Derivatives - Hedge Position (Details) ¥ in Millions, gal in Millions, CAD in Millions, $ in Millions	Sep. 30, 2016 JPY (¥) gal	Sep. 30, 2016 CAD gal	Sep. 30, 2016 USD ($) gal	Dec. 31, 2015 JPY (¥) gal	Dec. 31, 2015 CAD gal	Dec. 31, 2015 USD ($) gal
Derivatives, Fair Value
Foreign currency exchange contracts, hedge derivatives, net			$ (64)			$ 94
Fuel hedge contracts, derivatives, net			(271)			(672)
Net derivative contracts, hedge derivatives, net			(327)			(581)
Hedge Derivatives Asset
Derivatives, Fair Value
Total derivative contracts, assets			496			1,987
Other Noncurrent Assets
Derivatives, Fair Value
Total derivative contracts, assets			46			24
Hedge Derivatives Liability
Derivatives, Fair Value
Total derivative contracts, liabilities			(724)			(2,581)
Other Noncurrent Liabilities
Derivatives, Fair Value
Total derivative contracts, liabilities			(145)			(11)
Designated as hedging instrument
Derivatives, Fair Value
Interest rate contract (fair value hedge), hedge derivatives, net			8			(3)
Foreign currency exchange contracts, hedge derivatives, net			(64)			94
Not designated as hedging instrument
Derivatives, Fair Value
Fuel hedge contracts, derivatives, net			(271)			(672)
Interest rate contract (fair value hedge) | Designated as hedging instrument | Hedge Derivatives Asset
Derivatives, Fair Value
Interest rate contract (fair value hedge), assets			3			4
Interest rate contract (fair value hedge) | Designated as hedging instrument | Other Noncurrent Assets
Derivatives, Fair Value
Interest rate contract (fair value hedge), assets			5			0
Interest rate contract (fair value hedge) | Designated as hedging instrument | Hedge Derivatives Liability
Derivatives, Fair Value
Interest rate contract (fair value hedge), liabilities			0			0
Interest rate contract (fair value hedge) | Designated as hedging instrument | Other Noncurrent Liabilities
Derivatives, Fair Value
Interest rate contract (fair value hedge), liabilities			0			(7)
Foreign currency exchange contracts | Designated as hedging instrument | Hedge Derivatives Asset
Derivatives, Fair Value
Foreign currency exchange contracts, assets			10			76
Foreign currency exchange contracts | Designated as hedging instrument | Other Noncurrent Assets
Derivatives, Fair Value
Foreign currency exchange contracts, assets			2			20
Foreign currency exchange contracts | Designated as hedging instrument | Hedge Derivatives Liability
Derivatives, Fair Value
Foreign currency exchange contracts, liabilities			(44)			(1)
Foreign currency exchange contracts | Designated as hedging instrument | Other Noncurrent Liabilities
Derivatives, Fair Value
Foreign currency exchange contracts, liabilities			$ (32)			$ (1)
Fuel hedge contracts | Not designated as hedging instrument
Derivatives, Fair Value
Derivative, nonmonetary notional amount | gal	179	179	179	887	887	887
Fuel hedge contracts | Not designated as hedging instrument | Hedge Derivatives Asset
Derivatives, Fair Value
Fuel hedge contracts, assets			$ 483			$ 1,907
Fuel hedge contracts | Not designated as hedging instrument | Other Noncurrent Assets
Derivatives, Fair Value
Fuel hedge contracts, assets			39			4
Fuel hedge contracts | Not designated as hedging instrument | Hedge Derivatives Liability
Derivatives, Fair Value
Fuel hedge contracts, liabilities			(680)			(2,580)
Fuel hedge contracts | Not designated as hedging instrument | Other Noncurrent Liabilities
Derivatives, Fair Value
Fuel hedge contracts, liabilities			(113)			(3)
Fair value hedging | Interest rate contract (fair value hedge) | Designated as hedging instrument
Derivatives, Fair Value
Derivative, notional amount			$ 349			$ 384
Cash flow hedging | Foreign currency exchange contracts | Designated as hedging instrument
Derivatives, Fair Value
Derivative, notional amount	¥ 60,509	CAD 396		¥ 46,920	CAD 395