Fair Value Measurements - Financial Instruments at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Liabilities:
Goodwill	$ 3,529.1	$ 3,490.4	$ 2,999.4
Rare Diseases reporting unit
Liabilities:
Goodwill	208.9
Recurring | Level 1
Assets:
Investment securities	0.1	0.1
Total assets	0.1	0.1
Liabilities:
Total liabilities	0.0	0.0
Recurring | Level 1 | Foreign currency forward contracts
Assets:
Foreign currency forward contracts	0.0	0.0
Liabilities:
Foreign currency forward contracts	0.0
Recurring | Level 1 | Cross-currency swap
Liabilities:
Foreign currency forward contracts	0.0	0.0
Recurring | Level 1 | Interest rate swap agreements
Assets:
Interest rate swap agreements	0.0	0.0
Liabilities:
Foreign currency forward contracts	0.0	0.0
Recurring | Level 2
Assets:
Investment securities	0.0	0.0
Total assets	31.1	54.7
Liabilities:
Total liabilities	186.4	101.3
Recurring | Level 2 | Foreign currency forward contracts
Assets:
Foreign currency forward contracts	0.6	4.2
Liabilities:
Foreign currency forward contracts	2.7	5.2
Recurring | Level 2 | Cross-currency swap
Liabilities:
Foreign currency forward contracts	172.0	96.1
Recurring | Level 2 | Interest rate swap agreements
Assets:
Interest rate swap agreements	30.5	50.5
Liabilities:
Foreign currency forward contracts	11.7	0.0
Recurring | Level 3
Assets:
Investment securities	0.0	0.0
Total assets	0.0	0.0
Liabilities:
Total liabilities	0.0	0.0
Recurring | Level 3 | Foreign currency forward contracts
Assets:
Foreign currency forward contracts	0.0	0.0
Liabilities:
Foreign currency forward contracts	0.0	0.0
Recurring | Level 3 | Cross-currency swap
Liabilities:
Foreign currency forward contracts	0.0	0.0
Recurring | Level 3 | Interest rate swap agreements
Assets:
Interest rate swap agreements	0.0	0.0
Liabilities:
Foreign currency forward contracts	0.0	0.0
Nonrecurring | Level 1
Assets:
Goodwill	0.0	0.0
Total assets	0.0	0.0
Nonrecurring | Level 2
Assets:
Goodwill	0.0	0.0
Total assets	0.0	0.0
Nonrecurring | Level 3
Assets:
Goodwill	118.9	0.0
Total assets	118.9	$ 0.0
Nonrecurring | Level 3 | Rare Diseases reporting unit
Assets:
Goodwill	$ 118.9