Income taxes - Reconciliation items from U.S. statutory income tax rate to the effective tax rate (Details)		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
U.S. statutory income tax rate		35.00%	35.00%	35.00%
Non-U.S. effective tax rates		(3.70%)	(4.00%)	(5.50%)
U.S. excess tax benefit for stock compensation	[1]	(3.00%)	(0.00%)	(0.00%)
U.S. tax benefit for manufacturing		(1.50%)	(1.60%)	(1.30%)
U.S. R&D tax credit		(1.20%)	(1.30%)	(1.50%)
U.S. non-deductible expenses		0.30%	0.30%	0.20%
Impact of changes to uncertain tax positions		0.60%	0.20%	0.10%
Other		0.60%	0.60%	0.20%
Effective tax rate		27.10%	29.20%	27.20%

[1] This is related to the adoption of ASU 2016-09 as discussed in Note 2.