Supplemental Disclosures of Cash Flow Information and Non-Cash Financing and Investing Activities - Schedule of Reconciliation of Cash and Cash Equivalents Inclusive of Restricted Cash (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021	Dec. 31, 2020
Supplemental Cash Flow Elements [Abstract]
Restricted fiduciary cash	$ 1,113.0	$ 583.2
Non-restricted fiduciary cash	158.3	193.8
Total restricted and non-restricted fiduciary cash at the end of the period	1,271.3	777.0
Cash and cash equivalents	579.5	693.2	$ 784.6
Fiduciary cash	1,271.3		641.3
Total cash, cash equivalents and fiduciary cash at the end of the period	$ 1,850.8	$ 1,470.2	$ 1,425.9	$ 1,271.9