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