Accumulated Other Comprehensive Income (Loss) - Reclassifications (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended								12 Months Ended
	Feb. 07, 2019		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018
Reclassifications out of AOCI [Line Items]
Other Income (Expense)- Net	$ (86.0)	[1]									$ (12.0)	$ (154.8)	[1]	$ (3.3)
Interest Expense	5.5	[1]									271.1	303.5	[1]	54.4
Tax benefit (expense)	27.5	[1]									110.5	118.2	[1]	(81.6)
Total after tax	(74.8)	[1]	$ 8.3	$ (14.9)	$ (173.8)	$ 73.9	$ (228.1)	$ (55.3)	$ (60.5)	$ (209.6)	(106.5)	(553.5)	[1]	294.3
Reclassification out of Accumulated Other Comprehensive Income
Reclassifications out of AOCI [Line Items]
Interest Expense	0.0										2.8	0.7		0.9
Total before tax	3.8										2.4	0.7		41.8
Tax benefit (expense)	(1.0)										(0.6)	(0.2)		(9.4)
Total after tax	2.8										1.8	0.5		32.4
Net income (loss) attributable to Dun & Bradstreet Holdings, Inc. (Successor) / The Dun & Bradstreet Corporation (Predecessor)	2.8										1.8	0.5		32.4
Amortization of prior service costs | Reclassification out of Accumulated Other Comprehensive Income
Reclassifications out of AOCI [Line Items]
Other Income (Expense)- Net	(0.1)										(0.4)	0.0		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		$ 40.9

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