Deferred revenues - Remaining Performance Obligation (Details) $ in Billions	Sep. 30, 2020 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contracted not recognized revenue	$ 1.9
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contracted not recognized revenue	$ 1.4
Contracted not recognized revenue, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contracted not recognized revenue	$ 0.4
Contracted not recognized revenue, period	1 year