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, 2023	Dec. 31, 2022	Jun. 30, 2022	Dec. 31, 2021
Supplemental Cash Flow Elements [Abstract]
Restricted fiduciary cash	$ 1,398.5	$ 1,231.9
Non-restricted fiduciary cash	237.0	151.3
Total restricted and non-restricted fiduciary cash at the end of the period	1,635.5	1,383.2
Cash and cash equivalents	627.9	650.0	$ 2,383.5
Fiduciary cash	1,635.5		904.0
Total cash, cash equivalents and fiduciary cash at the end of the period	$ 2,263.4	$ 2,033.2	$ 3,287.5	$ 1,470.2