Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net income	$ 108.8	$ 91.4
Adjustments to reconcile net income to net cash provided by operating activities:
Share-based compensation expense	62.0	51.8
Depreciation, amortization, and accretion	55.8	47.0
Deferred income taxes	15.3	21.1
(Gain) loss on investments and fixed assets, net	(1.0)	5.4
Changes in operating assets and liabilities, net of effects from acquisitions:
Accounts receivable, net	383.0	(3.2)
Prepaid expenses and other assets	(3.5)	(59.6)
Accounts payable	(18.4)	69.8
Accrued compensation	(47.2)	(89.3)
Income taxes payable	4.1	(24.2)
Other accrued liabilities	(25.5)	(29.8)
Deferred revenue	11.9	92.0
Net cash provided by operating activities	545.3	172.4
Cash flows from investing activities:
Purchases of property and equipment	(32.1)	(49.3)
Purchases of available-for-sale investments	(378.9)	(360.7)
Proceeds from sales of available-for-sale investments	218.8	286.2
Proceeds from maturities and redemptions of available-for-sale investments	184.3	79.6
Purchases of trading investments	(1.8)	(2.5)
Purchases of privately-held investments	0.0	(10.5)
Net cash used in investing activities	(9.7)	(57.2)
Cash flows from financing activities:
Proceeds from issuance of common stock	33.7	32.0
Purchases and retirement of common stock	(129.7)	(83.4)
Issuance of debt, net	0.0	494.0
Payment of debt	0.0	(300.0)
Payment of cash dividends	(38.0)	(38.3)
Net cash (used in) provided by financing activities	(134.0)	104.3
Effect of foreign currency exchange rates on cash and cash equivalents	7.2	5.6
Net increase in cash and cash equivalents	408.8	225.1
Cash and cash equivalents at beginning of period	1,833.2	1,420.9
Cash and cash equivalents at end of period	$ 2,242.0	$ 1,646.0