Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net income	$ 31.1	$ 34.4
Adjustments to reconcile net income to net cash provided by operating activities:
Share-based compensation expense	33.9	70.4
Depreciation, amortization, and accretion	48.7	55.7
Other	(2.2)	1.7
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable, net	108.6	170.8
Prepaid expenses and other assets	0.5	(11.7)
Accounts payable	10.1	(31.2)
Accrued compensation	(54.9)	(14.1)
Income taxes payable	(5.7)	(7.6)
Other accrued liabilities	(27.9)	(51.1)
Deferred revenue	17.2	53.8
Net cash provided by operating activities	159.4	271.1
Cash flows from investing activities:
Purchases of property and equipment	(27.9)	(42.2)
Purchases of available-for-sale debt securities	(884.4)	(8.1)
Proceeds from sales of available-for-sale debt securities	232.8	968.0
Proceeds from maturities and redemptions of available-for-sale debt securities	578.3	215.4
Purchases of equity securities	(5.1)	(2.0)
Proceeds from sales of equity securities	2.2	3.3
Subsequent payments related to acquisitions in prior years	0.0	(22.2)
Net cash (used in) provided by investing activities	(104.1)	1,112.2
Cash flows from financing activities:
Repurchase and retirement of common stock	(2.9)	(754.2)
Proceeds from issuance of common stock	29.5	29.3
Payment of dividends	(66.2)	(62.1)
Change in customer financing arrangement	0.0	(16.6)
Payment of debt	(350.0)	0.0
Net cash used in financing activities	(389.6)	(803.6)
Effect of foreign currency exchange rates on cash, cash equivalents, and restricted cash	1.6	6.2
Net increase in cash, cash equivalents, and restricted cash	(332.7)	585.9
Cash, cash equivalents, and restricted cash at beginning of period	2,505.8	2,059.1
Cash, cash equivalents, and restricted cash at end of period	$ 2,173.1	$ 2,645.0