Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 5,021	$ 5,178	$ 14,762	$ 15,473
United States
Disaggregation of Revenue [Line Items]
Revenues	1,843	1,917	5,500	5,667
United Kingdom
Disaggregation of Revenue [Line Items]
Revenues	707	749	2,100	2,309
Australia
Disaggregation of Revenue [Line Items]
Revenues	380	377	1,119	1,222
Other Europe
Disaggregation of Revenue [Line Items]
Revenues	1,329	1,384	3,819	3,994
Other International
Disaggregation of Revenue [Line Items]
Revenues	$ 762	$ 751	$ 2,224	$ 2,281