Earnings (Loss) Per Share - Summary (Details) - USD ($) $ / shares in Units, shares in Millions, $ 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	[1]	Jun. 30, 2021	Jun. 30, 2020	[1]	Sep. 30, 2020	Dec. 31, 2020
Earnings Per Share [Abstract]
Net income (loss) attributable to Dun & Bradstreet Holdings, Inc.	$ (51.7)	$ 1.8	$ (16.3)	$ (208.0)		$ (76.7)	$ (166.1)		$ (182.4)	$ (180.6)
Weighted average number of shares outstanding - basic (shares)	428.9			314.5		428.7	314.5
Weighted average number of shares outstanding - diluted (shares)	428.9			314.5		428.7	314.5
Earnings (loss) per share of common stock:
Basic (USD per share)	$ (0.12)	$ 0	$ (0.04)	$ (0.66)		$ (0.18)	$ (0.53)		$ (0.52)	$ (0.49)
Diluted (USD per share)	$ (0.12)	$ 0	$ (0.04)	$ (0.66)		$ (0.18)	$ (0.53)		$ (0.52)	$ (0.49)

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