Description Of Business And Basis Of Presentation New revenue standard adoption - Income Statement at Period End (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Income Statements, Captions [Line Items]
Net revenue	$ 1,286	$ 959	$ 2,423	$ 2,408
Cost of Revenue	418	389	633	543
Gross Profit	868	570	1,790	1,865
Operating Expenses	610	611	1,232	1,163
Operating Income (Loss)	258	(41)	558	702
Interest and other income (expense), net	18	3	37	9
Income before provision for income taxes	276	(38)	595	711
Provision for income taxes	21	(16)	47	89
Net income (loss)	$ 255	$ (22)	$ 548	$ 622
Earnings Per Share, Basic	$ 0.84	$ (0.07)	$ 1.80	$ 2.01
Earnings Per Share, Diluted	$ 0.83	$ (0.07)	$ 1.77	$ 1.99
Difference between Revenue Guidance in Effect before and after Topic 606, Percentage [Member]
Condensed Income Statements, Captions [Line Items]
Revenues, percent	35.00%		2.00%
Cost of revenue, percent	12.00%		17.00%
Gross profit, percent	50.00%		(2.00%)
Operating expenses, percent	0.00%		0.00%
Operating income (loss), percent	(960.00%)		(7.00%)
Other nonoperating income (expense), percent	0.00%		0.00%
Income before provision for income taxes, percent	(2400.00%)		(6.00%)
Income tax expense (benefit), percent	200.00%		(34.00%)
Net income (loss), percent	(1442.00%)		(3.00%)
Earnings per share, basic, percent	(1500.00%)		(3.00%)
Earnings per share, diluted, percent	(1483.00%)		(3.00%)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Condensed Income Statements, Captions [Line Items]
Net revenue	$ 332		$ 53
Cost of Revenue	44		93
Gross Profit	288		(40)
Operating Expenses	0		0
Operating Income (Loss)	288		(40)
Interest and other income (expense), net	0		0
Income before provision for income taxes	288		(40)
Provision for income taxes	14		(24)
Net income (loss)	$ 274		$ (16)
Earnings Per Share, Basic	$ 0.90		$ (0.05)
Earnings Per Share, Diluted	$ 0.89		$ (0.06)
Product [Member]
Condensed Income Statements, Captions [Line Items]
Net revenue	$ 623	$ 454	$ 825	$ 1,282
Cost of Revenue	$ 222	300	$ 290	364
Product [Member] | Difference between Revenue Guidance in Effect before and after Topic 606, Percentage [Member]
Condensed Income Statements, Captions [Line Items]
Revenues, percent	43.00%		(28.00%)
Cost of revenue, percent	(21.00%)		(19.00%)
Product [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Condensed Income Statements, Captions [Line Items]
Net revenue	$ 186		$ (328)
Cost of Revenue	(58)		(68)
Service [Member]
Condensed Income Statements, Captions [Line Items]
Net revenue	663	505	1,598	1,126
Cost of Revenue	$ 196	$ 89	$ 343	$ 179
Service [Member] | Difference between Revenue Guidance in Effect before and after Topic 606, Percentage [Member]
Condensed Income Statements, Captions [Line Items]
Revenues, percent	28.00%		31.00%
Cost of revenue, percent	109.00%		88.00%
Service [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Condensed Income Statements, Captions [Line Items]
Net revenue	$ 146		$ 381
Cost of Revenue	102		161
Accounting Standards Update 2014-09 [Member]
Condensed Income Statements, Captions [Line Items]
Net revenue	1,286		2,423
Cost of Revenue	418		633
Gross Profit	868		1,790
Operating Expenses	610		1,232
Operating Income (Loss)	258		558
Interest and other income (expense), net	18		37
Income before provision for income taxes	276		595
Provision for income taxes	21		47
Net income (loss)	$ 255		$ 548
Earnings Per Share, Basic	$ 0.84		$ 1.80
Earnings Per Share, Diluted	$ 0.83		$ 1.77
Accounting Standards Update 2014-09 [Member] | Product [Member]
Condensed Income Statements, Captions [Line Items]
Net revenue	$ 623		$ 825
Cost of Revenue	222		290
Accounting Standards Update 2014-09 [Member] | Service [Member]
Condensed Income Statements, Captions [Line Items]
Net revenue	663		1,598
Cost of Revenue	196		343
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Condensed Income Statements, Captions [Line Items]
Net revenue	954		2,370
Cost of Revenue	374		540
Gross Profit	580		1,830
Operating Expenses	610		1,232
Operating Income (Loss)	(30)		598
Interest and other income (expense), net	18		37
Income before provision for income taxes	(12)		635
Provision for income taxes	7		71
Net income (loss)	$ (19)		$ 564
Earnings Per Share, Basic	$ (0.06)		$ 1.85
Earnings Per Share, Diluted	$ (0.06)		$ 1.83
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Product [Member]
Condensed Income Statements, Captions [Line Items]
Net revenue	$ 437		$ 1,153
Cost of Revenue	280		358
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Service [Member]
Condensed Income Statements, Captions [Line Items]
Net revenue	517		1,217
Cost of Revenue	$ 94		$ 182