Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Schedule of assets (liabilities) measured at fair value on a recurring basis

	December 31, 2020								Valuation Technique
(in millions)	Total		Level 1		Level 2		Level 3
Cash equivalents	$	5,755	$	5,755	$	—	$	—	(a)
Restricted cash equivalents	1,747		1,747		—		—		(a)
Short-term investments
U.S. Government securities	5,789		3,919		1,870		—		(a)
Long-term investments	1,417		948		38		431		(a)(b)
Hedge derivatives, net
Fuel hedge contracts	(9)		—		(9)		—		(a)(b)
Interest rate contracts	23		—		23		—		(a)
Foreign currency exchange contracts	(13)		—		(13)		—		(a)

	December 31, 2019								Valuation Technique
(in millions)	Total		Level 1		Level 2		Level 3
Cash equivalents	$	586	$	586	$	—	$	—	(a)
Restricted cash equivalents	847		847		—		—		(a)
Long-term investments	1,099		881		33		185		(a)(b)
Hedge derivatives, net
Fuel hedge contracts	1		(1)		2		—		(a)(b)
Interest rate contracts	61		—		61		—		(a)
Foreign currency exchange contracts	6		—		6		—		(a)

(1)See Note 11, "Employee Benefit Plans," for fair value of benefit plan assets.