Basis of Presentation and Significant Accounting Policies - Impact of Adoption of Accounting Standards on Consolidated Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2018	[1]	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts receivable	$ 10,024		$ 8,234	$ 8,221	[1]
Inventories	8,184	[2]	7,567	7,578	[1],[2]
Current tax assets	3,686		3,036	3,050	[1]
Noncurrent deferred tax assets and other noncurrent tax assets	1,875		1,838	1,855	[1]
Other noncurrent assets	2,980		3,023	3,227	[1]
Other current liabilities	10,490		10,992	11,115	[1]
Noncurrent deferred tax liabilities	5,512		3,988	3,900	[1]
Other noncurrent liabilities	6,367		5,690	6,149	[1]
Retained earnings	91,995		86,466	85,291	[1]
Accumulated other comprehensive loss	$ (10,417)		$ (10,235)	(9,321)	[1]
As Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts receivable				8,221
Inventories				7,578
Current tax assets				3,050
Noncurrent deferred tax assets and other noncurrent tax assets				1,855
Other noncurrent assets				3,227
Other current liabilities				11,115
Noncurrent deferred tax liabilities				3,900
Other noncurrent liabilities				6,149
Retained earnings				85,291
Accumulated other comprehensive loss				(9,321)
Revenues [Member] | Effect of Change Higher/(Lower) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts receivable				13
Inventories				(11)
Current tax assets				(11)
Noncurrent deferred tax assets and other noncurrent tax assets				(17)
Other noncurrent assets				0
Other current liabilities				(123)
Noncurrent deferred tax liabilities				106
Other noncurrent liabilities				(459)
Retained earnings				450
Accumulated other comprehensive loss				0
Financial Assets and Liabilities [Member] | Effect of Change Higher/(Lower) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts receivable				0
Inventories				0
Current tax assets				0
Noncurrent deferred tax assets and other noncurrent tax assets				0
Other noncurrent assets				0
Other current liabilities				0
Noncurrent deferred tax liabilities				0
Other noncurrent liabilities				0
Retained earnings				419
Accumulated other comprehensive loss				(419)
Income Tax Accounting [Member] | Effect of Change Higher/(Lower) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts receivable				0
Inventories				0
Current tax assets				(3)
Noncurrent deferred tax assets and other noncurrent tax assets				0
Other noncurrent assets				(204)
Other current liabilities				0
Noncurrent deferred tax liabilities				(18)
Other noncurrent liabilities				0
Retained earnings				(189)
Accumulated other comprehensive loss				0
Reclassification of Certain Tax Effects from AOCI [Member] | Effect of Change Higher/(Lower) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts receivable				0
Inventories				0
Current tax assets				0
Noncurrent deferred tax assets and other noncurrent tax assets				0
Other noncurrent assets				0
Other current liabilities				0
Noncurrent deferred tax liabilities				0
Other noncurrent liabilities				0
Retained earnings				495
Accumulated other comprehensive loss				$ (495)

[1] Amounts may not add due to rounding.

[2] The change from December 31, 2017 reflects increases for certain products to meet targeted levels in the normal course of business, including inventory build for supply recovery, network strategy and new product launches, partially offset by a decrease due to foreign exchange.