CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net income (loss)	$ 244.8	$ (289.5)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	25.0	20.7
Share-based compensation expense (benefit)	82.6	(8.0)
Impairments of investments in privately-held companies	5.6	0.0
Intangible asset impairment charges	0.0	8.8
Other	(13.9)	(37.0)
Changes in operating assets and liabilities:
Accounts receivable	(20.6)	(5.3)
Inventories	10.6	4.4
Accounts payable and accrued expenses	2.6	(3.0)
Other assets and liabilities	41.9	(185.6)
Net cash provided by (used in) operating activities	378.6	(494.5)
Cash flows from investing activities:
Purchases of property, plant, and equipment	(31.2)	(45.4)
Sales/maturities of held-to-maturity investments	0.0	38.2
Purchases of available-for-sale investments	(1,094.3)	(519.0)
Sales/maturities of available-for-sale investments	708.3	430.3
Sales of investments in equity securities	14.2	0.0
Purchase of investments in privately-held companies	0.0	(7.0)
Net cash used in investing activities	(403.0)	(102.9)
Cash flows from financing activities:
Proceeds from line of credit	0.0	800.0
Repayment of line of credit	(50.0)	0.0
Payments of debt issuance costs	0.0	(0.7)
Proceeds from the exercise of stock options	22.4	9.9
Proceeds from the issuance of stock under employee stock purchase plan	2.5	2.2
Restricted stock units withheld for taxes	(3.5)	(1.9)
Net cash (used in) provided by financing activities	(28.6)	809.5
Net (decrease) increase in cash and cash equivalents	(53.0)	212.1
Cash and cash equivalents, beginning of period	738.4	669.2
Cash and cash equivalents, end of period	685.4	881.3
Supplemental cash flow information:
Cash paid for interest	12.4	20.6
Cash paid for income taxes	44.0	62.7
Non-cash investing and financing activities:
Non-cash additions to property, plant, and equipment	$ 6.9	$ 4.0