Segment and Geographic Information - Geographic PPE (Details) - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Total Property and Equipment, net	$ 2,946	$ 3,547
United States
Segment Reporting Information [Line Items]
Total Property and Equipment, net	1,189	1,621
U.K.
Segment Reporting Information [Line Items]
Total Property and Equipment, net	465	493
Australia
Segment Reporting Information [Line Items]
Total Property and Equipment, net	149	134
Other Europe
Segment Reporting Information [Line Items]
Total Property and Equipment, net	603	757
Other International
Segment Reporting Information [Line Items]
Total Property and Equipment, net	$ 540	$ 542