Stock-Based Compensation Schedule of Share Repurchases (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	May 08, 2017	May 04, 2015
May 2015 Repurchase Program [Member] [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 0	$ 127	$ 31	$ 256
Stock Repurchase Program, Authorized Amount						$ 1,000
Stock Repurchased and Retired During Period, Shares	0.0	1.6	0.3	3.5
May 2017 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 153		$ 272
Stock Repurchase Program, Authorized Amount					$ 1,200
Stock Repurchased and Retired During Period, Shares	1.3		2.4
Repurchase Program, Total
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 153	$ 127	$ 303	$ 256
Stock Repurchased and Retired During Period, Shares	1.3	1.6	2.7	3.5