| **Accumulated Other Comprehensive Income (Tables)**                                      | 9 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 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) |
| 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 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.
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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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