Revenue (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Taxes other than on income	[1]	$ 1,259	$ 3,213	$ 3,966	$ 9,149
Includes excise, value-added and similar taxes			$ 1,867		$ 5,315
Receivables		$ 11,900		11,900		$ 9,800
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Taxes other than on income				$ 5,900

[1] The three-month and nine-month comparative periods ended September 30, 2017, include excise, value-added and similar taxes of $1,867 million and $5,315 million, respectively, collected on behalf of third parties. Beginning in 2018, these taxes are netted in "Taxes other than on income" in accordance with ASU 2014-09. Refer to Note 17, "Revenue" beginning on page 24.