Nature of Business and Summary of Significant Accounting Policies - Accounts Receivable and Allowances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Receivables Sold and Derecognized	$ 3,824.5	$ 1,846.8
Proceeds Collected on Behalf of Financial Institutions	3,645.9	1,639.0
Net Proceeds (Paid to) Received From Financial Institutions	(19.6)	134.1
Deferred Purchase Price	66.9	101.7
Receivables sold	119.0	64.0
Amount transferred subject to continuing involvement	$ 602.0	$ 583.0