Stockholders' Equity - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended			6 Months Ended
	May 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Mar. 31, 2019	Jun. 30, 2020	Nov. 30, 2019
Class of Stock [Line Items]
Treasury stock, shares acquired (in shares)	9,806,805
Cost of treasury stock received	$ 5,000,000,000	$ 5,071,800,000	$ 336,000,000.0	$ 54,000,000.0
Sanofi
Class of Stock [Line Items]
Number of shares sold (in shares)	13,014,646
Common Stock, shares outstanding (in shares)	400,000
Share Repurchase Program
Class of Stock [Line Items]
Share repurchase program, authorized amount						$ 1,000,000,000.0
Treasury stock, shares acquired (in shares)		0			719,167
Remaining authorized repurchase amount		$ 473,100,000			$ 473,100,000
Cost of treasury stock received					$ 272,800,000