2.2.0.7 true Overview (Details) (USD $) 0601 - Disclosure - Overview (Details) true false In Millions false false 1 USD false false USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 Pure Standard http://www.xbrl.org/2003/instance pure xbrli 0 USDEPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 $ 7 1 biib_OverviewTextualsAbstract biib false na duration Overview Textuals Abstract. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false xbrli:stringItemType string Overview Textuals Abstract. false 8 2 biib_InterestInSubsidiary biib false na duration Interest in subsidiary false false false false false false false false false false false verboselabel false 1 false true false false 1 1 false false false us-types:percentItemType pure Interest in subsidiary No authoritative reference available. false 1 2 false HundredThousands UnKnown UnKnown false true