Business Overview and Summary of Significant Accounting Policies - Schedule of Balance Sheet Data (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued expenses and other current liabilities	$ 1,521.8	$ 1,211.4
Other liabilities - Sanofi	122.4	85.0
Sanofi
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	341.7	310.5
Deferred revenue, noncurrent	16.7	27.7
Other noncurrent liabilities	189.3	482.0
Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	236.0	71.6
Deferred revenue, noncurrent	41.1	77.6
Other noncurrent liabilities	$ 497.8	317.7
As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued expenses and other current liabilities		1,086.8
Other liabilities - Sanofi		0.0
As Previously Reported | Sanofi
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current		395.5
Deferred revenue, noncurrent		509.7
Other noncurrent liabilities		0.0
As Previously Reported | Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current		196.2
Deferred revenue, noncurrent		109.3
Other noncurrent liabilities		286.0
Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued expenses and other current liabilities		124.6
Other liabilities - Sanofi		85.0
Adjustments | Sanofi
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current		(85.0)
Deferred revenue, noncurrent		(482.0)
Other noncurrent liabilities		482.0
Adjustments | Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current		(124.6)
Deferred revenue, noncurrent		(31.7)
Other noncurrent liabilities		$ 31.7