Acquisitions - Narrative (Details) $ / shares in Units, $ in Millions			3 Months Ended			9 Months Ended		12 Months Ended
	Jul. 02, 2024 USD ($)	Sep. 26, 2023 USD ($) ft² $ / shares	Dec. 31, 2024 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Business Acquisition [Line Items]
Share-based compensation expense				$ (75.0)	$ (64.8)	$ (224.0)	$ (217.8)
Current portion of contingent consideration obligations				287.1		287.1		$ 0.0
Noncurrent portion of contingent consideration obligations				221.8		221.8
Goodwill				6,485.8		6,485.8		6,219.2
Selling, general and administrative				588.4	788.2	1,723.7	1,941.2
Net income				388.5	(68.3)	1,365.5	912.6
Cost of sales, excluding amortization and impairment of acquired intangible assets				638.7	659.6	1,726.9	1,915.1
Felzartamab And Izastobart/HIB210 | Milestone Payment, Future Development | Human Immunology Biosciences Pre-Existing In License Commitments
Business Acquisition [Line Items]
Contingent consideration obligations	$ 130.0
Felzartamab And Izastobart/HIB210 | Milestone Payment, Regulatory | Human Immunology Biosciences Pre-Existing In License Commitments
Business Acquisition [Line Items]
Contingent consideration obligations	230.0
Felzartamab And Izastobart/HIB210 | Milestone Payment, Commercial | Human Immunology Biosciences Pre-Existing In License Commitments
Business Acquisition [Line Items]
Contingent consideration obligations	640.0
Forecast
Business Acquisition [Line Items]
Outstanding equity awards			$ 983.9
Research and development
Business Acquisition [Line Items]
Share-based compensation expense				69.8	217.1	124.5	276.3
Selling, general and administrative
Business Acquisition [Line Items]
Share-based compensation expense				61.3	234.9	150.9	333.4
Human Immunology Biosciences
Business Acquisition [Line Items]
Total transaction value	1,137.3
Range of outcomes, value, high	650.0
Non-vested equity awards	74.5
Share-based compensation expense	56.4			56.4	0.0	56.4	0.0
Working capital adjustment	43.7
Contingent consideration obligations	485.1
Current portion of contingent consideration obligations	279.3
Noncurrent portion of contingent consideration obligations	205.8
Intangible assets:	1,600.0
Goodwill	256.5
Acquisition related costs				2.8		2.8
Operating lease liabilities	1.2
Operating lease assets	$ 1.2
Human Immunology Biosciences | Discount rate
Business Acquisition [Line Items]
Measurement input	0.145
Human Immunology Biosciences | Measurement Input, Probability Rate
Business Acquisition [Line Items]
Discount rate	0.670
Human Immunology Biosciences | Previously Reported
Business Acquisition [Line Items]
Total transaction value	$ 1,150.0
Human Immunology Biosciences | Minimum | Discount rate
Business Acquisition [Line Items]
Discount rate	0.062
Human Immunology Biosciences | Maximum | Discount rate
Business Acquisition [Line Items]
Discount rate	0.070
Human Immunology Biosciences | Maximum | Phase 3 Clinical Trial, Felzartamab One
Business Acquisition [Line Items]
Current portion of contingent consideration obligations	$ 150.0
Human Immunology Biosciences | Maximum | Phase 3 Clinical Trial, Felzartamab Two
Business Acquisition [Line Items]
Current portion of contingent consideration obligations	150.0
Human Immunology Biosciences | Research and development
Business Acquisition [Line Items]
Share-based compensation expense	42.5
Human Immunology Biosciences | Selling, general and administrative
Business Acquisition [Line Items]
Share-based compensation expense	13.9
Human Immunology Biosciences | In-process research and development
Business Acquisition [Line Items]
Intangible assets:				1,600.0		1,600.0
Human Immunology Biosciences | Other clinical programs
Business Acquisition [Line Items]
Intangible assets:	$ 7.9
Reata Pharmaceuticals, Inc
Business Acquisition [Line Items]
Total transaction value		$ 6,602.9
Share-based compensation expense				0.0	$ 387.0	0.0	$ 387.0
Goodwill		$ 469.2		469.2		469.2
Price per share (in dollars per share) | $ / shares		$ 172.50
Equity compensation pre-acquisition services		$ 590.5
Operating expenses		393.4
Selling, general and administrative		196.4
Research and development expense asset acquired		197.0
Inventory		$ 1,300.0		1,259.0		1,259.0
Inventory amortization period		4 years
Intangible assets discount rate		14.30%
Operating lease area | ft²		327,400
Lease term		16 years
Operating lease liabilities		$ 151.8		151.8		151.8
Remaining lease term		15 years
Operating lease assets		$ 121.2		121.2		121.2
Reata Pharmaceuticals, Inc | Fair Value Adjustment to Inventory
Business Acquisition [Line Items]
Net income				50.9		185.1
Reata Pharmaceuticals, Inc | Clinical Inventory | Fair Value Adjustment to Inventory
Business Acquisition [Line Items]
Cost of sales, excluding amortization and impairment of acquired intangible assets				2.5		48.5
Reata Pharmaceuticals, Inc | Secured Debt | The Credit Facility | Line of Credit
Business Acquisition [Line Items]
Long-term debt, gross		1,000.0
Reata Pharmaceuticals, Inc | Selling, general and administrative
Business Acquisition [Line Items]
Acquisition cost expensed								$ 26.3
Reata Pharmaceuticals, Inc | Completed technology for SKYCLARYS (U.S.)
Business Acquisition [Line Items]
Intangible assets:		4,200.0		4,200.0		4,200.0
Reata Pharmaceuticals, Inc | In-process research and development
Business Acquisition [Line Items]
Intangible assets:		2,300.0		2,300.0		2,300.0
Reata Pharmaceuticals, Inc | Priority review voucher
Business Acquisition [Line Items]
Intangible assets:		100.0		100.0		100.0
Reata Pharmaceuticals, Inc | Other clinical programs
Business Acquisition [Line Items]
Intangible assets:		$ 40.0		$ 40.0		$ 40.0