Goodwill and Other Intangibles - Other Intangibles (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Feb. 07, 2019	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019
Finite-lived Intangible Assets [Roll Forward]
Amortization	$ (3.2)	$ (113.4)	$ (113.5)	$ (116.1)	$ (108.8)	$ (121.0)	$ (70.7)
Total
Balance at beginning of period	0.0	5,022.3	5,143.4	5,251.4	5,361.3	5,488.1	0.0
Acquisition				9.2	12.9		5,558.8
Additions	0.1	0.3	0.2	0.1	0.3	0.2
Amortization	(3.2)	(113.4)	(113.5)	(116.1)	(108.8)	(121.0)	(70.7)
Other	0.1	16.1	(7.8)	(1.2)	(11.7)	(6.0)
Balance at end of period	281.1	4,925.3	5,022.3	5,143.4	5,254.0	5,361.3	5,488.1
Dun & Bradstreet Corp
Total
Balance at beginning of period	284.1						284.1
Other Indefinite-Lived Intangibles
Indefinite-lived Intangible Assets [Roll Forward]
Balance at beginning of period	0.0	1,275.8	1,275.8	1,275.8	1,200.8	1,200.8	0.0
Acquisition				0.0	53.0		1,200.8
Additions	0.0	0.0	0.0	0.0	0.0	0.0
Other	0.0	0.0	0.0	0.0	0.0	0.0
Balance at end of period	158.4	1,275.8	1,275.8	1,275.8	1,253.8	1,200.8	1,200.8
Other Indefinite-Lived Intangibles | Dun & Bradstreet Corp
Indefinite-lived Intangible Assets [Roll Forward]
Balance at beginning of period	158.4						158.4
Customer Relationships
Finite-lived Intangible Assets [Roll Forward]
Balance at beginning of period	0.0	2,033.4	2,099.2	2,162.1	2,469.1	2,547.0	0.0
Additions	0.0	0.0	0.0	0.0	0.0	0.0
Acquisition				2.4	(297.9)		2,589.0
Amortization	(1.7)	(63.3)	(63.3)	(65.1)	(51.6)	(71.9)	(42.0)
Other	0.1	5.0	(2.5)	(0.2)	(1.6)	(6.0)
Balance at end of period	74.1	1,975.1	2,033.4	2,099.2	2,118.0	2,469.1	2,547.0
Total
Amortization	(1.7)	(63.3)	(63.3)	(65.1)	(51.6)	(71.9)	(42.0)
Customer Relationships | Dun & Bradstreet Corp
Finite-lived Intangible Assets [Roll Forward]
Balance at beginning of period	75.7						75.7
Database and Other
Finite-lived Intangible Assets [Roll Forward]
Balance at beginning of period	0.0	1,713.1	1,768.4	1,813.5	1,691.4	1,740.3	0.0
Additions	0.1	0.3	0.2	0.1	0.3	0.2
Acquisition				6.8	257.8		1,769.0
Amortization	(1.5)	(50.1)	(50.2)	(51.0)	(57.2)	(49.1)	(28.7)
Other	0.0	11.1	(5.3)	(1.0)	(10.1)	0.0
Balance at end of period	48.6	1,674.4	1,713.1	1,768.4	1,882.2	1,691.4	1,740.3
Total
Amortization	(1.5)	$ (50.1)	$ (50.2)	$ (51.0)	$ (57.2)	$ (49.1)	(28.7)
Database and Other | Dun & Bradstreet Corp
Finite-lived Intangible Assets [Roll Forward]
Balance at beginning of period	$ 50.0						$ 50.0