Segment Information - Supplemental Geographic and Customer Solution Set Information (Details) - USD ($) $ in Millions	3 Months Ended					6 Months Ended			9 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020		Jun. 30, 2021	Jun. 30, 2020		Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Revenue	$ 520.9	$ 479.9	$ 444.4	$ 418.7	[1]	$ 1,025.4	$ 814.4	[1]	$ 1,258.8	$ 1,738.7
Finance & Risk
Segment Reporting Information [Line Items]
Revenue	303.8			247.6		599.3	489.1
Sales & Marketing
Segment Reporting Information [Line Items]
Revenue	217.1			171.1		426.1	325.3
Operating Segments | North America
Segment Reporting Information [Line Items]
Revenue	357.2			354.4		696.6	695.9
Operating Segments | North America | Finance & Risk
Segment Reporting Information [Line Items]
Revenue	199.7			193.8		390.2	386.6
Operating Segments | North America | Sales & Marketing
Segment Reporting Information [Line Items]
Revenue	157.5			160.6		306.4	309.3
Operating Segments | International
Segment Reporting Information [Line Items]
Revenue	163.7			66.4		333.6	138.0
Operating Segments | International | Finance & Risk
Segment Reporting Information [Line Items]
Revenue	104.1			54.1		211.4	112.7
Operating Segments | International | Sales & Marketing
Segment Reporting Information [Line Items]
Revenue	59.6			12.3		122.2	25.3
Corporate and other
Segment Reporting Information [Line Items]
Revenue	0.0			(2.1)		(4.8)	(19.5)
Corporate and other | Finance & Risk
Segment Reporting Information [Line Items]
Revenue	0.0			(0.3)		(2.3)	(10.2)
Corporate and other | Sales & Marketing
Segment Reporting Information [Line Items]
Revenue	$ 0.0			$ (1.8)		$ (2.5)	$ (9.3)

[1] See discussion in Note 1 - Basis of Presentation for further detail regarding the elimination of the International lag reporting.