Revenue Recognition - Transition Disclosures, Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income	$ 1,679	$ 1,750
Adjustments to reconcile net income to cash provided by operating activities
Changes in operating assets and liabilities, net of acquisitions/divestitures	1,658	964
Net cash provided by operating activities	4,602	$ 3,955
Accounting Standards Update 2014-09, Revenue from Contracts with Customers | Adjustments to convert to prior GAAP
Cash flows from operating activities:
Net income	(5)
Adjustments to reconcile net income to cash provided by operating activities
Changes in operating assets and liabilities, net of acquisitions/divestitures	5
Accounting Standards Update 2014-09, Revenue from Contracts with Customers | Adjusted amounts under prior GAAP
Cash flows from operating activities:
Net income	1,674
Adjustments to reconcile net income to cash provided by operating activities
Changes in operating assets and liabilities, net of acquisitions/divestitures	1,663
Net cash provided by operating activities	$ 4,602