Interim Financial Statements - Schedule of Balance Sheet Data (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued expenses and other current liabilities	$ 1,257.0	$ 1,211.4
Other liabilities - Sanofi	103.8	85.0
Other noncurrent liabilities	457.9	317.7
Sanofi
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	380.2	310.5
Deferred revenue, noncurrent	37.8	27.7
Other noncurrent liabilities	390.3	482.0
Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	81.3	71.6
Deferred revenue, noncurrent	$ 67.0	77.6
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
Other noncurrent liabilities		286.0
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
Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued expenses and other current liabilities		124.6
Other liabilities - Sanofi		85.0
Other noncurrent liabilities		31.7
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)