Stock-Based Compensation Schedule of Share Repurchases (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended			9 Months Ended
	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 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	$ 31	$ 127	$ 31	$ 383
Stock Repurchase Program, Authorized Amount							$ 1,000
Stock Repurchased and Retired During Period, Shares	0.0	0.3	1.5	0.3	5.0
May 2017 Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 150			$ 422
Stock Repurchase Program, Authorized Amount						$ 1,200
Stock Repurchased and Retired During Period, Shares	1.4			3.8
Repurchase Program, Total
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Value	$ 150		$ 127	$ 453	$ 383
Stock Repurchased and Retired During Period, Shares	1.4		1.5	4.1	5.0