Derivatives - Narrative (Details) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Mar. 09, 2021 USD ($)	Dec. 31, 2020 USD ($) derivative
Derivatives
Total borrowings at par value	$ 3,015.0			$ 3,015.0			$ 3,080.0
Accumulated other comprehensive pre-tax gain (loss) to be reclassified into revenue within the next 12 months	$ (3.7)			$ (3.7)
3.600% notes due 2022
Derivatives
Total borrowings at par value							$ 500.0
Stated interest rate (as a percent)	3.60%			3.60%			3.60%
1.350% notes due 2026
Derivatives
Total borrowings at par value	$ 600.0	$ 600.0		$ 600.0		$ 600.0
Stated interest rate (as a percent)	1.35%	1.35%		1.35%
Business Solutions
Derivatives
Foreign exchange revenues	$ 87.4		$ 70.0	$ 171.9	$ 157.5
Cash Flow Hedges | Interest rate contracts | 3.600% notes due 2022
Derivatives
Number of derivative instruments held | derivative							2
Cash payment received for terminated swap agreement		$ 3.3
Deferred gain on termination of treasury locks		2.6
Gain on derivative recognized in Other income/(expense), net		$ 0.7
Cash Flow Hedges | Interest rate contracts | 3.600% notes due 2022 | Interest Rate Swap Contract 1
Derivatives
Notional amounts							$ 100.0
Cash Flow Hedges | Interest rate contracts | 3.600% notes due 2022 | Interest Rate Swap Contract 2
Derivatives
Notional amounts							150.0
Designated as hedges | Foreign currency contracts
Derivatives
Derivative policy - contract maturity period maximum				36 months
Derivative policy - targeted weighted-average maturity				1 year
Maximum remaining maturity of foreign currency derivatives				24 months
Derivative weighted-average maturity				1 year
Not designated as hedges | Foreign currency contracts | Business Solutions
Derivatives
Notional amounts	$ 8,000.0			$ 8,000.0			$ 8,000.0
Minimum | Not designated as hedges | Uncollected settlement assets and obligations
Derivatives
Foreign currency forward contracts maturity range				2 days
Maximum | Not designated as hedges | Uncollected settlement assets and obligations
Derivatives
Foreign currency forward contracts maturity range				1 month
Maximum | Not designated as hedges | Foreign currency contracts | Business Solutions
Derivatives
Foreign currency forward contracts maturity range				1 year
Maximum | Not designated as hedges | Foreign currency denominated cash and other asset and other liability positions
Derivatives
Foreign currency forward contracts maturity range				1 year