Summary of significant accounting policies - Property, plant and equipment (Details)	12 Months Ended
	Dec. 31, 2019
Land improvements
Significant accounting policies
Estimated useful life	20 years
Buildings | Minimum
Significant accounting policies
Estimated useful life	7 years
Buildings | Maximum
Significant accounting policies
Estimated useful life	45 years
Equipment | Minimum
Significant accounting policies
Estimated useful life	2 years
Equipment | Maximum
Significant accounting policies
Estimated useful life	40 years
Satellites | Minimum
Significant accounting policies
Estimated useful life	11 years 6 months
Satellites | Maximum
Significant accounting policies
Estimated useful life	14 years
Furniture and fixtures | Minimum
Significant accounting policies
Estimated useful life	2 years
Furniture and fixtures | Maximum
Significant accounting policies
Estimated useful life	10 years
Computer hardware | Minimum
Significant accounting policies
Estimated useful life	2 years
Computer hardware | Maximum
Significant accounting policies
Estimated useful life	13 years