Remaining Unsatisfied Performance Obligations - Schedule of remaining performance obligation (Details) $ in Millions	Sep. 30, 2019 USD ($)
Revenue from Contract with Customer [Abstract]
Remaining performance obligation	$ 28,029
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligation	11,967
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligation	10,116
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-10-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligation	$ 5,946