Accumulated Other Comprehensive Income (Loss) - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended						6 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020		Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2020
Reclassifications out of AOCI [Line Items]
Other Income (Expense)- Net	$ 6.8				$ 89.3	[1]
Interest Expense	48.9				83.0	[1]
Tax benefit (expense)	9.8	$ 1.4	$ 9.1	$ 27.7	74.2	[1]	$ 101.9	$ 111.0	$ 112.4
Net income (loss)	(23.3)				74.3	[2]
Reclassification out of Accumulated Other Comprehensive Income
Reclassifications out of AOCI [Line Items]
Interest Expense	0.8				0.5
Total before tax	1.2				0.4
Tax benefit (expense)	0.0				(0.1)
Net income (loss)	1.2				0.3
Net income (loss) attributable to Dun & Bradstreet Holdings, Inc.	1.2				0.3
Amortization of prior service costs | Reclassification out of Accumulated Other Comprehensive Income
Reclassifications out of AOCI [Line Items]
Other Income (Expense)- Net	0.4				(0.1)
Amortization of actuarial gain/loss | Reclassification out of Accumulated Other Comprehensive Income
Reclassifications out of AOCI [Line Items]
Other Income (Expense)- Net	$ 0.0				$ 0.0

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

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