Stock-Based Compensation And Employee Benefit Plans (Schedule of Share Repurchases) (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended			35 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	May 08, 2017	Feb. 17, 2016	May 04, 2015	May 05, 2014
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 601	$ 508	$ 1,018
Repurchase program, total
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 601	$ 508	$ 1,018
Stock repurchased and retired during period, Shares	5.3	6.5	15.7
May 2014 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount								$ 750
Stock Repurchased and Retired During Period, Value	$ 0	$ 0	$ 57	$ 394
Stock repurchased and retired during period, Shares	0.0	0.0	1.0	9.2
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	$ 31	$ 508	$ 461
Stock repurchased and retired during period, Shares	0.3	6.5	6.9
February 2016 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount						$ 500
Stock Repurchased and Retired During Period, Value	$ 0	$ 0	$ 500
Stock repurchased and retired during period, Shares	0.0	0.0	7.8
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	$ 570
Stock repurchased and retired during period, Shares	5.0
May 2018 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount					$ 2,400