Business Acquisitions and Divestitures - Acquisition of CoverMyMeds (Details) - USD ($)		12 Months Ended
	Apr. 03, 2017	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Business Acquisition [Line Items]
Purchase consideration paid in cash, net of cash acquired		$ 133,000,000	$ 905,000,000	$ 2,893,000,000
CMM
Business Acquisition [Line Items]
Purchase consideration paid in cash, net of cash acquired	$ 1,300,000,000
Additional contingent consideration that may be paid	160,000,000
Contingent consideration	$ 113,000,000	$ 0	69,000,000
Cash payment for contingent consideration earned			$ 69,000,000	$ 68,000,000