Basis of Presentation - Changes to Quarterly Results: Income Statement (Details) - USD ($) $ / shares in Units, $ 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
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenue	$ 520.9	$ 479.9	$ 444.4	$ 418.7	[1]	$ 1,025.4	$ 814.4	[1]	$ 1,258.8	$ 1,738.7
Operating Income (loss)	26.9	19.6	45.5	(2.3)	[1]	35.2	(9.5)	[1]	36.0	55.6
Income (loss) before provision (benefit) for income taxes and equity in net income of affiliates	(8.5)	1.2	(24.0)	(203.0)	[1]	(42.2)	(203.6)	[1]	(227.6)	(226.4)
Provision (benefit) for income taxes	43.0	(1.4)	(9.1)	(27.7)	[1]	33.2	(101.9)	[1]	(111.0)	(112.4)
Net income (loss) attributable to Dun & Bradstreet Holdings, Inc.	$ (51.7)	$ 1.8	$ (16.3)	$ (208.0)	[1]	$ (76.7)	$ (166.1)	[1]	$ (182.4)	$ (180.6)
Basic earnings (loss) per share of common stock attributable to Dun & Bradstreet Holdings, Inc. (USD per share)	$ (0.12)	$ 0	$ (0.04)	$ (0.66)	[1]	$ (0.18)	$ (0.53)	[1]	$ (0.52)	$ (0.49)
Diluted earnings (loss) per share of common stock attributable to Dun & Bradstreet Holdings, Inc. (USD per share)	$ (0.12)	$ 0	$ (0.04)	$ (0.66)	[1]	$ (0.18)	$ (0.53)	[1]	$ (0.52)	$ (0.49)
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenue		$ 480.1	$ 442.1	$ 420.6			$ 815.9		$ 1,258.0	$ 1,738.1
Operating Income (loss)		27.5	45.2	(1.4)			(9.7)		35.5	63.0
Income (loss) before provision (benefit) for income taxes and equity in net income of affiliates		8.5	(24.9)	(201.9)			(202.9)		(227.8)	(219.3)
Provision (benefit) for income taxes		0.6	(9.3)	(27.5)			(101.8)		(111.1)	(110.5)
Net income (loss) attributable to Dun & Bradstreet Holdings, Inc.		$ 7.0	$ (17.0)	$ (207.1)			$ (165.6)		$ (182.6)	$ (175.6)
Basic earnings (loss) per share of common stock attributable to Dun & Bradstreet Holdings, Inc. (USD per share)		$ 0.02	$ (0.04)	$ (0.66)			$ (0.53)		$ (0.52)	$ (0.48)
Diluted earnings (loss) per share of common stock attributable to Dun & Bradstreet Holdings, Inc. (USD per share)		$ 0.02	$ (0.04)	$ (0.66)			$ (0.53)		$ (0.52)	$ (0.48)
Increase (Decrease)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenue		$ (0.2)	$ 2.3	$ (1.9)			$ (1.5)		$ 0.8	$ 0.6
Operating Income (loss)		(7.9)	0.3	(0.9)			0.2		0.5	(7.4)
Income (loss) before provision (benefit) for income taxes and equity in net income of affiliates		(7.3)	0.9	(1.1)			(0.7)		0.2	(7.1)
Provision (benefit) for income taxes		(2.0)	0.2	(0.2)			(0.1)		0.1	(1.9)
Net income (loss) attributable to Dun & Bradstreet Holdings, Inc.		$ (5.2)	$ 0.7	$ (0.9)			$ (0.5)		$ 0.2	$ (5.0)
Basic earnings (loss) per share of common stock attributable to Dun & Bradstreet Holdings, Inc. (USD per share)		$ (0.02)	$ 0	$ 0			$ 0		$ 0	$ (0.01)
Diluted earnings (loss) per share of common stock attributable to Dun & Bradstreet Holdings, Inc. (USD per share)		$ (0.02)	$ 0	$ 0			$ 0		$ 0	$ (0.01)

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