New Accounting Guidance (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements
Prepaid expenses and other current assets	$ 1,777	$ 1,682
Noncurrent deferred and refundable income taxes	2,940	2,790
Other current liabilities	(1,641)	(1,635)
Other liabilities	$ (3,238)	$ (3,184)