Stock-Based Compensation And Employee Benefit Plans (Schedule of Share Repurchases) (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	May 11, 2018	May 08, 2017	May 04, 2015
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ (1,192)	$ 601	$ 508
Repurchase program, total
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 1,192	$ 601	$ 508
Stock repurchased and retired during period, Shares	11.0	5.3	6.5
May 2015 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount						$ 1,000
Stock Repurchased and Retired During Period, Value	$ 0	$ 31	$ 508
Stock repurchased and retired during period, Shares	0.0	0.3	6.5
May 2017 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount					$ 1,200
Stock Repurchased and Retired During Period, Value	$ 76	$ 570
Stock repurchased and retired during period, Shares	0.6	5.0
May 2018 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount				$ 2,400
Stock Repurchased and Retired During Period, Value	$ 1,116
Stock repurchased and retired during period, Shares	10.4