Investments - Fair Value Investments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value Investments
Carrying value	$ 1,417	$ 1,099
Hanjin-KAL
Fair Value Investments
Ownership interest (percent)	13.00%	10.00%
Carrying value	$ 512	$ 205
Air France-KLM
Fair Value Investments
Ownership interest (percent)	9.00%	9.00%
Carrying value	$ 235	$ 418
China Eastern
Fair Value Investments
Ownership interest (percent)	3.00%	3.00%
Carrying value	$ 201	$ 258
Other Investments
Fair Value Investments
Carrying value	$ 469	$ 218