Employee benefit plans - Health Care Cost Trend Rates Related to U.S. Plan (Details)	Dec. 31, 2019	Dec. 31, 2018
Pre-age 65
Defined Benefit Plan Disclosure [Line Items]
Healthcare Cost Trend Rate	6.25%	6.50%
Ultimate Trend Rate	4.50%	4.50%
Post-age 65
Defined Benefit Plan Disclosure [Line Items]
Healthcare Cost Trend Rate	6.25%	6.50%
Ultimate Trend Rate	4.50%	4.50%