Stock-Based Compensation Schedule of Share Repurchases (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 305	$ 300
May 2017 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 0	$ 76
Stock Repurchased and Retired During Period, Shares	0.0	0.6
May 2018 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 305	$ 224
Stock Repurchased and Retired During Period, Shares	3.2	1.7
Repurchase Program, Total
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 305	$ 300
Stock Repurchased and Retired During Period, Shares	3.2	2.3