Stock-Based Compensation Schedule of Share Repurchases (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	May 11, 2018	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	$ 31
Stock Repurchase Program, Authorized Amount					$ 1,000
Stock Repurchased and Retired During Period, Shares	0.0	0.3
May 2017 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 76	$ 119
Stock Repurchase Program, Authorized Amount				$ 1,200
Stock Repurchased and Retired During Period, Shares	0.6	1.1
May 2018 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 224
Stock Repurchase Program, Authorized Amount			$ 2,400
Stock Repurchased and Retired During Period, Shares	1.7
Repurchase Program, Total
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 300	$ 150
Stock Repurchased and Retired During Period, Shares	2.3	1.4