XML 72 R34.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Equity (Tables) | 3 Months Ended
--- | ---
Mar. 31, 2018
Equity [Abstract] |
Reconciliation of equity attributable to noncontrolling interests | The following table reconciles equity (deficit) attributable to noncontrolling interests (NCI):
| For the Three Months Ended March 31,
(In millions) | 2018 |  | 2017
NCI, beginning of period | $ | (14.7 | ) |  | $ | (11.5 | )
Net income (loss) attributable to NCI, net of tax | (1.7 | ) |  | (0.1 | )
Translation adjustment and other | 0.2 |  |  | — |
NCI, end of period | $ | (16.2 | ) |  | $ | (11.6 | )

X
- Definition Reconciliation of equity attributable to noncontrolling interests. + References No definition available. + Details
Name: | biib_ReconciliationOfEquityAttributableToNoncontrollingInterestsTableTextBlock
Namespace Prefix: | biib_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_EquityAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration