Business Combinations - Acquisition of CoverMyMeds (Details) - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Apr. 03, 2017	May 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Business Acquisition [Line Items]
Purchase consideration paid in cash, net of cash acquired			$ 905	$ 2,893	$ 4,212
CMM
Business Acquisition [Line Items]
Purchase consideration paid in cash, net of cash acquired	$ 1,300
Additional contingent consideration that may be paid	160
Contingent consideration	$ 113		$ 69	$ 124
Cash payment for contingent consideration earned		$ 68