Stockholders' Equity - Schedule of Share Repurchases (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	May 31, 2018
Stockholders' Equity Note [Abstract]
Total Number of Shares Purchased (in shares)		13.9	13.5	10.5
Average price paid per share (in dollars per share)	$ 143.66	$ 138.94	$ 130.72	$ 151.06
Approximate Dollar Value of Shares that May Yet Be Purchased Under the Programs
Beginning balance	$ 1,096	$ 3,469	$ 1,096	$ 2,746
Additional authorized					$ 4,000
Shares repurchased		(1,934)	(1,627)	(1,650)
Ending balance		$ 1,535	$ 3,469	$ 1,096