Revenue Recognition - Narrative (Details) - USD ($) $ in Billions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Disaggregation of Revenue [Line Items] | |||
| Marketing contracts duration, minimum (in years) | 1 year | ||
| Marketing contracts duration, maximum (in years) | 11 years | ||
| Cash sales of miles from marketing agreements | $ 4.2 | $ 3.5 | $ 3.2 |
| Majority of new miles, redemption period (in years) | 2 years | ||
| Air traffic | |||
| Disaggregation of Revenue [Line Items] | |||
| Revenue recognized that was in prior year air traffic liability | $ 3.8 | $ 3.5 | $ 3.5 |