| Cover | 12 Months Ended |
| Dec. 31, 2022 | |
| Document Information [Line Items] | |
| Document Type | DEF 14A |
| Amendment Flag | false |
| Entity Information [Line Items] | |
| Entity Registrant Name | BIOGEN INC. |
| Entity Central Index Key | 0000875045 |
| Pay vs Performance Disclosure - USD ($) | 12 Months Ended | ||
| Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | |
| Pay vs Performance Disclosure [Table] | |||
| Pay vs Performance [Table Text Block] | As discussed in our CD&A above, our CMDC has implemented executive compensation programs designed to link a substantial part of our NEOs compensation to financial, strategic, and market-based measures and align realizable compensation with stockholder return. The following table sets forth additional compensation information for our NEOs, calculated in accordance with SEC regulations, for fiscal years 2022, 2021 and 2020. Pay versus Performance Tabular Disclosure: The table below contains information about the relationship between compensation actually paid, as computed in accordance with SEC rules, to our CEO and non-CEO hypothetical $100 investment in our common stock on December 31, 2019, and shows the value of that investment over time for each calendar year. A hypothetical $100 investment in the NASDAQ Biotech Index using the same methodology is shown for comparison. The CMDC did not consider the pay versus performance disclosure below in making its pay decisions for any of the fiscal years shown. In addition, the average non-CEO non-CEO Fiscal SCT Total for (1) SCT Total for (1) Compensation (2) Compensation (2) Average SCT Average (2)(3) Value of $100 Value of (4) Net Income Company (5) 2022 $ 30,488,593 $ 26,625,221 $ 27,551,849 $ 5,898,711 $ 5,878,461 $ 4,969,471 $ 93.32 $ 111.27 $ 3,047 $ 10,326M 2021 — $ 17,689,665 — $ 15,211,025 $ 5,761,560 $ 5,081,941 $ 80.85 $ 124.89 $ 1,556 $ 11,054M 2020 — $ 18,659,829 — $ 8,578,367 $ 6,525,375 $ 4,363,675 $ 82.52 $ 125.69 $ 4,001 $ 13,952M Notes to Pay Vs. Performance Table (1) The dollar amounts reported are the amounts of total compensation reported for our CEO, Mr. Viehbacher, and our former CEO, Mr. Vounatsos in the Summary Compensation Table for fiscal years 2022, 2021 and 2020. Mr. Vounatsos served as CEO for each of the full fiscal years 2021 and 2020, while Mr. Viehbacher and Mr. Vounatsos both served as CEO in fiscal year 2022. (2) The dollar amounts reported represent the amount of “compensation actually paid”, as computed in accordance with SEC rules. The dollar amounts do not reflect the actual amounts of compensation paid to our CEO and other NEOs during the applicable year, but also include (i) the year-end (3) For 2022, reflects compensation information for our NEOs, other than our CEO, as described in the CD&A of this proxy statement. For 2021, reflects compensation information for Mr. McDonnell, Ms. Alexander, Mr. Guindo and Alfred Sandrock, our former EVP of R&D. For 2020, reflects compensation information for Mr. McDonnell, Ms. Alexander, Mr. Guindo, Dr. Sandrock and Jeffrey Capello, our former CFO. (4) Reflects cumulative total stockholder return of the NASDAQ Biotechnology Index (NBI) as of December 31, 2022. The NBI is the peer group used by BIIB for the purposes of item 201(e) of Regulation S-K 10-K (5) Revenue was adjusted to neutralize the effects of foreign exchange rate fluctuations. The following tables set forth the adjustments made during each year in the PVP table to arrive at “compensation actually paid” to our Principal Executive Officer during each year. Fiscal Year Summary Summary Reported (1) Reported (1) Equity Award (2) Equity Award (2) Compensation Compensation 2022 $ 30,488,593 $ 26,625,221 $ 30,000,655 $ 15,389,732 $ 27,063,911 -$ 5,336,778 $ 27,551,849 $ 5,898,711 2021 — $ 17,689,665 — $ 14,084,314 — $ 11,605,674 — $ 15,211,025 2020 — $ 18,659,829 — $ 13,887,064 — $ 3,805,602 — $ 8,578,367 (1) Represents the grant date fair value of equity awards to our CEO and former CEO, as reported in the “Stock Awards” and “Option Awards” columns in the Summary Compensation Table for each applicable year. (2) Represents the year-over-year change in the fair value of equity awards to our CEO and former CEO, as itemized in the table below. No awards vested in the year they were granted. 2022 Fair Value of Equity Awards for CEO and former CEO Mr. Viehbacher Mr. Vounatsos 2021 2020 As of year-end $ 27,063,911 $ 1,996,870 $ 10,985,776 $ 8,893,002 Year-over-year increase or decrease of unvested awards granted in prior years $ 0 -$ 6,247,880 -$ 687,744 -$ 3,618,885 Increase or decrease from prior fiscal year-end $ 0 -$ 1,085,768 $ 1,307,643 -$ 1,468,515 Total Equity Award Adjustments $ 27,063,911 -$ 5,336,778 $ 11,605,674 $ 3,805,602 The following tables set forth the adjustments made during each year in the PVP table to arrive at “compensation actually paid” to our non-CEO Fiscal Year Average Summary Non-CEO Average Reported Awards for non-CEO (1) Average Equity for non-CEO NEOs (2) Average non-CEO NEOs 2022 $ 5,878,461 $ 4,223,226 $ 3,314,236 $ 4,969,471 2021 $ 5,761,560 $ 4,105,942 $ 3,426,323 $ 5,081,941 2020 $ 6,525,375 $ 4,158,006 $ 1,996,306 $ 4,363,675 (1) Represents the average of the grant date fair value of the equity awards to our named executive officers (other than our CEO and former CEO), as reported in the “Stock Awards” column in the SCT for each applicable year. (2) Represents the average of the year-over-year change in fair value of equity awards to our named executive officers (other than our CEO and former CEO), as itemized in the table below. No awards vested in the year they were granted. Average Fair Value of Equity Awards for non-CEO 2022 2021 2020 As of year-end $ 3,809,706 $ 3,295,987 $ 2,904,843 Year-over-year increase or decrease of unvested awards granted in prior years -$ 244,173 -$ 156,359 -$ 741,018 Increase or decrease from prior fiscal year-end -$ 251,296 $ 286,695 -$ 167,520 Total Equity Award Adjustments $ 3,314,236 $ 3,426,323 $ 1,996,306 | ||
| Company Selected Measure Name | Revenue | ||
| Named Executive Officers, Footnote [Text Block] | For 2022, reflects compensation information for our NEOs, other than our CEO, as described in the CD&A of this proxy statement. For 2021, reflects compensation information for Mr. McDonnell, Ms. Alexander, Mr. Guindo and Alfred Sandrock, our former EVP of R&D. For 2020, reflects compensation information for Mr. McDonnell, Ms. Alexander, Mr. Guindo, Dr. Sandrock and Jeffrey Capello, our former CFO | ||
| Peer Group Issuers, Footnote [Text Block] | Reflects cumulative total stockholder return of the NASDAQ Biotechnology Index (NBI) as of December 31, 2022. The NBI is the peer group used by BIIB for the purposes of item 201(e) of Regulation S-K 10-K | ||
| Adjustment To PEO Compensation, Footnote [Text Block] | The following tables set forth the adjustments made during each year in the PVP table to arrive at “compensation actually paid” to our Principal Executive Officer during each year. Fiscal Year Summary Summary Reported (1) Reported (1) Equity Award (2) Equity Award (2) Compensation Compensation 2022 $ 30,488,593 $ 26,625,221 $ 30,000,655 $ 15,389,732 $ 27,063,911 -$ 5,336,778 $ 27,551,849 $ 5,898,711 2021 — $ 17,689,665 — $ 14,084,314 — $ 11,605,674 — $ 15,211,025 2020 — $ 18,659,829 — $ 13,887,064 — $ 3,805,602 — $ 8,578,367 (1) Represents the grant date fair value of equity awards to our CEO and former CEO, as reported in the “Stock Awards” and “Option Awards” columns in the Summary Compensation Table for each applicable year. (2) Represents the year-over-year change in the fair value of equity awards to our CEO and former CEO, as itemized in the table below. No awards vested in the year they were granted. 2022 Fair Value of Equity Awards for CEO and former CEO Mr. Viehbacher Mr. Vounatsos 2021 2020 As of year-end $ 27,063,911 $ 1,996,870 $ 10,985,776 $ 8,893,002 Year-over-year increase or decrease of unvested awards granted in prior years $ 0 -$ 6,247,880 -$ 687,744 -$ 3,618,885 Increase or decrease from prior fiscal year-end $ 0 -$ 1,085,768 $ 1,307,643 -$ 1,468,515 Total Equity Award Adjustments $ 27,063,911 -$ 5,336,778 $ 11,605,674 $ 3,805,602 | ||
| Non-PEO NEO Average Total Compensation Amount | $ 5,878,461 | $ 5,761,560 | $ 6,525,375 |
| Non-PEO NEO Average Compensation Actually Paid Amount | $ 4,969,471 | 5,081,941 | 4,363,675 |
| Adjustment to Non-PEO NEO Compensation Footnote [Text Block] | The following tables set forth the adjustments made during each year in the PVP table to arrive at “compensation actually paid” to our non-CEO Fiscal Year Average Summary Non-CEO Average Reported Awards for non-CEO (1) Average Equity for non-CEO NEOs (2) Average non-CEO NEOs 2022 $ 5,878,461 $ 4,223,226 $ 3,314,236 $ 4,969,471 2021 $ 5,761,560 $ 4,105,942 $ 3,426,323 $ 5,081,941 2020 $ 6,525,375 $ 4,158,006 $ 1,996,306 $ 4,363,675 (1) Represents the average of the grant date fair value of the equity awards to our named executive officers (other than our CEO and former CEO), as reported in the “Stock Awards” column in the SCT for each applicable year. (2) Represents the average of the year-over-year change in fair value of equity awards to our named executive officers (other than our CEO and former CEO), as itemized in the table below. No awards vested in the year they were granted. Average Fair Value of Equity Awards for non-CEO 2022 2021 2020 As of year-end $ 3,809,706 $ 3,295,987 $ 2,904,843 Year-over-year increase or decrease of unvested awards granted in prior years -$ 244,173 -$ 156,359 -$ 741,018 Increase or decrease from prior fiscal year-end -$ 251,296 $ 286,695 -$ 167,520 Total Equity Award Adjustments $ 3,314,236 $ 3,426,323 $ 1,996,306 | ||
| Compensation Actually Paid vs. Total Shareholder Return [Text Block] | |||
| Compensation Actually Paid vs. Company Selected Measure [Text Block] | |||
| Total Shareholder Return Vs Peer Group [Text Block] | |||
| Tabular List [Table Text Block] | Most Important Performance Measures Revenue Total Shareholder Return Non-GAAP Pipeline Milestones | ||
| Total Shareholder Return Amount | $ 93.32 | 80.85 | 82.52 |
| Peer Group Total Shareholder Return Amount | 111.27 | 124.89 | 125.69 |
| Net Income (Loss) | $ 3,047,000,000 | $ 1,556,000,000 | $ 4,001,000,000 |
| Company Selected Measure Amount | 10,326,000,000 | 11,054,000,000 | 13,952,000,000 |
| Measure [Axis]: 1 | |||
| Pay vs Performance Disclosure [Table] | |||
| Measure Name | Revenue | ||
| Measure [Axis]: 2 | |||
| Pay vs Performance Disclosure [Table] | |||
| Measure Name | Total Shareholder Return | ||
| Measure [Axis]: 3 | |||
| Pay vs Performance Disclosure [Table] | |||
| Compensation Actually Paid vs. Other Measure [Text Block] | |||
| Measure Name | Non-GAAP Earnings Per Share | ||
| Measure [Axis]: 4 | |||
| Pay vs Performance Disclosure [Table] | |||
| Measure Name | Pipeline Milestones | ||
| Mr.Viehbacher [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| PEO Total Compensation Amount | $ 30,488,593 | $ 0 | $ 0 |
| PEO Actually Paid Compensation Amount | $ 27,551,849 | 0 | 0 |
| PEO Name | Mr. Viehbacher | ||
| Mr.Vounatsos [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| PEO Total Compensation Amount | $ 26,625,221 | 17,689,665 | 18,659,829 |
| PEO Actually Paid Compensation Amount | $ 5,898,711 | 15,211,025 | 8,578,367 |
| PEO Name | Mr. Vounatsos | ||
| PEO [Member] | Mr.Viehbacher [Member] | Stock Awards And Option Awards [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | $ 30,000,655 | 0 | 0 |
| PEO [Member] | Mr.Viehbacher [Member] | YearEnd For Awards Granted During The Year [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 27,063,911 | ||
| PEO [Member] | Mr.Viehbacher [Member] | YearOverYear Increase Or Decrease Of Unvested Awards Granted In Prior Years [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 0 | ||
| PEO [Member] | Mr.Viehbacher [Member] | Prior Fiscal YearEnd For Awards That Vested During The Year [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 0 | ||
| PEO [Member] | Mr.Viehbacher [Member] | Total Equity Award Adjustments [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 27,063,911 | ||
| PEO [Member] | Mr.Viehbacher [Member] | YearOverYear Change In Fair Value Of Equity Awards [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 27,063,911 | 0 | 0 |
| PEO [Member] | Mr.Vounatsos [Member] | Stock Awards And Option Awards [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 15,389,732 | 14,084,314 | 13,887,064 |
| PEO [Member] | Mr.Vounatsos [Member] | YearEnd For Awards Granted During The Year [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 1,996,870 | 10,985,776 | 8,893,002 |
| PEO [Member] | Mr.Vounatsos [Member] | YearOverYear Increase Or Decrease Of Unvested Awards Granted In Prior Years [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | (6,247,880) | (687,744) | (3,618,885) |
| PEO [Member] | Mr.Vounatsos [Member] | Prior Fiscal YearEnd For Awards That Vested During The Year [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | (1,085,768) | 1,307,643 | (1,468,515) |
| PEO [Member] | Mr.Vounatsos [Member] | Total Equity Award Adjustments [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | (5,336,778) | 11,605,674 | 3,805,602 |
| PEO [Member] | Mr.Vounatsos [Member] | YearOverYear Change In Fair Value Of Equity Awards [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | (5,336,778) | 11,605,674 | 3,805,602 |
| Non-PEO NEO [Member] | Stock Awards And Option Awards [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 4,223,226 | 4,105,942 | 4,158,006 |
| Non-PEO NEO [Member] | YearEnd For Awards Granted During The Year [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 3,809,706 | 3,295,987 | 2,904,843 |
| Non-PEO NEO [Member] | YearOverYear Increase Or Decrease Of Unvested Awards Granted In Prior Years [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | (244,173) | (156,359) | (741,018) |
| Non-PEO NEO [Member] | Prior Fiscal YearEnd For Awards That Vested During The Year [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | (251,296) | 286,695 | (167,520) |
| Non-PEO NEO [Member] | Total Equity Award Adjustments [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 3,314,236 | 3,426,323 | 1,996,306 |
| Non-PEO NEO [Member] | YearOverYear Change In Fair Value Of Equity Awards [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | $ 3,314,236 | $ 3,426,323 | $ 1,996,306 |
