Summary of significant accounting policies - Property, plant and equipment (Details)	12 Months Ended
	Dec. 31, 2016
Buildings
Property, Plant and Equipment [Line Items]
Residual value, percentage	10.00%
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Useful life (in years)	60 years
Trains | Maximum
Property, Plant and Equipment [Line Items]
Useful life (in years)	75 years
River cruise ship and canal boats
Property, Plant and Equipment [Line Items]
Useful life (in years)	25 years
Furniture, fixtures and equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life (in years)	25 years
Furniture, fixtures and equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life (in years)	3 years