|**Earnings Per Share (Tables)**                                                                          | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
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|**Earnings Per Share Reconciliation [Abstract]**                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Computation Of Basic Earnings And Diluted Earnings Per Share                                             | Year Ended March 31,(In millions, except per share amounts)201620152014Net income$1,156$875$8Shares used to compute earnings per share:Weighted-average common stock outstanding — basic310311308Dilutive potential common shares related to stock award plans and from assumed exercise of stock options698Dilutive potential common shares related to the Convertible Notes64—Dilutive potential common shares related to the Warrants81—Weighted-average common stock outstanding — diluted330325316Earnings per share:Basic$3.73$2.81$0.03Diluted$3.50$2.69$0.03
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|                                                                                                         | Year Ended March 31,                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|(In millions, except per share amounts)                                                                  | 2016                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Net income                                                                                               | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Shares used to compute earnings per share:                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted-average common stock outstanding — basic                                                        | 310                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Dilutive potential common shares related to stock award plans and from assumed exercise of stock options | 6                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Dilutive potential common shares related to the Convertible Notes                                        | 6                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Dilutive potential common shares related to the Warrants                                                 | 8                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Weighted-average common stock outstanding — diluted                                                      | 330                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Earnings per share:                                                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Basic                                                                                                    | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Diluted                                                                                                  | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   

X- ReferencesNo definition available.
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duration X- DefinitionTabular 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.
+ ReferencesReference 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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