v2.4.0.6

Earnings per Share (Tables) | 9 Months Ended
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Sep. 30, 2012
Earnings Per Share [Abstract] |
Basic and diluted earnings per share |
| For the Three Months Ended September 30, |  | For the Nine Months Ended September 30,
(In millions) | 2012 |  | 2011 |  | 2012 |  | 2011
Numerator: |  |  |  |  |  |  |
Net income attributable to Biogen Idec Inc. | $ | 398.4 |  |  | $ | 351.8 |  |  | $ | 1,087.9 |  |  | $ | 934.2 |
Adjustment for net income allocable to preferred stock | — |  |  | — |  |  | — |  |  | (0.6 | )
Net income used in calculating basic and diluted earnings per share | $ | 398.4 |  |  | $ | 351.8 |  |  | $ | 1,087.9 |  |  | $ | 933.6 |
Denominator: |  |  |  |  |  |  |
Weighted average number of common shares outstanding | 236.5 |  |  | 242.9 |  |  | 238.3 |  |  | 242.3 |
Effect of dilutive securities: |  |  |  |  |  |  |
Stock options and employee stock purchase plan | 0.4 |  |  | 0.7 |  |  | 0.5 |  |  | 1.1 |
Time-vested restricted stock units | 0.9 |  |  | 1.6 |  |  | 1.0 |  |  | 1.5 |
Market stock units | 0.3 |  |  | 0.2 |  |  | 0.3 |  |  | 0.2 |
Dilutive potential common shares | 1.6 |  |  | 2.5 |  |  | 1.8 |  |  | 2.8 |
Shares used in calculating diluted earnings per share | 238.1 |  |  | 245.4 |  |  | 240.1 |  |  | 245.1 |

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- Definition Tabular disclosure of an entity's basic and diluted earnings per share calculations. + References No definition available. + Details
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