Employee Benefit Plans - Benefit Plan Assets Measured at Fair Value on Recurring Basis (Details) - Recurring - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Benefit plan assets by asset class
Benefit plan assets	$ 16,600	$ 16,328
Level 1 and Level 2
Benefit plan assets by asset class
Benefit plan assets	6,173	6,474
Level 1 and Level 2 | Equities and equity-related instruments
Benefit plan assets by asset class
Benefit plan assets	1,120	889
Level 1 and Level 2 | Delta common stock
Benefit plan assets by asset class
Benefit plan assets	507	737
Level 1 and Level 2 | Cash equivalents
Benefit plan assets by asset class
Benefit plan assets	3,664	1,279
Level 1 and Level 2 | Fixed income and fixed income-related instruments
Benefit plan assets by asset class
Benefit plan assets	882	3,569
Level 1
Benefit plan assets by asset class
Benefit plan assets	1,873	2,001
Level 1 | Equities and equity-related instruments
Benefit plan assets by asset class
Benefit plan assets	1,061	840
Level 1 | Delta common stock
Benefit plan assets by asset class
Benefit plan assets	507	737
Level 1 | Cash equivalents
Benefit plan assets by asset class
Benefit plan assets	305	327
Level 1 | Fixed income and fixed income-related instruments
Benefit plan assets by asset class
Benefit plan assets	0	97
Level 2
Benefit plan assets by asset class
Benefit plan assets	4,300	4,473
Level 2 | Equities and equity-related instruments
Benefit plan assets by asset class
Benefit plan assets	59	49
Level 2 | Delta common stock
Benefit plan assets by asset class
Benefit plan assets	0	0
Level 2 | Cash equivalents
Benefit plan assets by asset class
Benefit plan assets	3,359	952
Level 2 | Fixed income and fixed income-related instruments
Benefit plan assets by asset class
Benefit plan assets	882	3,472
NAV
Benefit plan assets by asset class
Benefit plan assets	$ 10,427	$ 9,854