| **Income Taxes (Tables)**                                                 | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
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| **Income Tax Disclosure [Abstract]**                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| Components Of Income Before Provision For (Benefit From) Income Taxes     | The components of our income before provision for (benefit from) income taxes for the fiscal years ended March 31, 2016, 2015 and 2014 are as follows (in millions):  Year Ended March 31, 2016 2015 2014Domestic$133 $232 $(146)Foreign744 693 153Income before provision for (benefit from) income taxes$877 $925 $7                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| Provision For (Benefit From) Income Taxes                                 | Provision for (benefit from) income taxes for the fiscal years ended March 31, 2016, 2015 and 2014 consisted of (in millions): Current Deferred TotalYear Ended March 31, 2016     Federal$69 $(376) $(307)State5 (14) (9)Foreign36 1 37 $110 $(389) $(279)Year Ended March 31, 2015     Federal$10 $17 $27State— — —Foreign21 2 23 $31 $19 $50Year Ended March 31, 2014     Federal$(2) $(9) $(11)State1 (2) (1)Foreign8 3 11 $7 $(8) $(1)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| Schedule Of Differences Between Statutory Tax Rate And Effective Tax Rate | The differences between the statutory tax expense rate and our effective tax expense (benefit) rate, expressed as a percentage of income before provision for (benefit from) income taxes, for the fiscal years ended March 31, 2016, 2015 and 2014 were as follows:  Year Ended March 31, 2016 2015 2014Statutory federal tax expense rate35.0 % 35.0 % 35.0 %State taxes, net of federal benefit0.5 % 0.1 % (242.9)%Differences between statutory rate and foreign effective tax rate(22.1)% (22.3)% (142.9)%Valuation allowance(51.7)% (9.2)% 936.5 %Research and development credits(0.6)% (1.1)% (128.6)%Unremitted earnings of foreign subsidiaries4.9 % — — %Resolution of tax matters with authorities— % (0.5)% (657.1)%Non-deductible stock-based compensation3.1 % 3.5 % 385.7 %Acquisition-related contingent consideration— % (0.2)% (185.7)%Other(0.9)% 0.1 % (14.3)%Effective tax expense (benefit) rate(31.8)% 5.4 % (14.3)%                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| Deferred Tax Assets And Liabilities                                       | The components of net deferred tax assets, as of March 31, 2016 and 2015 consisted of (in millions):  As of March 31, 2016 2015Deferred tax assets:   Accruals, reserves and other expenses$171 $189Tax credit carryforwards334 312Stock-based compensation39 35Net operating loss & capital loss carryforwards28 41Total572 577Valuation allowance(114) (555)Deferred tax assets, net of valuation allowance458 22Deferred tax liabilities:   Amortization and Depreciation(27) (32)Unremitted earnings of foreign subsidiaries(43) —Prepaids and other liabilities(3) (8)Total(73) (40)Deferred tax assets, net of valuation allowance and deferred tax liabilities$385 $(18)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
| Schedule Of Unrecognized Tax Benefits                                     | A reconciliation of the beginning and ending balance of unrecognized tax benefits is summarized as follows (in millions): Balance as of March 31, 2013$297Increases in unrecognized tax benefits related to prior year tax positions10Decreases in unrecognized tax benefits related to prior year tax positions(79)Increases in unrecognized tax benefits related to current year tax positions44Decreases in unrecognized tax benefits related to settlements with taxing authorities(29)Reductions in unrecognized tax benefits due to lapse of applicable statute of limitations(9)Changes in unrecognized tax benefits due to foreign currency translation(2)Balance as of March 31, 2014232Increases in unrecognized tax benefits related to prior year tax positions9Decreases in unrecognized tax benefits related to prior year tax positions(14)Increases in unrecognized tax benefits related to current year tax positions50Decreases in unrecognized tax benefits related to settlements with taxing authorities(6)Reductions in unrecognized tax benefits due to lapse of applicable statute of limitations(7)Changes in unrecognized tax benefits due to foreign currency translation(10)Balance as of March 31, 2015254Increases in unrecognized tax benefits related to prior year tax positions33Decreases in unrecognized tax benefits related to prior year tax positions(4)Increases in unrecognized tax benefits related to current year tax positions63Decreases in unrecognized tax benefits related to settlements with taxing authorities(10)Reductions in unrecognized tax benefits due to lapse of applicable statute of limitations(4)Changes in unrecognized tax benefits due to foreign currency translation(1)Balance as of March 31, 2016$331 |

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No definition available.
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| - Definition
Tabular disclosure of the components of income tax expense attributable to continuing operations for each year presented including, but not limited to: current tax expense (benefit), deferred tax expense (benefit), investment tax credits, government grants, the benefits of operating loss carryforwards, tax expense that results from allocating certain tax benefits either directly to contributed capital or to reduce goodwill or other noncurrent intangible assets of an acquired entity, adjustments of a deferred tax liability or asset for enacted changes in tax laws or rates or a change in the tax status of the entity, and adjustments of the beginning-of-the-year balances of a valuation allowance because of a change in circumstances that causes a change in judgment about the realizability of the related deferred tax asset in future years.
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| - Definition
Tabular disclosure of the components of net deferred tax asset or liability recognized in an entity's statement of financial position, including the following: the total of all deferred tax liabilities, the total of all deferred tax assets, the total valuation allowance recognized for deferred tax assets.
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| - Definition
Tabular disclosure of the reconciliation using percentage or dollar amounts of the reported amount of income tax expense attributable to continuing operations for the year to the amount of income tax expense that would result from applying domestic federal statutory tax rates to pretax income from continuing operations.
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| - Definition
Tabular disclosure of income before income tax between domestic and foreign jurisdictions.
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| - Definition
Tabular disclosure of tax positions taken in the tax returns filed or to be filed for which it is more likely than not that the tax position will not be sustained upon examination by taxing authorities (i.e., uncertain tax positions) and other types of income tax contingencies, including: (1) the policy on classification of interest and penalties; (2) a tabular reconciliation of the total amounts of unrecognized tax benefits at the beginning and end of the period; the total amount(s) of: (3) unrecognized tax benefits that, if recognized, would affect the effective tax rate, and (4) interest and penalties recognized in each of the income statement and balance sheet; (5) for positions for which it is reasonably possible that the total amounts unrecognized will significantly change within 12 months of the reporting date the: (i) nature of the uncertainty, (ii) nature of the event that could occur that would cause the change, and (iii) an estimate of the range of the reasonably possible change or a statement that an estimate of the range cannot be made; and (6) a description of tax years that remain subject to examination by major tax jurisdictions.
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