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Share-Based Payments (Tables) | 12 Months Ended
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Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |
Share-based compensation expense included in consolidated statements of income | The following table summarizes share-based compensation expense included in our consolidated statements of income:
| For the Years Ended December 31,
(In millions) | 2017 |  | 2016 |  | 2015
Research and development | $ | 74.0 |  |  | $ | 84.5 |  |  | $ | 88.6 |
Selling, general and administrative | 95.7 |  |  | 121.7 |  |  | 127.3 |
Restructuring charges | — |  |  | (1.8 | ) |  | (8.6 | )
Subtotal | 169.7 |  |  | 204.4 |  |  | 207.3 |
Capitalized share-based compensation costs | (9.6 | ) |  | (14.6 | ) |  | (11.0 | )
Share-based compensation expense included in total cost and expenses | 160.1 |  |  | 189.8 |  |  | 196.3 |
Income tax effect | (42.8 | ) |  | (54.0 | ) |  | (55.8 | )
Share-based compensation expense included in net income attributable to Biogen Inc. | $ | 117.3 |  |  | $ | 135.8 |  |  | $ | 140.5 |
Summary of share-based compensation expense associated with each of our share-based compensating programs | The following table summarizes share-based compensation expense associated with each of our share-based compensation programs:
| For the Years Ended December 31,
(In millions) | 2017 |  | 2016 |  | 2015
Market stock units | $ | 22.4 |  |  | $ | 38.4 |  |  | $ | 38.1 |
Time-vested restricted stock units | 107.3 |  |  | 120.0 |  |  | 119.0 |
Cash settled performance units | 18.4 |  |  | 16.3 |  |  | 22.4 |
Performance units | 12.3 |  |  | 18.6 |  |  | 13.9 |
Employee stock purchase plan | 9.3 |  |  | 11.1 |  |  | 13.9 |
Subtotal | 169.7 |  |  | 204.4 |  |  | 207.3 |
Capitalized share-based compensation costs | (9.6 | ) |  | (14.6 | ) |  | (11.0 | )
Share-based compensation expense included in total cost and expenses | $ | 160.1 |  |  | $ | 189.8 |  |  | $ | 196.3 |
Stock option activity | The following table summarizes our stock option activity:
| Shares |  | Weighted Average Exercise Price
Outstanding at December 31, 2016 | 66,000 |  |  | $ | 54.06 |
Hemophilia spin-off adjustment | — |  |  | $ | — |
Granted | — |  |  | $ | — |
Exercised | (14,000 | ) |  | $ | 50.89 |
Cancelled | (10,000 | ) |  | $ | 55.11 |
Outstanding at December 31, 2017 | 42,000 |  |  | $ | 53.83 |
Tax benefit and cash received from stock option exercises | The following table summarizes the amount of tax benefit realized for stock options and cash received from the exercise of stock options:
| For the Years Ended December 31,
(In millions) | 2017 |  | 2016 |  | 2015
Tax benefit realized for stock options | $ | 3.4 |  |  | $ | 4.0 |  |  | $ | 11.9 |
Cash received from the exercise of stock options | $ | 0.7 |  |  | $ | 2.2 |  |  | $ | 6.3 |
Market stock units activity | The following table summarizes our MSU activity:
| Shares |  | Weighted Average Grant Date Fair Value
Unvested at December 31, 2016 | 230,000 |  |  | $ | 355.60 |
Hemophilia spin-off adjustment | 4,000 |  |  | $ | — |
Granted (a) | 94,000 |  |  | $ | 382.59 |
Vested | (112,000 | ) |  | $ | 311.17 |
Forfeited | (45,000 | ) |  | $ | 372.35 |
Unvested at December 31, 2017 | 171,000 |  |  | $ | 370.83 |
Assumptions used in valuation of market based stock units | The assumptions used in our valuation are summarized as follows:
| For the Years Ended December 31,
| 2017 |  | 2016 |  | 2015
Expected dividend yield | —% |  | —% |  | —%
Range of expected stock price volatility | 33.0% - 35.6% |  | 38.2% - 40.7% |  | 31.0% - 33.2%
Range of risk-free interest rates | 0.9% - 1.6% |  | 0.6% - 0.9% |  | 0.2% - 1.0%
30 calendar day average stock price on grant date | $263.18 - $267.88 |  | $260.67 - $304.86 |  | $277.35 - $426.27
Weighted-average per share grant date fair value | $382.59 |  | $328.03 |  | $493.43
Cash settled performance shares activity | The following table summarizes our CSPU activity:
| Shares
Unvested at December 31, 2016 | 122,000 |
Hemophilia spin-off adjustment | 3,000 |
Granted (a) | 83,000 |
Vested | (69,000 | )
Forfeited | (34,000 | )
Unvested at December 31, 2017 | 105,000 |
Performance units activity | The following table summarizes our PU activity:
| Shares
Unvested at December 31, 2016 | 110,000 |
Hemophilia spin-off adjustment | 3,000 |
Granted (a) | 40,000 |
Vested | (43,000 | )
Forfeited | (19,000 | )
Unvested at December 31, 2017 | 91,000 |
Time-vested restricted stock units activity | The following table summarizes our RSU activity:
| Shares |  | Weighted Average Grant Date Fair Value
Unvested at December 31, 2016 | 888,000 |  |  | $ | 303.49 |
Hemophilia spin-off adjustment | 12,000 |  |  | $ | — |
Granted (a) | 464,000 |  |  | $ | 293.41 |
Vested | (350,000 | ) |  | $ | 308.04 |
Forfeited | (182,000 | ) |  | $ | 292.57 |
Unvested at December 31, 2017 | 832,000 |  |  | $ | 291.85 |
Shares issued under employee stock purchase plan | The following table summarizes our ESPP activity:
| For the Years Ended December 31,
(In millions, except share amounts) | 2017 |  | 2016 |  | 2015
Shares issued under the 2015 ESPP | 167,000 |  |  | 190,000 |  |  | 78,000 |
Shares issued under the 1995 ESPP | — |  |  | — |  |  | 98,000 |
Cash received under the 2015 ESPP | $ | 39.8 |  |  | $ | 41.5 |  |  | $ | 19.3 |
Cash received under the 1995 ESPP | $ | — |  |  | $ | — |  |  | $ | 30.0 |

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