Basis of Presentation - Reporting and Accounting Policies - Allowance for Credit Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Allowance for Credit Loss [Abstract]
Premium Receivable, Allowance for Credit Loss, Beginning Balance	$ 276.2	$ 265.3	$ 280.4	$ 356.2
Allowance acquired during period	0.0	3.5	0.0	3.5
Increase in allowance	95.8	87.4	189.7	148.3
Write-offs	(106.2)	(111.0)	(204.3)	(262.8)
Allowance for credit losses, end of period	$ 265.8	$ 245.2	$ 265.8	$ 245.2