Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 4,502	$ 4,890
United States
Disaggregation of Revenue [Line Items]
Revenues	1,709	1,851
United Kingdom
Disaggregation of Revenue [Line Items]
Revenues	573	715
Australia
Disaggregation of Revenue [Line Items]
Revenues	361	373
Other Europe
Disaggregation of Revenue [Line Items]
Revenues	1,205	1,230
Other International
Disaggregation of Revenue [Line Items]
Revenues	$ 654	$ 721