Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net income	$ 288.6	$ 231.4
Adjustments to reconcile net income to net cash provided by operating activities:
Share-based compensation expense	106.1	107.4
Depreciation, amortization, and accretion	112.1	98.6
(Gain) loss on investments and disposal of fixed assets, net	(1.8)	1.8
Changes in operating assets and liabilities, net of effects from acquisitions:
Accounts receivable, net	304.8	39.5
Prepaid expenses and other assets	46.4	(12.5)
Accounts payable	(5.1)	62.9
Accrued compensation	(20.6)	(67.2)
Income taxes payable	27.9	(23.6)
Other accrued liabilities	(33.7)	(22.3)
Deferred revenue	19.3	116.4
Net cash provided by operating activities	844.0	532.4
Cash flows from investing activities:
Purchases of property and equipment	(64.3)	(116.9)
Purchases of available-for-sale investments	(776.4)	(794.9)
Proceeds from sales of available-for-sale investments	429.1	665.8
Proceeds from maturities and redemptions of available-for-sale investments	350.4	152.8
Proceeds from Pulse note receivable	75.0	0.0
Purchases of privately-held investments	(9.8)	(10.5)
Proceeds from sales of privately-held investments	0.0	2.8
Purchases of trading investments	(2.5)	(3.2)
Payments for business acquisitions, net of cash and cash equivalents acquired	0.0	(22.8)
Changes in restricted cash	0.0	0.5
Net cash provided by (used in) investing activities	1.5	(126.4)
Cash flows from financing activities:
Purchases and retirement of common stock	(255.3)	(210.1)
Proceeds from issuance of common stock	35.5	32.2
Payment of cash dividends	(75.8)	(76.4)
Payment of debt	0.0	(300.0)
Issuance of debt, net	0.0	494.0
Payment of financing obligations	0.0	(16.4)
Net cash used in financing activities	(295.6)	(76.7)
Effect of foreign currency exchange rates on cash and cash equivalents	9.4	6.7
Net increase in cash and cash equivalents	559.3	336.0
Cash and cash equivalents at beginning of period	1,833.2	1,420.9
Cash and cash equivalents at end of period	$ 2,392.5	$ 1,756.9