| **Accumulated Other Comprehensive Income (Tables)**                                      | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
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| **Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]**                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
| Components of Accumulated Other Comprehensive Income (Loss) [Table Text Block]           | The changes in accumulated other comprehensive income (loss) by component, net of tax, for the three months ended September 30, 2016 and 2015 are as follows (in millions): Unrealized Net Gains (Losses) on Available-for-Sale Securities Unrealized Net Gains (Losses) on Derivative Instruments Foreign Currency Translation Adjustments TotalBalances as of June 30, 2016$3 $36 $(36) $3Other comprehensive income (loss) before reclassifications(1) (1) (6) (8)Amounts reclassified from accumulated other comprehensive income (loss)(1) (4) — (5)Total other comprehensive income (loss), net of tax(2) (5) (6) (13)Balance as of September 30, 2016$1 $31 $(42) $(10) Unrealized Net Gains (Losses) on Available-for-Sale Securities Unrealized Net Gains (Losses) on Derivative Instruments Foreign Currency Translation Adjustments TotalBalances as of June 30, 2015$(4) $5 $(15) $(14)Other comprehensive income (loss) before reclassifications2 5 (32) (25)Amounts reclassified from accumulated other comprehensive income (loss)(1) (4) — (5)Total other comprehensive income (loss), net of tax1 1 (32) (30)Balance as of September 30, 2015$(3) $6 $(47) $(44)The changes in accumulated other comprehensive income (loss) by component, net of tax, for the six months ended September 30, 2016 and 2015 are as follows (in millions): Unrealized Net Gains (Losses) on Available-for-Sale Securities Unrealized Net Gains (Losses) on Derivative Instruments Foreign Currency Translation Adjustments TotalBalances as of March 31, 2016$1 $14 $(31) $(16)Other comprehensive income (loss) before reclassifications1 27 (11) 17Amounts reclassified from accumulated other comprehensive income (loss)(1) (10) — (11)Total other comprehensive income (loss), net of tax— 17 (11) 6Balance as of September 30, 2016$1 $31 $(42) $(10) Unrealized Net Gains (Losses) on Available-for-Sale Securities Unrealized Net Gains (Losses) on Derivative Instruments Foreign Currency Translation Adjustments TotalBalances as of March 31, 2015$(3) $21 $(16) $2Other comprehensive income (loss) before reclassifications1 (8) (31) (38)Amounts reclassified from accumulated other comprehensive income (loss)(1) (7) — (8)Total other comprehensive income (loss), net of tax— (15) (31) (46)Balance as of September 30, 2015$(3) $6 $(47) $(44) |
| Reclassification out of Accumulated Other Comprehensive Income (Loss) [Table Text Block] | The effects on net income of amounts reclassified from accumulated other comprehensive income (loss) for the three and six months ended September 30, 2016 were as follows (in millions): Amount Reclassified From Accumulated Other Comprehensive Income (Loss)Statement of Operations ClassificationThree Months Ended September 30, 2016Six Months Ended September 30, 2016(Gains) losses on available-for-sale securitiesInterest and other income (expense), net $(1) $(1)Net of tax$(1)$(1)(Gains) losses on cash flow hedges from forward contracts    Net revenue$(4)$(9)Research and development—(1)Net of tax $(4) $(10)     Total (gain) loss reclassified, net of tax$(5)$(11)The effects on net income of amounts reclassified from accumulated other comprehensive income (loss) for the three and six months ended September 30, 2015 were as follows (in millions):  Amount Reclassified From Accumulated Other Comprehensive Income (Loss)Statement of Operations Classification Three Months Ended September 30, 2015 Six Months Ended September 30, 2015(Gains) losses on available-for-sale securities    Interest and other income (expense), net $(1) $(1)Net of tax $(1) $(1)     (Gains) losses on cash flow hedges from forward contracts    Net revenue $(6) $(14)Research and development 2 7Net of tax $(4) $(7)     Total (gain) loss reclassified, net of tax $(5) $(8)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |

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| - References
No definition available.
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| - Definition
Tabular disclosure of information about items reclassified out of accumulated other comprehensive income (loss).
+ References
No definition available.
+ Details**Name:**us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTableTextBlock**Namespace Prefix:**us-gaap_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |
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| - Definition
Tabular disclosure of the components of accumulated other comprehensive income (loss).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669686-108580
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