Restructuring and asset impairment charges (Details)	12 Months Ended
Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Document Period End Date	Dec. 31, 2016

The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD.

No definition available.

Name:	dei_DocumentPeriodEndDate
Namespace Prefix:	dei_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration