Fair Value Measurements - Schedule of Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Available-for-sale debt securities:
Available-for-sale debt securities	$ 6,614.9	$ 3,689.1
Corporate bonds
Available-for-sale debt securities:
Available-for-sale debt securities	5,924.8	3,090.3
U.S. government and government agency obligations
Available-for-sale debt securities:
Available-for-sale debt securities	101.7	128.9
Sovereign bonds
Available-for-sale debt securities:
Available-for-sale debt securities	65.1	66.3
Commercial paper
Available-for-sale debt securities:
Available-for-sale debt securities	272.6	276.1
Certificates of deposit
Available-for-sale debt securities:
Available-for-sale debt securities	231.7	127.5
Asset-backed securities
Available-for-sale debt securities:
Available-for-sale debt securities	19.0
Measured on a recurring basis
Available-for-sale debt securities:
Total marketable securities	7,986.5	4,528.9
Measured on a recurring basis | Unrestricted
Available-for-sale debt securities:
Equity securities	35.7	48.3
Measured on a recurring basis | Restricted
Available-for-sale debt securities:
Equity securities	1,335.9	791.5
Measured on a recurring basis | Corporate bonds
Available-for-sale debt securities:
Available-for-sale debt securities	5,924.8	3,090.3
Measured on a recurring basis | U.S. government and government agency obligations
Available-for-sale debt securities:
Available-for-sale debt securities	101.7	128.9
Measured on a recurring basis | Sovereign bonds
Available-for-sale debt securities:
Available-for-sale debt securities	65.1	66.3
Measured on a recurring basis | Commercial paper
Available-for-sale debt securities:
Available-for-sale debt securities	272.6	276.1
Measured on a recurring basis | Certificates of deposit
Available-for-sale debt securities:
Available-for-sale debt securities	231.7	127.5
Measured on a recurring basis | Asset-backed securities
Available-for-sale debt securities:
Available-for-sale debt securities	19.0
Measured on a recurring basis | Level 1
Available-for-sale debt securities:
Total marketable securities	1,371.6	839.8
Measured on a recurring basis | Level 1 | Unrestricted
Available-for-sale debt securities:
Equity securities	35.7	48.3
Measured on a recurring basis | Level 1 | Restricted
Available-for-sale debt securities:
Equity securities	1,335.9	791.5
Measured on a recurring basis | Level 1 | Corporate bonds
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 1 | U.S. government and government agency obligations
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 1 | Sovereign bonds
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 1 | Commercial paper
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 1 | Certificates of deposit
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Measured on a recurring basis | Level 1 | Asset-backed securities
Available-for-sale debt securities:
Available-for-sale debt securities	0.0
Measured on a recurring basis | Level 2
Available-for-sale debt securities:
Total marketable securities	6,614.9	3,689.1
Measured on a recurring basis | Level 2 | Unrestricted
Available-for-sale debt securities:
Equity securities	0.0	0.0
Measured on a recurring basis | Level 2 | Restricted
Available-for-sale debt securities:
Equity securities	0.0	0.0
Measured on a recurring basis | Level 2 | Corporate bonds
Available-for-sale debt securities:
Available-for-sale debt securities	5,924.8	3,090.3
Measured on a recurring basis | Level 2 | U.S. government and government agency obligations
Available-for-sale debt securities:
Available-for-sale debt securities	101.7	128.9
Measured on a recurring basis | Level 2 | Sovereign bonds
Available-for-sale debt securities:
Available-for-sale debt securities	65.1	66.3
Measured on a recurring basis | Level 2 | Commercial paper
Available-for-sale debt securities:
Available-for-sale debt securities	272.6	276.1
Measured on a recurring basis | Level 2 | Certificates of deposit
Available-for-sale debt securities:
Available-for-sale debt securities	231.7	$ 127.5
Measured on a recurring basis | Level 2 | Asset-backed securities
Available-for-sale debt securities:
Available-for-sale debt securities	$ 19.0