| **Accumulated Other Comprehensive Income**                               | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
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| **Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
| Comprehensive Income (Loss)                                              | (5) ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)The changes in accumulated other comprehensive income (loss) by component, net of tax, for the three months ended December 31, 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 September 30, 2016$1 $31 $(42) $(10)Other comprehensive income (loss) before reclassifications(5) 39 (17) 17Amounts reclassified from accumulated other comprehensive income (loss)— (8) — (8)Total other comprehensive income (loss), net of tax(5) 31 (17) 9Balance as of December 31, 2016$(4) $62 $(59) $(1) Unrealized Net Gains (Losses) on Available-for-Sale Securities Unrealized Net Gains (Losses) on Derivative Instruments Foreign Currency Translation Adjustments TotalBalances as of September 30, 2015$(3) $6 $(47) $(44)Other comprehensive income (loss) before reclassifications(4) 10 (16) (10)Amounts reclassified from accumulated other comprehensive income (loss)1 (4) — (3)Total other comprehensive income (loss), net of tax(3) 6 (16) (13)Balance as of December 31, 2015$(6) $12 $(63) $(57)The changes in accumulated other comprehensive income (loss) by component, net of tax, for the nine months ended December 31, 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) $(16)Other comprehensive income (loss) before reclassifications(4) 66 (28) 34Amounts reclassified from accumulated other comprehensive income (loss)(1) (18) — (19)Total other comprehensive income (loss), net of tax(5) 48 (28) 15Balance as of December 31, 2016$(4) $62 $(59) $(1) Unrealized Net Gains (Losses) on Available-for-Sale Securities Unrealized Net Gains (Losses) on Derivative Instruments Foreign Currency Translation Adjustments TotalBalances as of March 31, 2015$(3) $21 $(16) $2Other comprehensive income (loss) before reclassifications(3) 2 (47) (48)Amounts reclassified from accumulated other comprehensive income (loss)— (11) — (11)Total other comprehensive income (loss), net of tax(3) (9) (47) (59)Balance as of December 31, 2015$(6) $12 $(63) $(57)The effects on net income of amounts reclassified from accumulated other comprehensive income (loss) for the three and nine months ended December 31, 2016 were as follows (in millions): Amount Reclassified From Accumulated Other Comprehensive Income (Loss)Statement of Operations ClassificationThree Months Ended December 31, 2016Nine Months Ended December 31, 2016(Gains) losses on available-for-sale securitiesInterest and other income (expense), net $— $(1)Net of tax$—$(1)(Gains) losses on cash flow hedges from forward contracts    Net revenue$(9)$(18)Research and development1—Net of tax $(8) $(18)     Total net (gain) loss reclassified, net of tax$(8)$(19)The effects on net income of amounts reclassified from accumulated other comprehensive income (loss) for the three and nine months ended December 31, 2015 were as follows (in millions):  Amount Reclassified From Accumulated Other Comprehensive Income (Loss)Statement of Operations Classification Three Months Ended December 31, 2015 Nine Months Ended December 31, 2015(Gains) losses on available-for-sale securities    Interest and other income (expense), net $1 $—Net of tax $1 $—     (Gains) losses on cash flow hedges from forward contracts    Net revenue $(5) $(19)Research and development 1 8Net of tax $(4) $(11)     Total net (gain) loss reclassified, net of tax $(3) $(11) |

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| - References
No definition available.
+ Details**Name:**us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
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| - Definition
Tabular disclosure of condensed statement of comprehensive income (loss) including, but not limited to, statements of comprehensive income (loss) of consolidated entities and consolidation eliminations.
+ References
No definition available.
+ Details**Name:**us-gaap_CondensedStatementOfComprehensiveIncomeTableTextBlock**Namespace Prefix:**us-gaap_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |