| **Goodwill And Acquisition-Related Intangibles, Net (Schedule Of Acquisition-Related Intangibles) (Details) (USD $)In Millions, unless otherwise specified** | Dec. 31, 2013 | Mar. 31, 2013 |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Finite-Lived Intangible Assets**                                                                                                                           |          |          |  |
| Gross carrying amount                                                                                                                                        | $ 833         | $ 833         |  |
| Accumulated amortization                                                                                                                                     | (637)         | (580)         |  |
| Acquisition-related intangibles, net                                                                                                                         | 196           | 253           | [1] |
| Developed And Core Technology                                                                                                                                |          |          |  |
| **Finite-Lived Intangible Assets**                                                                                                                           |          |          |  |
| Gross carrying amount                                                                                                                                        | 531           | 527           |  |
| Accumulated amortization                                                                                                                                     | (370)         | (324)         |  |
| Acquisition-related intangibles, net                                                                                                                         | 161           | 203           |  |
| Trade Names And Trademarks                                                                                                                                   |          |          |  |
| **Finite-Lived Intangible Assets**                                                                                                                           |          |          |  |
| Gross carrying amount                                                                                                                                        | 130           | 130           |  |
| Accumulated amortization                                                                                                                                     | (104)         | (99)          |  |
| Acquisition-related intangibles, net                                                                                                                         | 26            | 31            |  |
| Registered User Base And Other Intangibles                                                                                                                   |          |          |  |
| **Finite-Lived Intangible Assets**                                                                                                                           |          |          |  |
| Gross carrying amount                                                                                                                                        | 87            | 87            |  |
| Accumulated amortization                                                                                                                                     | (86)          | (84)          |  |
| Acquisition-related intangibles, net                                                                                                                         | 1             | 3             |  |
| Carrier Contracts And Related                                                                                                                                |          |          |  |
| **Finite-Lived Intangible Assets**                                                                                                                           |          |          |  |
| Gross carrying amount                                                                                                                                        | 85            | 85            |  |
| Accumulated amortization                                                                                                                                     | (77)          | (73)          |  |
| Acquisition-related intangibles, net                                                                                                                         | 8             | 12            |  |
| In-Process Research And Development                                                                                                                          |          |          |  |
| **Finite-Lived Intangible Assets**                                                                                                                           |          |          |  |
| Gross carrying amount                                                                                                                                        | 0             | 4             |  |
| Accumulated amortization                                                                                                                                     | 0             | 0             |  |
| Acquisition-related intangibles, net                                                                                                                         | $ 0           | $ 4           |  |
|                                                                                                                                                              |
| [1]Derived from audited consolidated financial statements.                                                                                                   |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275
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| X                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275
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