CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Cash flows from operating activities:
Net income	$ 526.6	$ 485.4
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization	108.2	88.6
Depreciation	28.3	25.4
Non-cash stock-based compensation	50.3	46.7
Change in estimated acquisition earn-out payables	(33.1)	20.6
Deferred income taxes	40.2	25.4
Amortization of debt discount and disposal of deferred financing costs	2.8	2.1
Amortization (accretion) of discounts and premiums, investment	0.2	0.1
Net (gain)/loss on sales/disposals of investments, fixed assets and customer accounts		(2.0)
Payments on acquisition earn-outs in excess of original estimated payables	(24.3)	(5.7)
Effect of changes in foreign exchange rate changes	(0.4)	0.5
Changes in operating assets and liabilities, net of effect from acquisitions and divestitures:
Commissions, fees and other receivables (increase) decrease	(47.4)	(75.8)
Reinsurance recoverable (increase) decrease	(958.5)	(177.0)
Prepaid reinsurance premiums (increase) decrease	(17.7)	(33.6)
Other assets (increase) decrease	(15.1)	(6.5)
Losses and loss adjustment reserve increase (decrease)	970.4	177.0
Unearned premiums increase (decrease)	38.5	33.6
Accounts payable increase (decrease)	80.3	54.5
Accrued expenses and other liabilities increase (decrease)	(63.4)	(0.8)
Other liabilities increase (decrease)	(86.1)	(30.7)
Net cash provided by operating activities	599.8	627.8
Cash flows from investing activities:
Additions to fixed assets	(32.4)	(34.6)
Payments for businesses acquired, net of cash acquired	(1,889.7)	(178.0)
Proceeds from sales of fixed assets and customer accounts	2.2	9.3
Purchases of investments		(12.4)
Proceeds from sales of investments	7.3	9.3
Net cash used in investing activities	(1,912.6)	(206.4)
Cash flows from financing activities:
Fiduciary receivables and liabilities, net	24.4	0.1
Deferred acquisition purchase payment	(5.1)
Payments on acquisition earn-outs	(52.8)	(36.1)
Proceeds from long-term debt	2,000.0
Payments on long-term debt	(44.4)	(52.5)
Deferred debt issuance costs	(23.3)
Borrowings on revolving credit facility	350.0
Payments on revolving credit facilities	(200.0)
Issuances of common stock for employee stock benefit plans	37.4	33.8
Repurchase shares to fund tax withholdings for non-cash stock-based compensation	(48.7)	(49.6)
Purchase of treasury stock	(74.1)	(82.6)
Cash dividends paid	(86.9)	(78.2)
Net cash provided by (used in) financing activities	1,876.5	(265.1)
Effect of foreign exchange rate changes on cash and cash equivalents inclusive of fiduciary cash	(183.1)	(2.3)
Net increase in cash and cash equivalents inclusive of fiduciary cash	380.6	154.0
Cash and cash equivalents inclusive of fiduciary cash at beginning of period	1,470.2	1,271.9
Cash and cash equivalents inclusive of fiduciary cash at end of period	$ 1,850.8	$ 1,425.9