Employee Benefit Plans - Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Defined benefit plans:
Service cost		$ 2	$ 2	$ 3
Interest cost		615	703	674
Expected return on assets		(1,010)	(815)	(905)
Special termination benefits		0	0	0
Settlements		12	0	0
Amortization of:
Prior service cost (benefit)		30	28	28
Unrecognized net loss (gain)		164	150	141
Net periodic benefit cost (income)		(187)	68	(59)
Retiree Medical and  Other Postretirement Benefits
Defined benefit plans:
Service cost		8	3	5
Interest cost		30	33	35
Expected return on assets		(11)	(15)	(24)
Special termination benefits	$ 410	410	0	0
Settlements		0	0	0
Amortization of:
Prior service cost (benefit)		(135)	(236)	(236)
Unrecognized net loss (gain)		(24)	(31)	(21)
Net periodic benefit cost (income)		278	(246)	(241)
American Airlines, Inc. | Pension Benefits
Defined benefit plans:
Service cost		2	2	2
Interest cost		611	699	670
Expected return on assets		(1,005)	(811)	(901)
Special termination benefits		0	0	0
Settlements		12	0	0
Amortization of:
Prior service cost (benefit)		29	28	28
Unrecognized net loss (gain)		164	150	140
Net periodic benefit cost (income)		(187)	68	(61)
American Airlines, Inc. | Retiree Medical and  Other Postretirement Benefits
Defined benefit plans:
Service cost		8	3	5
Interest cost		30	33	35
Expected return on assets		(11)	(15)	(24)
Special termination benefits	$ 410	410	0	0
Settlements		0		0
Amortization of:
Prior service cost (benefit)		(135)	(236)	(236)
Unrecognized net loss (gain)		(24)	(31)	(21)
Net periodic benefit cost (income)		$ 278	$ (246)	$ (241)