181	68	230
Net Income (loss)	193	293	197	386
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	97	90	191	180
Stock-based compensation and other			17	25
Changes in deferred tax provision			67	127
Increase in air traffic liability			306	384
Increase in deferred revenue			52	69
Other—net			(104)	(87)
Net cash provided by operating activities			726	1,084
Net cash used in investing activities			(468)	(971)
Net cash used in financing activities			(347)	(243)
Net increase (decrease) in cash, cash equivalents, and restricted cash			(89)	(130)
Cash, cash equivalents, and restricted cash at beginning of year			197	328
Cash, cash equivalents, and restricted cash at end of the period	108	198	108	198
As Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash, cash equivalents, and restricted cash		198		328			198
Operating Revenues
Mileage plan other revenue		128		247
Total Operating Revenues		2,102		3,851
Operating Expenses
Wages and benefits		469		917
Selling expenses		97		178
Special items—merger-related costs		24		64
All other operating expenses		1,019		2,030
Total Operating Expenses		1,609		3,189
Operating Income		493		662
Nonoperating Income (Expense)
Other—net		(1)		(4)
Nonoperating Income (Expense), Other		(13)		(27)
Nonoperating Income (Expense) Total		(14)		(31)
Income Before Income Tax		479		631
Income tax expense		183		236
Net Income (loss)		296		395
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization				180
Stock-based compensation and other				25
Changes in deferred tax provision				132
Increase in air traffic liability				406
Increase in deferred revenue				15
Other—net				(69)
Net cash provided by operating activities				1,084
Net cash used in investing activities				(971)
Net cash used in financing activities				(243)
Net increase (decrease) in cash, cash equivalents, and restricted cash				(130)
Cash, cash equivalents, and restricted cash at beginning of year				328
Cash, cash equivalents, and restricted cash at end of the period		198		198
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		(19)		(38)
Total Operating Revenues		0		(9)
Operating Expenses
Wages and benefits		0		0
Selling expenses		5		7
Special items—merger-related costs		0		(1)
All other operating expenses		0		0
Total Operating Expenses		5		6
Operating Income		(5)		(15)
Nonoperating Income (Expense)
Other—net		0		0
Nonoperating Income (Expense), Other		0		0
Nonoperating Income (Expense) Total		0		0
Income Before Income Tax		(5)		(15)
Income tax expense		(2)		(6)
Net Income (loss)		(3)		(9)
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				(5)
Increase in air traffic liability				(22)
Increase in deferred revenue				54
Other—net				(18)
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		1		3
Selling expenses		0		0
Special items—merger-related costs		0		0
All other operating expenses		0		0
Total Operating Expenses		1		3
Operating Income		(1)		(3)
Nonoperating Income (Expense)
Other—net		1		3
Nonoperating Income (Expense), Other		0		0
Nonoperating Income (Expense) Total		1		3
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	51	48	91	86
Cargo and Freight [Member] | As Reported [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes		167		313
Cargo and Freight [Member] | Accounting Standards Update 2014-09 [Member] | Adjustments [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes		(119)		(227)
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	1,997	1,945	3,682	3,547
Passenger [Member] | As Reported [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes		1,807		3,291
Passenger [Member] | Accounting Standards Update 2014-09 [Member] | Adjustments [Member]
Operating Revenues
Revenue from contract with customer, including assessed taxes		138		256
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	51	48	91	86
Cargo and Other Revenue [Member] | Cargo and Freight [Member]
Operating Revenues
Revenue from Contract with Customer, Excluding Assessed Tax	$ 51	$ 48	$ 91	$ 86