Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net income	$ 185.8	$ 32.9	$ 536.5	$ 317.7
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of fixed assets	49.4	45.8	141.3	138.0
Amortization of intangible assets	41.5	33.3	123.6	100.1
Amortization of debt issuance costs and original issue discount, net of original issue premium	0.5	1.6	1.3	3.5
Provision for doubtful accounts	1.4	1.8	6.8	5.1
Loss (gain) on sale of assets	0.0	6.2	(19.4)	6.2
Stock-based compensation	10.0	8.8	39.1	36.4
Realized gain on available-for-sale securities, net	0.0	(0.1)	0.0	(0.7)
Deferred income taxes	12.4	(27.4)	10.9	(27.4)
Loss on disposal of fixed assets, net	0.1	0.0	0.5	0.0
Changes in assets and liabilities, net of effects from acquisitions:
Accounts receivable	26.8	35.2	(3.6)	(54.5)
Prepaid expenses and other assets	(8.3)	(9.2)	(62.1)	(19.9)
Operating lease right-of-use assets, net	9.3	9.9	28.6	28.5
Income taxes	(63.3)	2.7	3.3	13.9
Acquisition-related liabilities	(0.1)	44.9	(63.4)	40.5
Accounts payable and accrued liabilities	39.3	138.7	(12.1)	152.7
Deferred revenues	(90.5)	(95.3)	94.3	71.5
Operating lease liabilities	(8.7)	(8.7)	(16.6)	(27.2)
Other liabilities	1.5	(7.5)	10.2	(4.5)
Net cash provided by operating activities	207.1	213.6	819.2	779.9
Cash flows from investing activities:
Acquisitions, net of cash acquired of $5.2 and $3.1 and $5.2 and $6.8, respectively	(151.9)	(40.4)	(151.9)	(109.5)
Escrow funding associated with acquisitions	(8.0)	(4.5)	(8.0)	(4.5)
Proceeds from sale of assets	0.0	0.0	23.1	0.0
Purchase of investments in a nonpublic company	0.0	0.0	(63.8)	0.0
Capital expenditures	(64.8)	(60.7)	(174.4)	(152.8)
Other investing activities, net	5.7	(0.8)	10.3	(7.7)
Net cash used in investing activities	(219.0)	(106.4)	(364.7)	(274.5)
Cash flows from financing activities:
Repayments of short-term debt, net	0.0	(60.0)	(495.0)	(405.0)
Proceeds from issuance of short-term debt with original maturities greater than three months	0.0	0.0	20.0	0.0
Repayments of short-term debt with original maturities greater than three months	0.0	0.0	(20.0)	0.0
Repayments of current portion of long-term debt	0.0	0.0	0.0	(250.0)
Proceeds from issuance of long-term debt, inclusive of original issue premium and net of original issue discount	0.0	221.8	494.8	619.7
Payment of debt issuance costs	(0.1)	(1.2)	(5.7)	(5.3)
Repurchases of common stock	(50.0)	(75.0)	(298.8)	(200.0)
Proceeds from stock options exercised	26.0	13.5	68.3	45.8
Net share settlement from restricted stock awards	0.0	0.0	(3.5)	(5.1)
Dividends paid	(43.9)	(40.8)	(131.8)	(122.7)
Payment of contingent liability related to acquisitions	0.0	0.0	(34.2)	0.0
Other financing activities, net	(8.5)	(6.9)	(13.0)	(12.2)
Net cash (used in) provided by financing activities	(76.5)	51.4	(418.9)	(334.8)
Effect of exchange rate changes	0.8	(0.1)	1.3	1.7
(Decrease) increase in cash and cash equivalents	(87.6)	158.5	36.9	172.3
Cash and cash equivalents classified within current assets held for sale, beginning of period	0.0	0.0	0.3	0.0
Cash and cash equivalents, beginning of period	309.4	153.3	184.6	139.5
Cash and cash equivalents, end of period	221.8	311.8	221.8	311.8
Supplemental disclosures:
Income taxes paid	107.1	37.5	132.8	98.9
Interest paid	19.2	16.5	82.9	77.1
Noncash investing and financing activities:
Debt issuance costs included in accounts payable and accrued liabilities	0.1	1.3	0.0	1.3
Deferred tax liability established on date of acquisition	1.8	2.9	1.8	2.8
Right-of-use assets obtained in exchange for new operating lease liabilities	0.0	0.0	0.0	247.6
Finance lease obligations	23.8	9.8	25.4	19.2
Operating lease additions, net of terminations	2.3	2.0	47.5	3.3
Tenant improvements included in Operating lease right-of-use assets, net	0.1	0.9	0.1	1.6
Fixed assets included in accounts payable and accrued liabilities	1.1	0.5	1.1	0.5
Dividend payable included in other liabilities	0.1	0.8	0.5	1.0
Gain on sale of assets included in other current and long-term assets	0.0	0.0	3.5	0.0
Held for sale assets contributed to a nonpublic company	$ 0.0	$ 0.0	$ 65.9	$ 0.0