| **Goodwill And Acquisition-Related Intangibles, Net**    | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
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| **Goodwill and Intangible Assets Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| Goodwill And Acquisition-Related Intangibles, Net        | (6) GOODWILL AND ACQUISITION-RELATED INTANGIBLES, NETThe changes in the carrying amount of goodwill for the nine months ended December 31, 2016 are as follows (in millions): As of March 31, 2016 Activity Effects of Foreign Currency Translation As of December 31, 2016Goodwill$2,078 $— $(6) $2,072Accumulated impairment(368) — — (368)Total$1,710 $— $(6) $1,704Goodwill represents the excess of the purchase price over the fair value of the underlying acquired net tangible and intangible assets. Goodwill is not amortized, but rather subject to at least an annual assessment for impairment by applying a fair value-based test. Acquisition-related intangibles consisted of the following (in millions): As of December 31, 2016 As of March 31, 2016 GrossCarryingAmount AccumulatedAmortization Acquisition-RelatedIntangibles, Net GrossCarryingAmount AccumulatedAmortization Acquisition-RelatedIntangibles, NetDeveloped and core technology$412 $(412) $— $412 $(368) $44Trade names and trademarks106 (97) 9 106 (93) 13Registered user base and other intangibles5 (5) — 5 (5) —Carrier contracts and related85 (85) — 85 (85) —Total$608 $(599) $9 $608 $(551) $57Amortization of intangibles for the three and nine months ended December 31, 2016 and 2015 are classified in the Condensed Consolidated Statement of Operations as follows (in millions): Three Months Ended December 31, Nine Months Ended December 31, 2016 2015 2016 2015Cost of service and other$— $9 $16 $25Cost of product18 3 27 10Operating expenses2 2 5 6Total$20 $14 $48 $41During the three and nine months ended December 31, 2016, we determined that the carrying value of one of our acquisition-related intangible assets was not recoverable. The acquisition-related intangible asset was measured using Level 3 inputs and was written down to a fair value of zero as of December 31, 2016. We recognized an impairment charge of $15 million in cost of product revenue in our Condensed Consolidated Statements of Operations. During the three and nine months ended December 31, 2015, there were no impairment charges for acquisition-related intangible assets.Acquisition-related intangible assets are amortized using the straight-line method over the lesser of their estimated useful lives or the agreement terms, typically from 2 to 14 years. As of December 31, 2016 and March 31, 2016, the weighted-average remaining useful life for acquisition-related intangible assets was approximately 1.6 years and 1.6 years, respectively. As of December 31, 2016, future amortization of acquisition-related intangibles that will be recorded in the Condensed Consolidated Statement of Operations is estimated as follows (in millions): Fiscal Year Ending March 31, 2017 (remaining three months)$12018620192Total$9 |

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No definition available.
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| - Definition
The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final.  May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.
+ References
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