Segment and Geographic Information - Geographic PPE (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Property and Equipment, net		$ 3,363
United States
Segment Reporting Information [Line Items]
Property and Equipment, net	$ 1,352	1,270	$ 389
United Kingdom
Segment Reporting Information [Line Items]
Property and Equipment, net	512	535
Australia
Segment Reporting Information [Line Items]
Property and Equipment, net	144	191	58
Other Europe
Segment Reporting Information [Line Items]
Property and Equipment, net	$ 553
Other International
Segment Reporting Information [Line Items]
Property and Equipment, net		$ 902	$ 87