Revenue (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Taxes other than on income	[1]	$ 1,363	$ 3,065	$ 2,707	$ 5,936
Includes excise, value-added and similar taxes			$ 1,771		$ 3,448
Performance obligation		30 days		30 days
Receivables		$ 11,200		$ 11,200		$ 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				$ 3,900

[1] The three-month and six-month comparative periods ended June 30, 2017, include excise, value-added and similar taxes of $1,771 million and $3,448 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.