Collaboration Agreements (Details) shares in Millions			1 Months Ended											12 Months Ended
	Mar. 21, 2014 USD ($) Collaborative_Arrangement	Dec. 02, 2013 product_candidate	Feb. 29, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jul. 31, 2015 USD ($)	Jun. 30, 2015 USD ($) shares	Apr. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($) Amino_Acid_Target research_targets	Jan. 31, 2014 USD ($) data_package product_candidate	Apr. 30, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2015 USD ($) discovery_stage_program	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Selling, general and administrative														$ 2,305,400,000	$ 2,027,900,000	$ 1,684,500,000
Celgene
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Allocation of cost, as a percentage							70.00%
Acceleron Pharma Inc
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees														0	0	0	$ 70,000,000
Milestone payments made														$ 0	$ 0	17,000,000	27,500,000
Percentage of equity investment ownership				14.00%					14.00%					14.00%	14.00%
Additional equity investments made														$ 0	$ 52,400,000	10,000,000	30,500,000
Equity investment				$ 224,900,000					$ 179,700,000					224,900,000	179,700,000
Acceleron Pharma Inc | ACE-011 program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront and milestone payments received														367,000,000
Acceleron Pharma Inc | ACE-011 - discovery stage programs
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront and milestone payments received														$ 348,000,000
Number of programs | discovery_stage_program														3
Acceleron Pharma Inc | ACE-536 program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront and milestone payments received														$ 217,500,000
Acceleron Pharma Inc | ACE-536 first discovery stage program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront and milestone payments received														170,800,000
Acceleron Pharma Inc | ACE-536 second discovery stage program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront and milestone payments received														148,800,000
Acceleron Pharma Inc | ACE-536 each additional discovery stage program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront and milestone payments received														125,400,000
Agios Pharmaceuticals, Inc.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments									$ 20,000,000					120,000,000
Upfront fees														9,000,000	0	0	121,200,000
Milestone payments made														$ 0	$ 0	0	0
Percentage of equity investment ownership				13.00%					14.00%					13.00%	14.00%
Additional equity investments made														$ 0	$ 38,300,000	12,800,000	37,500,000
Equity investment				$ 340,400,000					$ 587,400,000					340,400,000	587,400,000
Agios Pharmaceuticals, Inc. | AG-881
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees								$ 10,000,000
Contingent milestone payments to be made								70,000,000
Agios Pharmaceuticals, Inc. | AG-881 | Manufacturing rights
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees								1,000,000
Agios Pharmaceuticals, Inc. | Research and development payments | AG-881
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees								9,000,000
Epizyme
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees														0	0	0	65,000,000
Research and development, period						3 years
Collaboration agreement, termination of agreement, period						120 days
Milestone payments made														$ 0	$ 0	25,000,000	0
Percentage of equity investment ownership				9.00%					11.00%					9.00%	11.00%
Additional equity investments made														$ 0	$ 9,900,000	1,000,000	25,000,000
Equity investment				$ 58,900,000					$ 69,300,000					58,900,000	69,300,000
Epizyme | Amended Agreement with Epizyme
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees						$ 10,000,000
Epizyme | Developmental milestone | Amended Agreement with Epizyme
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments						75,000,000
Epizyme | Regulatory milestone | Amended Agreement with Epizyme
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments						365,000,000
Epizyme | Regulatory milestone | DOT1L Program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments						100,000,000
Epizyme | Sales milestone | Amended Agreement with Epizyme
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments						170,000,000
Epizyme | Clinical development milestone | DOT1L Program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments						$ 35,000,000
Sutro Biopharma, Inc
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees										$ 95,000,000			$ 35,000,000	0	72,600,000	0	26,300,000
Research and development, period										3 years
Research and development additional, period										1 year 6 months
Collaboration agreement, termination of agreement, period										120 days
Collaboration agreement, number of projects | research_targets										6
Ownership percentage										15.00%
Collaboration agreement, performance evaluation | Amino_Acid_Target										5
Milestone payments made														$ 0	$ 0	0	0
Percentage of equity investment ownership				16.00%					15.00%					16.00%	15.00%
Additional equity investments made														$ 0	$ 11,900,000	1,700,000	4,000,000
Equity investment				$ 17,600,000					$ 17,600,000					17,600,000	17,600,000
Sutro Biopharma, Inc | Collaborative arrangement, antibody drug conjugate (ADC)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments													204,000,000
Sutro Biopharma, Inc | Collaborative arrangement, bispecific antibody construct (BAC)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments													$ 279,000,000
Sutro Biopharma, Inc | Collaborative agreement, research and manufacturing
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments										$ 75,000,000
Sutro Biopharma, Inc | Regulatory approval
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments										$ 275,000,000
Bluebird
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees							$ 25,000,000							0	0	74,700,000
Contingent milestone payments to be made							$ 230,000,000
Collaboration agreement, termination of agreement, period							90 days
Milestone payments made														0	0	0
Additional equity investments made														0	0	0
FORMA Therapeutics Holdings, LLC
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees														59,000,000	225,000,000	52,800,000
Collaboration agreement, number of additional agreement | Collaborative_Arrangement	2
Collaboration agreement, term of additional agreement	2 years
Collaboration agreement, payment to exercise additional agreement	$ 375,000,000
Milestone payments made														0	0	0
Additional equity investments made														0	0	0
FORMA Therapeutics Holdings, LLC | Regulatory approval
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments												$ 315,000,000
Research and development, period												4 years
FORMA Therapeutics Holdings, LLC | Research and development payments
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees	$ 225,000,000											$ 200,000,000
FORMA Therapeutics Holdings, LLC | License payments
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments												$ 430,000,000
Upfront fees								20,000,000						68,000,000
FORMA Therapeutics Holdings, LLC | Option to license rights to current and future drug candidates
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement, term of additional agreement	3 years 6 months
Acetylon
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees														0	0	50,000,000	0
Milestone payments made														$ 0	$ 0	0	0
Percentage of equity investment ownership				14.00%					10.00%					14.00%	10.00%
Additional equity investments made														$ 15,000,000	$ 0	10,000,000	$ 15,000,000
Equity investment				$ 30,000,000					$ 25,000,000					30,000,000	25,000,000
Acetylon | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments														1,100,000,000
OncoMed
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees														2,500,000	2,500,000	155,000,000
Milestone payments made														$ 70,000,000	$ 0	0
Effective notice period required to be served for termination of agreement														120 days
Codevelopment sharing of global development costs														33.33%
Percentage of equity investment ownership				5.00%					5.00%					5.00%	5.00%
Additional equity investments made														$ 0	$ 0	22,200,000
Equity investment				$ 33,100,000					$ 32,000,000					$ 33,100,000	32,000,000
OncoMed | Subsequent Event
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments made			$ 70,000,000
OncoMed | Celgene
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Codevelopment sharing of global development costs														66.67%
OncoMed | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of programs | discovery_stage_program														5
Number of anti-cancer stem cell products candidates from pipeline | product_candidate		6
Worldwide licensing rights for Anti-CSC therapeutic candidates, term		60 days
OncoMed | RSPO-LGR CSC pathway or another CSC Pathway | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of programs | discovery_stage_program														4
OncoMed | Demcizumab | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent milestone payments to be made														$ 790,000,000
OncoMed | Anti-DLL4/VEGF | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent milestone payments to be made														505,000,000
OncoMed | Other four biological programs
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent milestone payments to be made														440,000,000
OncoMed | Small molecule program | Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent milestone payments to be made														100,000,000
NantBioScience
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees											$ 50,000,000			0	50,000,000
Milestone payments made														$ 0	$ 0
Effective notice period required to be served for termination of agreement											30 days
Aggregate collaboration agreement payments											$ 75,000,000
Number of product candidates from pipeline | product_candidate											2
Percentage of equity investment ownership				13.00%					14.00%		14.00%			13.00%	14.00%
Potential future investment											$ 50,000,000
Collaboration agreement, agreement termination milestones, number of product candidates | product_candidate											4
Collaboration agreement, agreement termination milestones, number of data packages for product candidates | data_package											10
Collaboration agreement, agreement termination milestones, expiration period											10 years
Selling, general and administrative											$ 25,000,000
Additional equity investments made											$ 90,000,000			$ 0	$ 90,000,000
Equity investment				$ 90,000,000					$ 90,000,000					$ 90,000,000	90,000,000
MedImmune
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees								$ 450,000,000
Collaboration agreement, termination of agreement, period								9 months
Future cost responsibility, as a percentage														75.00%
Forecasted royalty rate														50.00%
Royalty decrease period								4 years
MedImmune | MEDI4736
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Future royalty rate														70.00%
Lycera
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments							$ 190,000,000
Upfront fees							$ 82,500,000							$ 87,000,000
Collaboration agreement, termination of agreement, period							6 months
Milestone payments made														$ 0
Percentage of equity investment ownership				8.00%										8.00%
Additional equity investments made														$ 10,000,000
Equity investment				$ 10,000,000										10,000,000
Initial term of agreement							3 years
Lycera | Research and development payments
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees							$ 69,500,000
Lycera | Research and development payments | Other non-current assets
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees							13,000,000
Equity investment							10,000,000
Payment made for warrant rights							3,000,000
Lycera | License payments
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees				$ 17,500,000
Juno Therapeutics
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees							$ 150,000,000							575,100,000
Collaboration agreement, termination of agreement, period							120 days
Ownership percentage							9.00%
Milestone payments made														$ 0
Percentage of equity investment ownership				9.00%										9.00%
Additional equity investments made														$ 424,900,000
Equity investment				$ 401,800,000										401,800,000
Initial term of agreement							10 years
Allocation of cost, as a percentage							30.00%
Payment made to Juno							$ 1,000,000,000
Investment in Juno, shares owned | shares							9.1
Available-for-sale securities in Juno							$ 424,900,000
Juno Therapeutics | Research and development payments
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees							$ 425,100,000
Nurix
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees					$ 149,800,000									149,800,000
Ownership percentage					11.00%
Milestone payments made														$ 0
Percentage of equity investment ownership				11.00%										11.00%
Additional equity investments made														$ 17,000,000
Equity investment				$ 17,000,000										17,000,000
Investment in Nurix					$ 17,000,000
First option to license future programs					45 days
Second option to license future programs					4 years
Nurix | License payments
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments					$ 405,000,000
Other Collaboration Arrangements
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fees														69,800,000	103,500,000	243,300,000
Milestone payments made														8,000,000	8,300,000	1,000,000
Additional equity investments made														50,000,000	55,700,000	$ 71,700,000
Equity investment				$ 105,400,000					$ 132,700,000					105,400,000	$ 132,700,000
Other Collaboration Arrangements | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent milestone payments to be made														$ 120,000,000