Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income	$ 34.4	$ 108.8
Adjustments to reconcile net income to net cash provided by operating activities:
Share-based compensation expense	70.4	62.0
Depreciation, amortization, and accretion	55.7	55.8
Other	1.7	(1.0)
Changes in operating assets and liabilities, net of effects from acquisitions:
Accounts receivable, net	170.8	383.0
Prepaid expenses and other assets	(11.7)	(3.5)
Accounts payable	(31.2)	(18.4)
Accrued compensation	(14.1)	(47.2)
Income taxes payable	(7.6)	4.1
Other accrued liabilities	(51.1)	(8.9)
Deferred revenue	53.8	11.9
Net cash provided by operating activities	271.1	546.6
Cash flows from investing activities:
Purchases of property and equipment	(42.2)	(32.1)
Purchases of available-for-sale debt investments	(8.1)	(378.9)
Purchases of available-for-sale debt investments	968.0	218.8
Proceeds from maturities and redemptions of available-for-sale debt investments	215.4	184.3
Purchases of trading investments	0.0	(1.8)
Purchases of equity investments	(2.0)	0.0
Proceeds from sales of equity investments	3.3	0.0
Payment of escrow balance related to prior year acquisition	(22.2)	0.0
Net cash provided by (used in) investing activities	1,112.2	(9.7)
Cash flows from financing activities:
Repurchase and retirement of common stock, including prepayment under an accelerated share repurchase program	(754.2)	(129.7)
Proceeds from issuance of common stock	29.3	33.7
Payment of dividends	(62.1)	(38.0)
Change in customer financing arrangement	(16.6)	0.0
Net cash used in financing activities	(803.6)	(134.0)
Effect of foreign currency exchange rates on cash, cash equivalents and restricted cash	6.2	7.2
Net increase in cash, cash equivalents and restricted cash	585.9	410.1
Cash, cash equivalents and restricted cash at beginning of period	2,059.1	1,880.6
Cash, cash equivalents and restricted cash at end of period	$ 2,645.0	$ 2,290.7