Stock-Based Compensation (Schedule Of Stock-Based Compensation Expense By Statement Of Operations) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Excess Tax Benefit from Share-based Compensation, Financing Activities	$ 4	$ 25	$ 37	$ 65
Stock-based compensation expense	48	44	96	89
Cost of Sales [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	1	1	2	1
Research And Development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	27	25	54	51
Marketing and Sales [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	8	7	15	12
General And Administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	12	$ 11	25	$ 25
Stock-based compensation expense [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Deferred Income Tax Expense (Benefit)	$ 9		$ 18