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Reserves for Discounts and Allowances (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015
Analysis of the amount of, and change in, reserves |
Balance as of December 31, 2014 | $ 483.8 us-gaap_ValuationAllowancesAndReservesBalance
Current provisions relating to sales in current year | 553.2 biib_CurrentProvisionsToProductRevenueReservesRelatingToSalesInCurrentYear
Adjustments relating to prior years | (18.5)biib_AdjustmentsToProductRevenueReservesRelatingToSalesInPriorYears
Payments/credits relating to sales in current year | (217.7)biib_PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToCurrentYear
Payments/credits relating to sales in prior years | (216.6)biib_PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToPriorYear
Balance as of March 31, 2015 | 584.2 us-gaap_ValuationAllowancesAndReservesBalance
Discounts |
Analysis of the amount of, and change in, reserves |
Balance as of December 31, 2014 | 47.6 us-gaap_ValuationAllowancesAndReservesBalance / us-gaap_ValuationAllowancesAndReservesTypeAxis = us-gaap_ReserveForCashDiscountMember
Current provisions relating to sales in current year | 101.8 biib_CurrentProvisionsToProductRevenueReservesRelatingToSalesInCurrentYear / us-gaap_ValuationAllowancesAndReservesTypeAxis = us-gaap_ReserveForCashDiscountMember
Adjustments relating to prior years | (2.4)biib_AdjustmentsToProductRevenueReservesRelatingToSalesInPriorYears / us-gaap_ValuationAllowancesAndReservesTypeAxis = us-gaap_ReserveForCashDiscountMember
Payments/credits relating to sales in current year | (50.3)biib_PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToCurrentYear / us-gaap_ValuationAllowancesAndReservesTypeAxis = us-gaap_ReserveForCashDiscountMember
Payments/credits relating to sales in prior years | (41.3)biib_PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToPriorYear / us-gaap_ValuationAllowancesAndReservesTypeAxis = us-gaap_ReserveForCashDiscountMember
Balance as of March 31, 2015 | 55.4 us-gaap_ValuationAllowancesAndReservesBalance / us-gaap_ValuationAllowancesAndReservesTypeAxis = us-gaap_ReserveForCashDiscountMember
Contractual Adjustments |
Analysis of the amount of, and change in, reserves |
Balance as of December 31, 2014 | 387.1 us-gaap_ValuationAllowancesAndReservesBalance / us-gaap_ValuationAllowancesAndReservesTypeAxis = biib_ContractualAdjustmentsMember
Current provisions relating to sales in current year | 441.2 biib_CurrentProvisionsToProductRevenueReservesRelatingToSalesInCurrentYear / us-gaap_ValuationAllowancesAndReservesTypeAxis = biib_ContractualAdjustmentsMember
Adjustments relating to prior years | (10.2)biib_AdjustmentsToProductRevenueReservesRelatingToSalesInPriorYears / us-gaap_ValuationAllowancesAndReservesTypeAxis = biib_ContractualAdjustmentsMember
Payments/credits relating to sales in current year | (166.7)biib_PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToCurrentYear / us-gaap_ValuationAllowancesAndReservesTypeAxis = biib_ContractualAdjustmentsMember
Payments/credits relating to sales in prior years | (170.7)biib_PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToPriorYear / us-gaap_ValuationAllowancesAndReservesTypeAxis = biib_ContractualAdjustmentsMember
Balance as of March 31, 2015 | 480.7 us-gaap_ValuationAllowancesAndReservesBalance / us-gaap_ValuationAllowancesAndReservesTypeAxis = biib_ContractualAdjustmentsMember
Returns |
Analysis of the amount of, and change in, reserves |
Balance as of December 31, 2014 | 49.1 us-gaap_ValuationAllowancesAndReservesBalance / us-gaap_ValuationAllowancesAndReservesTypeAxis = us-gaap_SalesReturnsAndAllowancesMember
Current provisions relating to sales in current year | 10.2 biib_CurrentProvisionsToProductRevenueReservesRelatingToSalesInCurrentYear / us-gaap_ValuationAllowancesAndReservesTypeAxis = us-gaap_SalesReturnsAndAllowancesMember
Adjustments relating to prior years | (5.9)biib_AdjustmentsToProductRevenueReservesRelatingToSalesInPriorYears / us-gaap_ValuationAllowancesAndReservesTypeAxis = us-gaap_SalesReturnsAndAllowancesMember
Payments/credits relating to sales in current year | (0.7)biib_PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToCurrentYear / us-gaap_ValuationAllowancesAndReservesTypeAxis = us-gaap_SalesReturnsAndAllowancesMember
Payments/credits relating to sales in prior years | (4.6)biib_PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToPriorYear / us-gaap_ValuationAllowancesAndReservesTypeAxis = us-gaap_SalesReturnsAndAllowancesMember
Balance as of March 31, 2015 | $ 48.1 us-gaap_ValuationAllowancesAndReservesBalance / us-gaap_ValuationAllowancesAndReservesTypeAxis = us-gaap_SalesReturnsAndAllowancesMember

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- Definition Current provisions to product revenue reserves relating to sales in current year. + References No definition available. + Details
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- Definition Payments/ returns applied against product revenue reserves relating to current year. + References No definition available. + Details
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- Definition Payments/ returns applied against product revenue reserves relating to prior year. + References No definition available. + Details
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- Definition Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 09 -Article 12 + Details
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