Stock-Based Compensation And Employee Benefit Plans (Schedule of Share Repurchases) (Details) - USD ($) shares in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	May 11, 2018	May 08, 2017	May 04, 2015
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 1,207,000,000	$ 1,192,000,000	$ 601,000,000
May 2015 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount						$ 1,000,000,000
Stock Repurchased and Retired During Period, Value	$ 0	$ 0	$ 31,000,000
Stock repurchased and retired during period, Shares	0.0	0.0	0.3
May 2017 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount					$ 1,200,000,000
Stock Repurchased and Retired During Period, Value	$ 0	$ 76,000,000	$ 570,000,000
Stock repurchased and retired during period, Shares	0.0	0.6	5.0
May 2018 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount				$ 2,400,000,000
Stock Repurchased and Retired During Period, Value	$ 1,207,000,000	$ 1,116,000,000
Stock repurchased and retired during period, Shares	12.3	10.4
Repurchase program, total
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 1,207,000,000	$ 1,192,000,000	$ 601,000,000
Stock repurchased and retired during period, Shares	12.3	11.0	5.3