Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 257.8	$ 345.0	$ 566.9
Adjustments to reconcile net income to net cash provided by operating activities:
Share-based compensation expense	190.2	202.2	217.1
Depreciation, amortization, and accretion	212.4	210.3	210.5
Operating lease assets expense	42.3	42.0	0.0
Loss on extinguishment of debt	55.0	15.3	0.0
Deferred income taxes	(52.3)	2.9	42.6
Other	(2.9)	3.5	9.6
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable, net	(76.1)	(118.1)	96.3
Prepaid expenses and other assets	(117.8)	(100.7)	(70.9)
Accounts payable	56.0	6.4	3.5
Accrued compensation	38.7	6.5	41.4
Income taxes payable	(57.2)	(40.5)	(269.2)
Other accrued liabilities	4.4	(46.8)	(11.4)
Deferred revenue	61.5	0.9	24.7
Net cash provided by operating activities	612.0	528.9	861.1
Cash flows from investing activities:
Purchases of property and equipment	(100.4)	(109.6)	(147.4)
Purchases of available-for-sale debt securities	(967.0)	(3,209.8)	(1,228.5)
Proceeds from sales of available-for-sale debt securities	360.4	1,520.0	1,070.2
Proceeds from maturities and redemptions of available-for-sale debt securities	865.0	1,642.3	910.2
Purchases of equity securities	(17.4)	(107.1)	(17.5)
Proceeds from sales of equity securities	9.7	14.2	36.9
Proceeds from Pulse note receivable	50.0	0.0	0.0
Payments for business acquisitions, net of cash and cash equivalents acquired	(438.1)	(270.9)	(16.4)
Subsequent payments related to acquisitions in prior years	(45.9)	(7.3)	(42.7)
Other	(5.2)	0.0	0.0
Net cash (used in) provided by investing activities	(288.9)	(528.2)	564.8
Cash flows from financing activities:
Repurchase and retirement of common stock	(381.1)	(554.9)	(756.6)
Proceeds from issuance of common stock	54.7	55.6	56.9
Payment of dividends	(264.1)	(260.1)	(249.3)
Payment of debt	(376.2)	(950.0)	0.0
Issuance of debt, net	792.4	495.2	0.0
Payment for debt extinguishment costs	(52.9)	(14.6)	0.0
Change in customer financing arrangement	0.0	0.0	(16.9)
Other	4.8	0.0	(2.7)
Net cash used in financing activities	(222.4)	(1,228.8)	(968.6)
Effect of foreign currency exchange rates on cash, cash equivalents, and restricted cash	5.8	(1.2)	(10.6)
Net increase in cash, cash equivalents, and restricted cash	106.5	(1,229.3)	446.7
Cash, cash equivalents, and restricted cash at beginning of period	1,383.0	1,276.5	2,505.8
Cash, cash equivalents, and restricted cash at end of period	1,276.5	2,505.8	2,059.1
Supplemental disclosures of cash flow information:
Cash paid for interest, net of amounts capitalized	87.2	90.6	94.0
Cash paid for income taxes, net	$ 84.1	$ 98.8	$ 181.0