Supplementary Data Accrued Liabilities (Details) - USD ($)	9 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Accrued Liabilities [Abstract]
Salaries, benefits and related expenses	$ 372,900,000	$ 507,500,000
Income Taxes payable	0.0	56,800,000
Interest	39,000,000.0	40,200,000
Office and related expenses	17,300,000	22,300,000
Acquisition obligations	4,900,000	2,900,000
Restructuring charges	200,000	600,000
Other	69,300,000	75,500,000
Total Accrued Liabilities	503,600,000	$ 705,800,000
Valuation Allowance for Impairment of Recognized Servicing Assets, Sales and Disposals	$ (15,400,000)