Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Assets:
Settlement assets	$ 3,480.8	$ 3,486.8
Cash and cash equivalents	1,138.2	1,285.9	$ 1,176.1
Derivatives	30.1	126.1
Liabilities:
Derivatives	5.5	98.9
Recurring
Assets:
Derivatives	30.1	126.1
Total assets	1,419.8	1,471.5
Liabilities:
Derivatives	5.5	98.9
Total liabilities	5.5	98.9
Recurring | Money market funds
Assets:
Settlement assets	6.4	11.7
Recurring | State and municipal debt securities
Assets:
Settlement assets	981.0	933.3
Recurring | United States government agency mortgage-backed securities
Assets:
Settlement assets	13.6	20.5
Recurring | Corporate debt securities
Assets:
Settlement assets	152.9	146.9
Recurring | State and municipal variable-rate demand notes
Assets:
Settlement assets	48.3	48.9
Recurring | Asset-backed securities
Assets:
Settlement assets	187.5	184.1
Recurring | Level 1
Assets:
Total assets	6.4	11.7
Recurring | Level 1 | Money market funds
Assets:
Settlement assets	6.4	11.7
Recurring | Level 2
Assets:
Derivatives	30.1	126.1
Total assets	1,413.4	1,459.8
Liabilities:
Derivatives	5.5	98.9
Total liabilities	5.5	98.9
Recurring | Level 2 | State and municipal debt securities
Assets:
Settlement assets	981.0	933.3
Recurring | Level 2 | United States government agency mortgage-backed securities
Assets:
Settlement assets	13.6	20.5
Recurring | Level 2 | Corporate debt securities
Assets:
Settlement assets	152.9	146.9
Recurring | Level 2 | State and municipal variable-rate demand notes
Assets:
Settlement assets	48.3	48.9
Recurring | Level 2 | Asset-backed securities
Assets:
Settlement assets	$ 187.5	$ 184.1