Restructuring Charge - Restructuring Reserve and Utilization (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended				6 Months Ended
	Feb. 07, 2019	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Restructuring Reserve [Rollforward]
Balance at beginning of period	$ 0.0	$ 6.9	$ 11.1	$ 17.0	$ 0.0	$ 11.1	$ 0.0
Impact of purchase accounting					3.2
Charge taken during the period	0.1	4.6	2.0	17.4	18.5
Payments made during period	(2.1)	(4.4)	(6.2)	(11.8)	(4.7)	(10.6)	(17.2)
Reclassification related to leases pursuant to the adoption of Topic 842	(2.4)
Balance at end of period	3.2	7.1	6.9	22.6	17.0	7.1	22.6
Dun & Bradstreet Corp
Restructuring Reserve [Rollforward]
Balance at beginning of period	7.6				7.6		7.6
Severance and Termination
Restructuring Reserve [Rollforward]
Balance at beginning of period	0.0	3.5	6.3	16.3	0.0	6.3	0.0
Impact of purchase accounting					3.2
Charge taken during the period	0.1	4.2	2.0	10.7	17.1
Payments made during period	(1.6)	(3.7)	(4.8)	(11.1)	(4.0)
Reclassification related to leases pursuant to the adoption of Topic 842	0.0
Balance at end of period	3.2	4.0	3.5	15.9	16.3	4.0	15.9
Severance and Termination | Dun & Bradstreet Corp
Restructuring Reserve [Rollforward]
Balance at beginning of period	4.7				4.7		4.7
Contract Termination and Other Exit Costs
Restructuring Reserve [Rollforward]
Balance at beginning of period	0.0	3.4	4.8	0.7	0.0	4.8	0.0
Impact of purchase accounting					0.0
Charge taken during the period	0.0	0.4	0.0	6.7	1.4
Payments made during period	(0.5)	(0.7)	(1.4)	(0.7)	(0.7)
Reclassification related to leases pursuant to the adoption of Topic 842	(2.4)
Balance at end of period	0.0	$ 3.1	$ 3.4	$ 6.7	0.7	$ 3.1	6.7
Contract Termination and Other Exit Costs | Dun & Bradstreet Corp
Restructuring Reserve [Rollforward]
Balance at beginning of period	$ 2.9				$ 2.9		$ 2.9