WORLDWIDE PANDEMIC - Narrative (Details) $ / shares in Units, $ in Millions			3 Months Ended		6 Months Ended
	Mar. 31, 2022 USD ($) aircraft employee $ / shares	Jun. 01, 2020 employee	Mar. 31, 2022 USD ($) employee aircraft $ / shares	Mar. 31, 2021 USD ($)	Jun. 30, 2021 USD ($)
Unusual or Infrequent Item, or Both [Line Items]
Employees who elected conversion in extended emergency time off | employee			0
COVID - 19
Unusual or Infrequent Item, or Both [Line Items]
Voluntary separation program 2020 participants | employee	4,200		4,200
Number of employees who participated in extended emergency time off during 2020 | employee		12,000
Extended emergency time off accrual for employees who accepted through 2020 | $	$ 296		$ 32		$ 1,400
Extended emergency time off reversal for employees who accepted through March 31, 2021 | $			$ 115
Aircrafts in long-term storage | aircraft	4		4
Proceeds from PSP2 payroll support program | $				$ 1,200
COVID - 19 | Minimum
Unusual or Infrequent Item, or Both [Line Items]
Extended emergency time off, period		6 months
COVID - 19 | Maximum
Unusual or Infrequent Item, or Both [Line Items]
Extended emergency time off, period		18 months
COVID - 19 | Maximum | Pilots
Unusual or Infrequent Item, or Both [Line Items]
Extended emergency time off, period		5 years
United States Department of Treasury | PSP1
Unusual or Infrequent Item, or Both [Line Items]
Strike price (in USD per share) | $ / shares	$ 36.47		$ 36.47
United States Department of Treasury | PSP2
Unusual or Infrequent Item, or Both [Line Items]
Strike price (in USD per share) | $ / shares	46.28		$ 46.28
Expiration period (in years)			5 years
United States Department of Treasury | PSP3
Unusual or Infrequent Item, or Both [Line Items]
Strike price (in USD per share) | $ / shares	$ 58.51		$ 58.51
Expiration period (in years)			5 years