Employee Benefit Plans - Changes in Fair Value Measurements of Level 3 Investments (Details) - Pension Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Change in fair value measurements of level 3 investments
Fair value of plan assets at beginning of period	$ 12,897	$ 10,053
Fair value of plan assets at end of period	13,557	12,897
Level 3     | Private Market Partnerships
Change in fair value measurements of level 3 investments
Fair value of plan assets at beginning of period	10	7
Relating to assets still held at the reporting date	1
Purchases	4	3
Fair value of plan assets at end of period	15	10
Level 3     | Insurance Group Annuity Contracts
Change in fair value measurements of level 3 investments
Fair value of plan assets at beginning of period	2	2
Relating to assets still held at the reporting date	0
Purchases	0	0
Fair value of plan assets at end of period	2	2
American Airlines, Inc.
Change in fair value measurements of level 3 investments
Fair value of plan assets at beginning of period	12,829	10,001
Fair value of plan assets at end of period	13,477	12,829
American Airlines, Inc. | Level 3     | Private Market Partnerships
Change in fair value measurements of level 3 investments
Fair value of plan assets at beginning of period	10	7
Relating to assets still held at the reporting date	1
Purchases	4	3
Fair value of plan assets at end of period	15	10
American Airlines, Inc. | Level 3     | Insurance Group Annuity Contracts
Change in fair value measurements of level 3 investments
Fair value of plan assets at beginning of period	2	2
Relating to assets still held at the reporting date	0
Purchases	0	0
Fair value of plan assets at end of period	$ 2	$ 2