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	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Supplemental Cash Flow Elements [Abstract]
Restricted fiduciary cash	$ 572.5	$ 583.2
Non-restricted fiduciary cash	159.1	193.8
Total restricted and non-restricted fiduciary cash at the end of the period	731.6	777.0
Cash and cash equivalents	1,694.5	693.2	$ 511.7
Fiduciary cash	731.6		629.0
Total cash, cash equivalents and fiduciary cash at the end of the period	$ 2,426.1	$ 1,470.2	$ 1,140.7	$ 1,271.9