Employee Benefit Plans - Benefit Plan Assets Measured at Fair Value on Recurring Basis (Details) - Recurring - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Benefit plan assets by asset class
Benefit plan assets	$ 16,328	$ 13,721
Level 1 and Level 2
Benefit plan assets by asset class
Benefit plan assets	6,474	4,585
Level 1 and Level 2 | Equities and equity-related instruments
Benefit plan assets by asset class
Benefit plan assets	889	500
Level 1 and Level 2 | Delta common stock
Benefit plan assets by asset class
Benefit plan assets	737	675
Level 1 and Level 2 | Cash equivalents
Benefit plan assets by asset class
Benefit plan assets	1,279	1,020
Level 1 and Level 2 | Fixed income and fixed income-related instruments
Benefit plan assets by asset class
Benefit plan assets	3,569	2,390
Level 1
Benefit plan assets by asset class
Benefit plan assets	2,001	1,620
Level 1 | Equities and equity-related instruments
Benefit plan assets by asset class
Benefit plan assets	840	400
Level 1 | Delta common stock
Benefit plan assets by asset class
Benefit plan assets	737	675
Level 1 | Cash equivalents
Benefit plan assets by asset class
Benefit plan assets	327	312
Level 1 | Fixed income and fixed income-related instruments
Benefit plan assets by asset class
Benefit plan assets	97	233
Level 2
Benefit plan assets by asset class
Benefit plan assets	4,473	2,965
Level 2 | Equities and equity-related instruments
Benefit plan assets by asset class
Benefit plan assets	49	100
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	952	708
Level 2 | Fixed income and fixed income-related instruments
Benefit plan assets by asset class
Benefit plan assets	3,472	2,157
NAV
Benefit plan assets by asset class
Benefit plan assets	$ 9,854	$ 9,136