CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 3,513.2	$ 2,115.8	$ 2,444.4
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	235.9	210.3	148.2
Non-cash compensation expense	432.0	464.3	427.4
Other non-cash items, net	(135.0)	(29.3)	12.1
Deferred taxes	75.6	(130.6)	(140.0)
Changes in assets and liabilities:
Increase in trade, Sanofi, and other accounts receivable	(1,356.1)	(523.7)	(236.4)
Increase in inventories	(529.4)	(335.5)	(387.9)
Decrease (increase) in prepaid expenses and other assets	114.9	(79.8)	(88.1)
Increase (decrease) in deferred revenue	148.1	139.5	(43.4)
Increase in accounts payable, accrued expenses, and other liabilities	118.9	599.0	58.8
Total adjustments	(895.1)	314.2	(249.3)
Net cash provided by operating activities	2,618.1	2,430.0	2,195.1
Cash flows from investing activities:
Purchases of marketable and other securities	(3,241.0)	(3,202.4)	(1,845.5)
Sales or maturities of marketable and other securities	3,785.0	1,604.2	775.6
Capital expenditures	(614.6)	(429.6)	(383.1)
Other	0.0	0.0	(10.0)
Net cash used in investing activities	(70.6)	(2,027.8)	(1,463.0)
Cash flows from financing activities:
Proceeds from issuance of long-term debt, net of issuance costs	1,981.9	0.0	0.0
Proceeds from bridge loan facility	1,500.0	0.0	0.0
Repayment of bridge loan facility	(1,500.0)	0.0	0.0
Proceeds from issuance of Common Stock	2,575.2	211.8	114.5
Payments in connection with Common Stock tendered for employee tax obligations	(680.8)	(188.0)	(187.2)
Repurchases of Common Stock	(5,846.8)	(275.9)	(4.4)
Net cash used in financing activities	(1,970.5)	(252.1)	(77.1)
Net increase in cash, cash equivalents, and restricted cash	577.0	150.1	655.0
Cash, cash equivalents, and restricted cash at beginning of period	1,630.3	1,480.2	825.2
Cash, cash equivalents, and restricted cash at end of period	2,207.3	1,630.3	1,480.2
Supplemental disclosure of cash flow information
Cash paid for interest (net of amounts capitalized)	23.2	25.0	22.3
Cash paid for income taxes	$ 188.1	$ 342.3	$ 205.6