Combined Notes to the Financial Statements (Unaudited) (Details)		3 Months Ended
	Jan. 15, 2021 USD ($)	Jun. 30, 2021	Mar. 31, 2021 USD ($) employee	Mar. 31, 2020 USD ($)	Apr. 22, 2021 USD ($) $ / shares shares	Apr. 21, 2021 USD ($)
Unusual or Infrequent Item, or Both [Line Items]
Percent of capacity cut			(54.00%)
Proceeds from issuance of debt, net of discounts and fees			$ 1,336,000,000	$ 2,813,000,000
Proceeds from the issuance of common stock			$ 500,000,000
PSP2
Unusual or Infrequent Item, or Both [Line Items]
Total funding provided under the Payroll Support Program	$ 2,600,000,000
Funding provided through direct grants under the Payroll Support Program	1,900,000,000
Forecast
Unusual or Infrequent Item, or Both [Line Items]
Percent of capacity cut		45.00%
Forecast | PSP2
Unusual or Infrequent Item, or Both [Line Items]
Additional amount expected to be received					$ 391,000,000
Forecast | PSP3
Unusual or Infrequent Item, or Both [Line Items]
Additional amount expected to be received					$ 2,800,000,000
Number of securities called by warrants (in shares) | shares					1,500,000
Warrant exercise price (in dollars per share) | $ / shares					$ 53.92
Voluntary Separation Leave Programs | Employee Separation
Unusual or Infrequent Item, or Both [Line Items]
Number of employees electing to voluntarily separate from the company | employee			4,500
PSP3 Note | Forecast | PSP3
Unusual or Infrequent Item, or Both [Line Items]
Additional amount expected to be received through loans					$ 800,000,000
Notes, Secured Term Loans and Aircraft Financing
Unusual or Infrequent Item, or Both [Line Items]
Proceeds from issuance of debt, net of discounts and fees			$ 1,400,000,000
Unsecured Debt | PSP2 Note
Unusual or Infrequent Item, or Both [Line Items]
Term of debt			10 years
Face amount			$ 753,000,000
Unsecured Debt | PSP2 Note | PSP2
Unusual or Infrequent Item, or Both [Line Items]
Funding provided through loans under the Payroll Support Program	$ 753,000,000
Term of debt	10 years
Unsecured Debt | PSP2 Note | Forecast | PSP2
Unusual or Infrequent Item, or Both [Line Items]
Additional amount expected to be received through loans					$ 117,000,000
Secured Debt | 2026 Notes and 2029 Notes | Subsequent Event
Unusual or Infrequent Item, or Both [Line Items]
Face amount						$ 4,000,000,000.0
Secured Debt | 2026 Notes | Subsequent Event
Unusual or Infrequent Item, or Both [Line Items]
Face amount						$ 2,000,000,000.0
Stated interest rate						4.375%
Secured Debt | 2029 Notes | Subsequent Event
Unusual or Infrequent Item, or Both [Line Items]
Face amount						$ 2,000,000,000.0
Stated interest rate						4.625%
Secured Debt | Term Loan B Facility due 2028 | Subsequent Event
Unusual or Infrequent Item, or Both [Line Items]
Face amount						$ 5,000,000,000.0
Secured Debt | Senior Secured Revolving Credit Facility due 2025 | Revolving Credit Facility | Subsequent Event
Unusual or Infrequent Item, or Both [Line Items]
Maximum borrowing capacity						1,750,000,000
Secured Debt | Term Loan Facility | Subsequent Event
Unusual or Infrequent Item, or Both [Line Items]
Face amount						1,400,000,000
Secured Debt | Credit Agreement | Revolving Credit Facility | Subsequent Event
Unusual or Infrequent Item, or Both [Line Items]
Face amount						1,000,000,000.0
Secured Debt | CARES Act Term Loan Facility | Subsequent Event
Unusual or Infrequent Item, or Both [Line Items]
Face amount						$ 520,000,000