Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2015

Fair Value Disclosures [Abstract]

Schedule of Assets (Liabilities) Measured at Fair Value on a Recurring Basis

Assets (Liabilities) Measured at Fair Value on a Recurring Basis⁽¹⁾ 

	December 31, 2015								Valuation Technique
(in millions)	Total			Level 1		Level 2
Cash equivalents	$	1,543		$	1,543	$	—		(a)
Short-term investments
U.S. government and agency securities	151			74		77			(a)
Asset- and mortgage-backed securities	380			—		380			(a)
Corporate obligations	896			—		896			(a)
Other fixed income securities	38			—		38			(a)
Restricted cash equivalents and investments	49			49		—			(a)
Long-term investments	155			130		25			(a)
Hedge derivatives, net
Fuel hedge contracts	(672		)	65		(737		)	(a)(b)
Interest rate contract	(3		)	—		(3		)	(a)(b)
Foreign currency exchange contracts	94			—		94			(a)

	December 31, 2014									Valuation Technique
(in millions)	Total			Level 1			Level 2
Cash equivalents	$	1,612		$	1,612		$	—		(a)
Short-term investments
U.S. government securities	59			—			59			(a)
Asset- and mortgage-backed securities	392			—			392			(a)
Corporate obligations	749			—			749			(a)
Other fixed income securities	17			—			17			(a)
Restricted cash equivalents and investments	37			37			—			(a)
Long-term investments	118			90			28			(a)
Hedge derivatives, net
Fuel hedge contracts	(1,848		)	(167		)	(1,681		)	(a)(b)
Interest rate contract	(7		)	—			(7		)	(a)(b)
Foreign currency exchange contracts	73			—			73			(a)

⁽¹⁾  See Note 9, “Employee Benefit Plans,” for fair value of benefit plan assets.