Accumulated Other Comprehensive Income (Loss) - Reclassifications (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended		9 Months Ended
		Feb. 07, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassifications out of AOCI [Line Items]
Other Income (Expense)- Net	[1]	$ (86.0)	$ (9.5)	$ 6.3	$ (42.2)	$ 18.6
Interest Expense	[1]	5.5	60.8	85.6	221.8	220.6
Tax benefit (expense)	[1]	27.5	9.3	24.0	111.1	84.1
Total after tax	[1]	(74.8)	(14.9)	(55.3)	(114.8)	(325.4)
Reclassification out of Accumulated Other Comprehensive Income
Reclassifications out of AOCI [Line Items]
Interest Expense		0.0	0.8	0.0	2.1	0.0
Total before tax		3.8	0.7	0.0	1.8	0.0
Tax benefit (expense)		(1.0)	(0.2)	0.0	(0.5)	0.0
Total after tax		2.8	0.5	0.0	1.3	0.0
Net income (loss) attributable to Dun & Bradstreet Holdings, Inc. (Successor) / The Dun & Bradstreet Corporation (Predecessor)		2.8	0.5	0.0	1.3	0.0
Amortization of prior service costs | Reclassification out of Accumulated Other Comprehensive Income
Reclassifications out of AOCI [Line Items]
Other Income (Expense)- Net		(0.1)	(0.1)	0.0	(0.3)	0.0
Amortization of actuarial gain/loss | Reclassification out of Accumulated Other Comprehensive Income
Reclassifications out of AOCI [Line Items]
Other Income (Expense)- Net		$ 3.9	$ 0.0	$ 0.0	$ 0.0	$ 0.0

[1] See Note 1 "Basis of Presentation" for further discussion.