CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities:
Net income	$ 601.8	$ 526.6
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization	123.7	108.2
Depreciation	30.5	28.3
Non-cash stock-based compensation	67.0	50.3
Change in estimated acquisition earn-out payables	29.4	(33.1)
Deferred income taxes	(1.4)	40.2
Amortization of debt discount and disposal of deferred financing costs	3.1	2.8
Amortization (accretion) of discounts and premiums, investment	0.1	0.2
Net (gain)/loss on sales/disposals of investments, fixed assets and customer accounts	(11.2)
Payments on acquisition earn-outs in excess of original estimated payables	(17.7)	(24.3)
Effect of changes in foreign exchange rate changes	0.1	(0.4)
Changes in operating assets and liabilities, net of effect from acquisitions and divestitures:
Commissions, fees and other receivables (increase) decrease	(82.8)	(47.4)
Reinsurance recoverable (increase) decrease	610.9	(958.5)
Prepaid reinsurance premiums (increase) decrease	(109.5)	(17.7)
Other assets (increase) decrease	(87.1)	(15.1)
Losses and loss adjustment reserve increase (decrease)	(609.4)	970.4
Unearned premiums increase (decrease)	118.5	38.5
Accounts payable increase (decrease)	163.0	80.3
Accrued expenses and other liabilities increase (decrease)	(40.6)	(63.4)
Other liabilities increase (decrease)	(84.3)	(86.1)
Net cash provided by operating activities	704.1	599.8
Cash flows from investing activities:
Additions to fixed assets	(38.4)	(32.4)
Payments for businesses acquired, net of cash acquired	(163.3)	(1,889.7)
Proceeds from sales of fixed assets and customer accounts	8.6	2.2
Purchases of investments	(6.2)
Proceeds from sales of investments	6.0	7.3
Net cash used in investing activities	(193.3)	(1,912.6)
Cash flows from financing activities:
Fiduciary receivables and liabilities, net	117.0	24.4
Deferred acquisition purchase payment		(5.1)
Payments on acquisition earn-outs	(56.8)	(52.8)
Proceeds from long-term debt		2,000.0
Payments on long-term debt	(238.1)	(44.4)
Deferred debt issuance costs		(23.3)
Borrowings on revolving credit facility	170.0	350.0
Payments on revolving credit facilities	(170.0)	(200.0)
Issuances of common stock for employee stock benefit plans	40.6	37.4
Repurchase shares to fund tax withholdings for non-cash stock-based compensation	(39.8)	(48.7)
Purchase of treasury stock	(0.1)	(74.1)
Cash dividends paid	(97.9)	(86.9)
Net cash (used in)/provided by financing activities	(275.1)	1,876.5
Effect of foreign exchange rate changes on cash and cash equivalents inclusive of fiduciary cash	2.0	(183.1)
Net increase in cash and cash equivalents inclusive of fiduciary cash	237.7	380.6
Cash and cash equivalents inclusive of fiduciary cash at beginning of period	2,033.2	1,470.2
Cash and cash equivalents inclusive of fiduciary cash at end of period	$ 2,270.9	$ 1,850.8