Settlement Assets and Obligations - Settlement Assets and Obligations (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Settlement assets:
Cash and cash equivalents	$ 1,002.6	$ 695.7
Receivables from agents, Business Solutions customers, and others	1,101.6	1,188.3
Less: Allowance for credit losses	(24.8)	(53.2)
Receivables from agents, Business Solutions customers, and others, net	1,076.8	1,135.1
Investment securities	1,557.4	1,990.6
Total settlement assets	3,636.8	3,821.4
Settlement obligations:
Money transfer, money order, and payment service payables	2,884.3	2,902.9
Payables to agents	752.5	918.5
Total settlement obligations	$ 3,636.8	$ 3,821.4