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	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Supplemental Cash Flow Elements [Abstract]
Restricted fiduciary cash	$ 664.7	$ 583.2
Non-restricted fiduciary cash	239.3	193.8
Total restricted and non-restricted fiduciary cash at the end of the period	904.0	777.0
Cash and cash equivalents	2,383.5	693.2	$ 625.4
Fiduciary cash	904.0		725.6
Total cash, cash equivalents and fiduciary cash at the end of the period	$ 3,287.5	$ 1,470.2	$ 1,351.0	$ 1,271.9