Operations and summary of significant accounting policies (Details 4) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt issuance costs, net		$ 80
Prepaid expenses and other current assets	$ 1,682	1,662
Noncurrent deferred and refundable income taxes	2,790	2,489
Other current liabilities	1,635	1,671
Other liabilities	3,184	$ 3,203
New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred and refundable income taxes	(910)
Prepaid expenses and other current assets	616
Noncurrent deferred and refundable income taxes	835
Other current liabilities	(59)
Other liabilities	$ (16)