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Consolidated Statements of Equity - USD ($) $ in Millions | Total | Preferred stock | Common stock | Additional paid-in capital | Accumulated other comprehensive income (loss) | Retained earnings | Treasury stock | Noncontrolling interests | Parent | 2016 Share Repurchase Program | 2016 Share Repurchase Program Treasury stock | 2011 Share Repurchase Program | 2011 Share Repurchase Program Treasury stock
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Beginning Balance at Dec. 31, 2014 | $ (10,814.0) | $ 0.0 | $ (0.1) | $ (4,196.2) | $ 59.5 | $ (9,283.9) | $ (2,611.7) |  |  |  |  |  |
Beginning Balance at Dec. 31, 2014 | 10,809.0 |  |  |  |  |  |  |  |  |  |  |  |
Beginning Balance at Dec. 31, 2014 |  |  |  |  |  |  |  | $ 5.0 |  |  |  |  |
Beginning Balance, shares at Dec. 31, 2014 |  | 0 | (257,100,000) |  |  |  | (22,600,000) |  |  |  |  |  |
Net income attributable to Biogen Inc. | 3,547.0 |  |  |  |  | 3,547.0 |  |  |  |  |  |  |
Net income (loss) attributable to noncontrolling interests, net of tax | 46.2 |  |  |  |  |  |  | 46.2 |  |  |  |  |
Net income | 3,593.2 |  |  |  |  |  |  |  |  |  |  |  |
Other comprehensive income (loss), net of tax | (164.5) |  |  |  | (164.5) |  |  |  |  |  |  |  |
Other comprehensive income (loss), net of tax | (164.5) |  |  |  |  |  |  | 0.0 |  |  |  |  |
Acquisition of noncontrolling interest | (10.9) |  |  |  |  |  |  | (10.9) | $ 0.0 |  |  |  |
Distribution to noncontrolling interest | (60.0) |  |  |  |  |  |  | (60.0) | 0.0 |  |  |  |
Repurchase of common stock, at cost | $ (5,000.0) |  |  |  |  |  | $ 5,000.0 |  |  |  |  |  |
Repurchase of common stock, at cost, shares | (16,800,000) |  |  |  |  |  | (16,800,000) |  |  |  |  |  |
Retirement of common stock pursuant to the 2016 Share Repurchase Program, at cost | $ 0.0 |  |  | 4,377.5 |  | 622.5 | $ 5,000.0 |  |  |  |  |  |
Retirement of common stock pursuant to the 2015 Share Repurchase Program, at cost, shares |  |  | 16,800,000 |  |  |  | 16,800,000 |  |  |  |  |  |
Issuance of common stock under stock option and stock purchase plans | 54.2 |  | $ 0.0 | 54.2 |  |  |  |  |  |  |  |  |
Issuance of common stock under stock option and stock purchase plans, shares |  |  | 300,000 |  |  |  |  |  |  |  |  |  |
Issuance of common stock under stock award plan | (125.1) |  | $ 0.0 | (125.1) |  |  |  |  |  |  |  |  |
Issuance of common stock under stock award plan |  |  | 600,000 |  |  |  |  |  |  |  |  |  |
Compensation related to share-based payments | 183.2 |  |  | 183.2 |  |  |  |  |  |  |  |  |
Tax benefit from share-based payments | (69.0) |  |  | (69.0) |  |  |  |  |  |  |  |  |
Ending Balance at Dec. 31, 2015 | (9,374.9) | $ 0.0 | $ (0.1) | 0.0 | (224.0) | (12,208.4) | $ (2,611.7) |  |  |  |  |  |
Ending Balance at Dec. 31, 2015 | 9,372.8 |  |  |  |  |  |  |  |  |  |  |  |
Ending Balance at Dec. 31, 2015 |  |  |  |  |  |  |  | 2.1 |  |  |  |  |
Ending Balance, shares at Dec. 31, 2015 |  | 0 | (241,200,000) |  |  |  | (22,600,000) |  |  |  |  |  |
Net income attributable to Biogen Inc. | 3,702.8 |  |  |  |  | 3,702.8 |  |  |  |  |  |  |
Net income (loss) attributable to noncontrolling interests, net of tax | (7.1) |  |  |  |  |  |  | (7.1) |  |  |  |  |
Net income | 3,695.7 |  |  |  |  |  |  |  |  |  |  |  |
Other comprehensive income (loss), net of tax | (95.9) |  |  |  | (95.9) |  |  |  |  |  |  |  |
Other comprehensive income (loss), net of tax | 95.8 |  |  |  |  |  |  | (0.1) |  |  |  |  |
Noncontrolling interest, increase (decrease) other | 1.5 |  |  |  |  |  |  | 1.5 | 0.0 |  |  |  |
Acquisition of noncontrolling interest | (0.6) |  |  |  |  |  |  | (0.6) | 0.0 |  |  |  |
Deconsolidation of noncontrolling interest | (7.5) |  |  |  |  |  |  | (7.5) | 0.0 |  |  |  |
Repurchase of common stock, at cost | (1,000.0) |  |  |  |  |  | $ (1,000.0) |  |  |  |  |  |
Repurchase of common stock, at cost, shares |  |  |  |  |  |  | (3,300,000) |  |  | (3,300,000) |  |  |
Retirement of common stock pursuant to the 2016 Share Repurchase Program, at cost | 0.0 |  | $ 0.0 | 164.9 |  | 835.1 | $ 1,000.0 |  |  |  |  |  |
Retirement of common stock pursuant to the 2015 Share Repurchase Program, at cost, shares |  |  | 3,300,000 |  |  |  | 3,300,000 |  |  |  |  |  |
Issuance of common stock under stock option and stock purchase plans | 43.7 |  | $ 0.0 | 43.7 |  |  |  |  |  |  |  |  |
Issuance of common stock under stock option and stock purchase plans, shares |  |  | 200,000 |  |  |  |  |  |  |  |  |  |
Issuance of common stock under stock award plan | (52.1) |  | $ 0.0 | (47.6) |  | (4.5) |  |  |  |  |  |  |
Issuance of common stock under stock award plan |  |  | 400,000 |  |  |  |  |  |  |  |  |  |
Compensation related to share-based payments | 169.4 |  |  | 169.4 |  |  |  |  |  |  |  |  |
Tax benefit from share-based payments | (0.6) |  |  | 0.6 |  |  |  |  |  |  |  |  |
Ending Balance at Dec. 31, 2016 | (12,128.6) | $ 0.0 | $ (0.1) | 0.0 | (319.9) | (15,071.6) | $ (2,611.7) |  |  |  |  |  |
Ending Balance at Dec. 31, 2016 | 12,140.1 |  |  |  |  |  |  |  |  |  |  |  |
Ending Balance at Dec. 31, 2016 | (11.5) |  |  |  |  |  |  | (11.5) |  |  |  |  |
Ending Balance, shares at Dec. 31, 2016 |  | 0 | (238,500,000) |  |  |  | (22,600,000) |  |  |  |  |  |
Net income attributable to Biogen Inc. | 2,539.1 |  |  |  |  | 2,539.1 |  |  |  |  |  |  |
Net income (loss) attributable to noncontrolling interests, net of tax | 131.0 |  |  |  |  |  |  | 131.0 |  |  |  |  |
Net income | 2,670.1 |  |  |  |  |  |  |  |  |  |  |  |
Other comprehensive income (loss), net of tax | 1.5 |  |  |  | 1.5 |  |  |  |  |  |  |  |
Other comprehensive income (loss), net of tax | 1.5 |  |  |  |  |  |  | 0.0 |  |  |  |  |
Noncontrolling interest, increase (decrease) other | 15.8 |  |  |  |  |  |  | 15.8 | 0.0 |  |  |  |
Distribution to noncontrolling interest | (150.0) |  |  |  |  |  |  | (150.0) | $ 0.0 |  |  |  |
Repurchase of common stock, at cost |  |  |  |  |  |  |  |  |  | $ (1,000.0) | $ (1,000.0) | $ (365.4) | $ (365.4)
Repurchase of common stock, at cost, shares |  |  |  |  |  |  |  |  |  | (3,700,000) | (3,700,000) | (1,200,000) | (1,200,000)
Retirement of common stock pursuant to the 2016 Share Repurchase Program, at cost | 0.0 |  | $ 0.0 | 36.0 |  | 964.0 | $ 1,000.0 |  |  |  |  |  |
Retirement of common stock pursuant to the 2015 Share Repurchase Program, at cost, shares |  |  | 3,700,000 |  |  |  | 3,700,000 |  |  |  |  |  |
Issuance of common stock under stock option and stock purchase plans | 40.5 |  | $ 0.0 | 40.5 |  | 0.0 |  |  |  |  |  |  |
Issuance of common stock under stock option and stock purchase plans, shares |  |  | 200,000 |  |  |  |  |  |  |  |  |  |
Issuance of common stock under stock award plan | $ (45.8) |  | $ 0.0 | (44.8) |  | (1.0) |  |  |  |  |  |  |
Issuance of common stock under stock award plan | 14,000 |  | 300,000 |  |  |  |  |  |  |  |  |  |
Compensation related to share-based payments | $ 138.1 |  |  | 138.1 |  |  |  |  |  |  |  |  |
Hemophilia spin-off adjustment | (852.8) |  |  |  |  | (852.8) |  |  |  |  |  |  |
Tax benefit | 17.5 |  |  |  |  | 17.5 |  |  |  |  |  |  |
Ending Balance at Dec. 31, 2017 | (12,598.1) | $ 0.0 | $ (0.1) | $ (97.8) | $ (318.4) | $ (15,810.4) | $ (2,977.1) |  |  |  |  |  |
Ending Balance at Dec. 31, 2017 | 12,612.8 |  |  |  |  |  |  |  |  |  |  |  |
Ending Balance at Dec. 31, 2017 | $ (14.7) |  |  |  |  |  |  | $ (14.7) |  |  |  |  |
Ending Balance, shares at Dec. 31, 2017 |  | 0 | (235,300,000) |  |  |  | (23,800,000) |  |  |  |  |  |

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