XML 95 R64.htm IDEA: XBRL DOCUMENT v3.21.1

Share Repurchases (Details) - USD ($) shares in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Oct. 31, 2020
Class of Stock [Line Items]
Payments for repurchase of common stock	$ 600,000,000.0	$ 2,220,200,000
December 2019 Share Repurchase Program
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount			$ 5,000,000,000.0
Repurchase of common stock, at cost, shares		3.2
Payments for repurchase of common stock		$ 941,100,000
2019 Share Repurchase Program
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount		$ 5,000,000,000.0
Repurchase of common stock, at cost, shares		4.1
Payments for repurchase of common stock		$ 1,300,000,000
October 2020 Share Repurchase Program
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount				$ 5,000,000,000.0
Repurchase of common stock, at cost, shares	2.2
Payments for repurchase of common stock	$ 600,000,000.0
Amount remaining under 2019 Share Repurchase Program	$ 4,000,000,000.0

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ClassOfStockLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The cash outflow to reacquire common stock during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3291-108585

+ Details

Name:	us-gaap_PaymentsForRepurchaseOfCommonStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of stock repurchase plan authorized.

+ References

No definition available.

+ Details

Name:	us-gaap_StockRepurchaseProgramAuthorizedAmount1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Amount remaining of a stock repurchase plan authorized.

+ References

No definition available.

+ Details

Name:	us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Number of shares that have been repurchased during the period and are being held in treasury.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_TreasuryStockSharesAcquired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_ShareRepurchaseProgramAxis=biib_December2019ShareRepurchaseProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ShareRepurchaseProgramAxis=biib_March2019ShareRepurchaseProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ShareRepurchaseProgramAxis=biib_October2020ShareRepurchaseProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: