Contractual Obligations - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	8 Months Ended	12 Months Ended			35 Months Ended	60 Months Ended
	Feb. 07, 2019	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	May 31, 2020
Other Commitments [Line Items]
Unrecorded unconditional purchase obligation		$ 566.1	$ 566.1			$ 566.1
Acxiom and Ensono Agreements
Other Commitments [Line Items]
Incurred costs	$ 6.0		86.0	$ 56.0	$ 60.0
Acxiom Agreement | Minimum
Other Commitments [Line Items]
Unrecorded unconditional purchase obligation				7.0
Ensono Information Technology and Data Processing Services Arrangement
Other Commitments [Line Items]
Unrecorded unconditional purchase obligation				105.0
Cognizant Technology Solutions Agreement
Other Commitments [Line Items]
Unrecorded unconditional purchase obligation				10.0
Incurred costs	4.0		$ 33.0	35.0	37.0
Term for commercial services agreement		2 years				3 years	3 years
Written notice requirement period for termination			6 months
Termination fee		$ 4.5	$ 4.5			$ 4.5
Worldwide Network Partnership Agreements
Other Commitments [Line Items]
Unrecorded unconditional purchase obligation				359.0
Incurred costs	$ 3.0		$ 90.0	$ 23.0	$ 22.0
Worldwide Network Partnership Agreements | Minimum
Other Commitments [Line Items]
Term for commercial services agreement			5 years
Worldwide Network Partnership Agreements | Maximum
Other Commitments [Line Items]
Term for commercial services agreement			10 years