Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

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Derivatives and Risk Management - Hedge Position (Details) € in Millions, ¥ in Millions, gal in Millions, $ in Millions, $ in Millions	Mar. 31, 2018 EUR (€) gal	Mar. 31, 2018 JPY (¥) gal	Mar. 31, 2018 CAD ($) gal	Mar. 31, 2018 USD ($) gal	Jan. 31, 2018 EUR (€)	Dec. 31, 2017 JPY (¥) gal	Dec. 31, 2017 CAD ($) gal	Dec. 31, 2017 USD ($) gal
Derivatives, Fair Value
Total derivative contracts, net				$ (35)				$ (83)
Prepaid Expenses and Other
Derivatives, Fair Value
Total derivative contracts, assets				1,009				639
Other Noncurrent Assets
Derivatives, Fair Value
Total derivative contracts, assets				54				9
Other Accrued Liabilities
Derivatives, Fair Value
Total derivative contracts, liabilities				(1,020)				(707)
Other Noncurrent Liabilities
Derivatives, Fair Value
Total derivative contracts, liabilities				(78)				(24)
Foreign currency exchange contracts \| Designated as hedging instrument
Derivatives, Fair Value
Foreign currency exchange contracts, hedge derivatives, net				(16)				(17)
Foreign currency exchange contracts \| Designated as hedging instrument \| Prepaid Expenses and Other
Derivatives, Fair Value
Foreign currency exchange contracts, assets				1				1
Foreign currency exchange contracts \| Designated as hedging instrument \| Other Noncurrent Assets
Derivatives, Fair Value
Foreign currency exchange contracts, assets				1				1
Foreign currency exchange contracts \| Designated as hedging instrument \| Other Accrued Liabilities
Derivatives, Fair Value
Foreign currency exchange contracts, liabilities				(14)				(13)
Foreign currency exchange contracts \| Designated as hedging instrument \| Other Noncurrent Liabilities
Derivatives, Fair Value
Foreign currency exchange contracts, liabilities				(4)				$ (6)
Foreign currency exchange contracts \| Not designated as hedging instrument
Derivatives, Fair Value
Derivative, notional amount \| €	€ 375
Foreign currency exchange contracts, hedge derivatives, net				(16)
Foreign currency exchange contracts \| Not designated as hedging instrument \| Prepaid Expenses and Other
Derivatives, Fair Value
Foreign currency exchange contracts, assets				7
Foreign currency exchange contracts \| Not designated as hedging instrument \| Other Noncurrent Assets
Derivatives, Fair Value
Foreign currency exchange contracts, assets				0
Foreign currency exchange contracts \| Not designated as hedging instrument \| Other Accrued Liabilities
Derivatives, Fair Value
Foreign currency exchange contracts, liabilities				0
Foreign currency exchange contracts \| Not designated as hedging instrument \| Other Noncurrent Liabilities
Derivatives, Fair Value
Foreign currency exchange contracts, liabilities				$ (23)
Fuel hedge contracts \| Not designated as hedging instrument
Derivatives, Fair Value
Derivative, nonmonetary notional amount \| gal	267	267	267	267		249	249	249
Fuel hedge contracts, derivatives, net				$ (3)				$ (66)
Fuel hedge contracts \| Not designated as hedging instrument \| Prepaid Expenses and Other
Derivatives, Fair Value
Fuel hedge contracts, assets				1,001				638
Fuel hedge contracts \| Not designated as hedging instrument \| Other Noncurrent Assets
Derivatives, Fair Value
Fuel hedge contracts, assets				53				8
Fuel hedge contracts \| Not designated as hedging instrument \| Other Accrued Liabilities
Derivatives, Fair Value
Fuel hedge contracts, liabilities				(1,006)				(694)
Fuel hedge contracts \| Not designated as hedging instrument \| Other Noncurrent Liabilities
Derivatives, Fair Value
Fuel hedge contracts, liabilities				$ (51)				$ (18)
Cash flow hedging \| Foreign currency exchange contracts \| Designated as hedging instrument
Derivatives, Fair Value
Derivative, notional amount		¥ 18,701	$ 166			¥ 23,512	$ 490
Cash flow hedging \| Foreign currency exchange contracts \| Not designated as hedging instrument
Derivatives, Fair Value
Derivative, notional amount \| €					€ 375