Fair Value Measurements - Schedule of Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Assets:
Available-for-sale debt securities	$ 12,533.9	$ 10,018.2
Corporate bonds
Assets:
Available-for-sale debt securities	6,398.0	6,684.4
U.S. government and government agency obligations
Assets:
Available-for-sale debt securities	4,833.4	2,939.4
Sovereign bonds
Assets:
Available-for-sale debt securities	57.2	64.1
Commercial paper
Assets:
Available-for-sale debt securities	636.8	121.1
Certificates of deposit
Assets:
Available-for-sale debt securities	521.4	182.0
Asset-backed securities
Assets:
Available-for-sale debt securities	87.1	27.2
Measured on a recurring basis
Assets:
Cash equivalents	928.1	1,662.8
Total assets	14,439.4	12,891.0
Liabilities:
Contingent consideration - CVRs	43.7
Measured on a recurring basis | Unrestricted
Assets:
Equity securities	864.5	24.6
Measured on a recurring basis | Restricted
Assets:
Equity securities	112.9	1,185.4
Measured on a recurring basis | Corporate bonds
Assets:
Available-for-sale debt securities	6,398.0	6,684.4
Measured on a recurring basis | U.S. government and government agency obligations
Assets:
Available-for-sale debt securities	4,833.4	2,939.4
Measured on a recurring basis | Sovereign bonds
Assets:
Available-for-sale debt securities	57.2	64.1
Measured on a recurring basis | Commercial paper
Assets:
Available-for-sale debt securities	636.8	121.1
Measured on a recurring basis | Certificates of deposit
Assets:
Available-for-sale debt securities	521.4	182.0
Measured on a recurring basis | Asset-backed securities
Assets:
Available-for-sale debt securities	87.1	27.2
Measured on a recurring basis | Level 1
Assets:
Cash equivalents	6.4	88.3
Total assets	983.8	1,298.3
Liabilities:
Contingent consideration - CVRs	0.0
Measured on a recurring basis | Level 1 | Unrestricted
Assets:
Equity securities	864.5	24.6
Measured on a recurring basis | Level 1 | Restricted
Assets:
Equity securities	112.9	1,185.4
Measured on a recurring basis | Level 1 | Corporate bonds
Assets:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 1 | U.S. government and government agency obligations
Assets:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 1 | Sovereign bonds
Assets:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 1 | Commercial paper
Assets:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 1 | Certificates of deposit
Assets:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 1 | Asset-backed securities
Assets:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 2
Assets:
Cash equivalents	921.7	1,574.5
Total assets	13,455.6	11,592.7
Liabilities:
Contingent consideration - CVRs	0.0
Measured on a recurring basis | Level 2 | Unrestricted
Assets:
Equity securities	0.0	0.0
Measured on a recurring basis | Level 2 | Restricted
Assets:
Equity securities	0.0	0.0
Measured on a recurring basis | Level 2 | Corporate bonds
Assets:
Available-for-sale debt securities	6,398.0	6,684.4
Measured on a recurring basis | Level 2 | U.S. government and government agency obligations
Assets:
Available-for-sale debt securities	4,833.4	2,939.4
Measured on a recurring basis | Level 2 | Sovereign bonds
Assets:
Available-for-sale debt securities	57.2	64.1
Measured on a recurring basis | Level 2 | Commercial paper
Assets:
Available-for-sale debt securities	636.8	121.1
Measured on a recurring basis | Level 2 | Certificates of deposit
Assets:
Available-for-sale debt securities	521.4	182.0
Measured on a recurring basis | Level 2 | Asset-backed securities
Assets:
Available-for-sale debt securities	87.1	27.2
Measured on a recurring basis | Level 3
Assets:
Cash equivalents	0.0	0.0
Total assets	0.0	0.0
Liabilities:
Contingent consideration - CVRs	43.7
Measured on a recurring basis | Level 3 | Unrestricted
Assets:
Equity securities	0.0	0.0
Measured on a recurring basis | Level 3 | Restricted
Assets:
Equity securities	0.0	0.0
Measured on a recurring basis | Level 3 | Corporate bonds
Assets:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 3 | U.S. government and government agency obligations
Assets:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 3 | Sovereign bonds
Assets:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 3 | Commercial paper
Assets:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 3 | Certificates of deposit
Assets:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 3 | Asset-backed securities
Assets:
Available-for-sale debt securities	$ 0.0	$ 0.0