Derivatives and Risk Management - Schedule of Derivative Instruments of Financial Position (Details) ¥ in Millions, gal in Millions, CAD in Millions, $ in Millions	Dec. 31, 2016 JPY (¥) gal	Dec. 31, 2016 CAD gal	Dec. 31, 2016 USD ($) gal	Dec. 31, 2015 JPY (¥) gal	Dec. 31, 2015 CAD gal	Dec. 31, 2015 USD ($) gal
Derivatives, Fair Value [Line Items]
Foreign currency exchange contracts			$ 27			$ 94
Fuel hedge contracts, hedge derivatives, net			(324)			(672)
Net derivative contracts, hedge derivatives, net			(291)			(581)
Hedge derivative asset
Derivatives, Fair Value [Line Items]
Total derivative contracts, assets			393			1,987
Net derivative contracts, assets			31			143
Other noncurrent assets
Derivatives, Fair Value [Line Items]
Total derivative contracts, assets			7			24
Net derivative contracts, assets			6			21
Hedge derivative liability
Derivatives, Fair Value [Line Items]
Total derivative contracts, liabilities			(688)			(2,581)
Net derivative contracts, liabilities			(326)			(737)
Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Total derivative contracts, liabilities			(3)			(11)
Net derivative contracts, liabilities			(2)			(8)
Interest rate contract | Designated as hedging instrument
Derivatives, Fair Value [Line Items]
Interest rate contracts (fair value hedges), hedge derivatives, net			6			(3)
Interest rate contract | Designated as hedging instrument | Hedge derivative asset
Derivatives, Fair Value [Line Items]
Interest rate contracts (fair value hedges), assets			2			4
Interest rate contract | Designated as hedging instrument | Other noncurrent assets
Derivatives, Fair Value [Line Items]
Interest rate contracts (fair value hedges), assets			4			0
Interest rate contract | Designated as hedging instrument | Hedge derivative liability
Derivatives, Fair Value [Line Items]
Interest rate contracts (fair value hedges), liabilities			0			0
Interest rate contract | Designated as hedging instrument | Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Interest rate contracts (fair value hedges), liabilities			0			(7)
Interest rate contract | Fair value hedging | Designated as hedging instrument
Derivatives, Fair Value [Line Items]
Derivative, notional amount			349			384
Foreign currency exchange contract | Designated as hedging instrument
Derivatives, Fair Value [Line Items]
Foreign currency exchange contracts			27			94
Foreign currency exchange contract | Designated as hedging instrument | Hedge derivative asset
Derivatives, Fair Value [Line Items]
Foreign currency exchange contracts, assets			31			76
Foreign currency exchange contract | Designated as hedging instrument | Other noncurrent assets
Derivatives, Fair Value [Line Items]
Foreign currency exchange contracts, assets			3			20
Foreign currency exchange contract | Designated as hedging instrument | Hedge derivative liability
Derivatives, Fair Value [Line Items]
Foreign currency exchange contracts, liabilities			(4)			(1)
Foreign currency exchange contract | Designated as hedging instrument | Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Foreign currency exchange contracts, liabilities			$ (3)			$ (1)
Foreign currency exchange contract | Cash flow hedging | Designated as hedging instrument
Derivatives, Fair Value [Line Items]
Derivative, notional amount	¥ 54,853	CAD 335		¥ 46,920	CAD 395
Fuel hedge contract | Not designated as hedging instrument
Derivatives, Fair Value [Line Items]
Derivative, nonmonetary notional amount | gal	197	197	197	887	887	887
Fuel hedge contracts, hedge derivatives, net			$ (324)			$ (672)
Fuel hedge contract | Not designated as hedging instrument | Hedge derivative asset
Derivatives, Fair Value [Line Items]
Fuel hedge contracts, assets			360			1,907
Fuel hedge contract | Not designated as hedging instrument | Other noncurrent assets
Derivatives, Fair Value [Line Items]
Fuel hedge contracts, assets			0			4
Fuel hedge contract | Not designated as hedging instrument | Hedge derivative liability
Derivatives, Fair Value [Line Items]
Fuel hedge contracts, liabilities			(684)			(2,580)
Fuel hedge contract | Not designated as hedging instrument | Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Fuel hedge contracts, liabilities			$ 0			$ (3)