Pensions - Schedule of significant weighted average assumptions (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Discount rate for calculating net periodic benefit costs (as a percent)	3.85%	3.70%	4.50%
Expected long-term rate of return on plan assets (as a percent(	4.90%	4.10%	4.80%
Discount rate for calculating benefit obligation (as a percent)	2.70%	3.85%