Revenue Recognition - Transition Disclosures, Statement of Cash Flows (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net income	$ 4,083	$ 4,082
Adjustments to reconcile net income to cash provided by operating activities
Changes in operating assets and liabilities, net of acquisitions/divestitures	336	785
Net cash provided by operating activities	6,896	$ 7,421
Accounting Standards Update 2014-09, Revenue from Contracts with Customers | Adjustments to convert to prior GAAP
Cash flows from operating activities:
Net income	(7)
Adjustments to reconcile net income to cash provided by operating activities
Changes in operating assets and liabilities, net of acquisitions/divestitures	7
Accounting Standards Update 2014-09, Revenue from Contracts with Customers | Adjusted amounts under prior GAAP
Cash flows from operating activities:
Net income	4,076
Adjustments to reconcile net income to cash provided by operating activities
Changes in operating assets and liabilities, net of acquisitions/divestitures	343
Net cash provided by operating activities	$ 6,896