Derivatives - Hedge Position (Details) ¥ in Millions, gal in Millions, CAD in Millions, $ in Millions	Sep. 30, 2015 JPY (¥) gal	Sep. 30, 2015 CAD gal	Sep. 30, 2015 USD ($) gal	Dec. 31, 2014 JPY (¥) gal	Dec. 31, 2014 CAD gal	Dec. 31, 2014 USD ($) gal
Derivatives, Fair Value [Line Items]
Foreign currency exchange contracts, hedge derivatives, net			$ 92			$ 73
Fuel hedge contracts, derivatives, net			(835)			(1,848)
Net derivative contracts, hedge derivatives, net			(742)			(1,782)
Hedge Derivatives Asset
Derivatives, Fair Value [Line Items]
Total derivative contracts, assets			1,586			1,078
Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Total derivative contracts, assets			384			52
Hedge Derivatives Liability
Derivatives, Fair Value [Line Items]
Total derivative contracts, liabilities			(2,194)			(2,772)
Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Total derivative contracts, liabilities			(518)			(140)
Designated as hedging instrument
Derivatives, Fair Value [Line Items]
Interest rate contract (fair value hedge), hedge derivatives, net			1			(7)
Foreign currency exchange contracts, hedge derivatives, net			92			73
Designated as hedging instrument | Hedge Derivatives Asset
Derivatives, Fair Value [Line Items]
Interest rate contract (fair value hedge), assets			4			5
Foreign currency exchange contracts, assets			67			25
Designated as hedging instrument | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Interest rate contract (fair value hedge), assets			0			0
Foreign currency exchange contracts, assets			26			49
Designated as hedging instrument | Hedge Derivatives Liability
Derivatives, Fair Value [Line Items]
Interest rate contract (fair value hedge), liabilities			0			0
Foreign currency exchange contracts, liabilities			0			(1)
Designated as hedging instrument | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Interest rate contract (fair value hedge), liabilities			(3)			(12)
Foreign currency exchange contracts, liabilities			(1)			0
Not designated as hedging instrument
Derivatives, Fair Value [Line Items]
Fuel hedge contracts, derivatives, net			(835)			(1,848)
Not designated as hedging instrument | Hedge Derivatives Asset
Derivatives, Fair Value [Line Items]
Fuel hedge contracts, assets			1,515			1,048
Not designated as hedging instrument | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Fuel hedge contracts, assets			358			3
Not designated as hedging instrument | Hedge Derivatives Liability
Derivatives, Fair Value [Line Items]
Fuel hedge contracts, liabilities			(2,194)			(2,771)
Not designated as hedging instrument | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Fuel hedge contracts, liabilities			$ (514)			$ (128)
Fuel hedge contracts | Not designated as hedging instrument
Derivatives, Fair Value [Line Items]
Derivative, nonmonetary notional amount | gal	921	921	921	3,286	3,286	3,286
Fair value hedging | Interest rate contract (fair value hedge) | Designated as hedging instrument
Derivatives, Fair Value [Line Items]
Derivative, notional amount			$ 384			$ 416
Cash flow hedging | Foreign currency exchange contracts | Designated as hedging instrument
Derivatives, Fair Value [Line Items]
Derivative, notional amount	¥ 57,545	CAD 427		¥ 77,576	CAD 511