| **Earnings (Loss) Per Share (Tables)**                                     | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
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| **Earnings Per Share Reconciliation [Abstract]**                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| Computation Of Basic Earnings (Loss) And Diluted Earnings (Loss) Per Share | The following table summarizes the computations of basic earnings per share (“Basic EPS”) and diluted earnings per share (“Diluted EPS”). Basic EPS is computed as net income divided by the weighted-average number of common shares outstanding for the period. Diluted EPS reflects the potential dilution that could occur from common shares issuable through stock-based compensation plans including stock options, restricted stock, restricted stock units, ESPP purchase rights, warrants, and other convertible securities using the treasury stock method. Three Months Ended September 30,    Six Months Ended September 30, (In millions, except per share amounts)2016 2015 2016 2015Net income (loss)$(38) $(140) $402 $302Shares used to compute earnings (loss) per share:       Weighted-average common stock outstanding — basic301 312 301 311Dilutive potential common shares related to stock award plans and from assumed exercise of stock options— — 3 7Dilutive potential common shares related to the Convertible Notes— — 2 9Dilutive potential common shares related to the Warrants— — 9 7Weighted-average common stock outstanding — diluted301 312 315 334Earnings (loss) per share:       Basic$(0.13) $(0.45) $1.34 $0.97Diluted$(0.13) $(0.45) $1.28 $0.90 |

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| - References
No definition available.
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| - Definition
Tabular disclosure of an entity's basic and diluted earnings per share calculations, including a reconciliation of numerators and denominators of the basic and diluted per-share computations for income from continuing operations.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257
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