Revenues from Contracts with Customers - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) segments	Sep. 30, 2018 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)
Disaggregation of Revenue [Line Items]
Number of Reportable Segments | segments			2
Total revenue	$ 7,795	$ 8,433	$ 15,937	$ 16,558
Revenue, Remaining Performance Obligation, Amount	8,609		8,609
Equipment sales
Disaggregation of Revenue [Line Items]
Total revenue	$ 1,192	$ 1,418	$ 2,412	$ 2,591
Scenario, Forecast [Member]
Disaggregation of Revenue [Line Items]
Revenue, Remaining Performance Obligation, Amount					$ 1,300	$ 1,700