Segment Information - Summary of Financial Information Concerning Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues from external customers	$ 102.6	$ 272.2	$ 275.6	$ 534.5
Interest, investment and other income, including realized and other gains and losses, net	586.4	76.5	1,503.7	89.1
Total revenues and other income	689.0	348.7	1,779.3	623.6
Depreciation and amortization	7.3	9.9	15.7	20.3
Interest expense	(1.0)	(5.5)	(4.8)	(9.2)
(Loss) earnings before income taxes and equity in earnings (losses) of unconsolidated affiliates	539.7	49.6	1,399.9	47.4
Income tax (benefit) expense	131.1	7.1	300.5	1.1
(Loss) earnings before equity in earnings of unconsolidated affiliates	408.6	42.5	1,099.4	46.3
Equity in (losses) earnings of unconsolidated affiliates	57.5	(21.1)	4.8	(42.5)
Net (loss) earnings from continuing operations	466.1	21.4	1,104.2	3.8
Assets	3,788.6	1,852.2	3,788.6	1,852.2	$ 2,092.2
Goodwill	53.5	76.5	53.5	76.5	66.1
Dun & Bradstreet Elimination
Segment Reporting Information [Line Items]
Revenues from external customers	(420.6)	(398.9)	(815.9)	(573.0)
Interest, investment and other income, including realized and other gains and losses, net	122.5	(8.7)	32.2	(13.9)
Total revenues and other income	(298.1)	(407.6)	(783.7)	(586.9)
Depreciation and amortization	(132.6)	(136.8)	(266.9)	(217.3)
Interest expense	78.0	86.0	161.0	135.0
(Loss) earnings before income taxes and equity in earnings (losses) of unconsolidated affiliates	201.9	86.4	202.9	198.3
Income tax (benefit) expense	27.5	23.1	101.8	53.5
(Loss) earnings before equity in earnings of unconsolidated affiliates	174.4	63.3	101.1	144.8
Equity in (losses) earnings of unconsolidated affiliates	(56.1)	(25.6)	(46.6)	(50.0)
Net (loss) earnings from continuing operations	118.3	37.7	54.5	94.8
Assets	(8,985.1)	(9,073.3)	(8,985.1)	(9,073.3)
Goodwill	(2,848.0)	(2,792.6)	(2,848.0)	(2,792.6)
Restaurant revenue
Segment Reporting Information [Line Items]
Revenues from external customers	99.4	266.5	269.3	524.3
Restaurant revenue | Dun & Bradstreet Elimination
Segment Reporting Information [Line Items]
Revenues from external customers	0.0	0.0	0.0	0.0
Other operating revenue
Segment Reporting Information [Line Items]
Revenues from external customers	3.2	5.7	6.3	10.2
Other operating revenue | Dun & Bradstreet Elimination
Segment Reporting Information [Line Items]
Revenues from external customers	(420.6)	(398.9)	(815.9)	(573.0)
Restaurant Group
Segment Reporting Information [Line Items]
Revenues from external customers	99.4	266.5	269.3	524.3
Goodwill	53.5		53.5		66.1
Restaurant Group | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	99.4	266.5	269.3	524.3
Interest, investment and other income, including realized and other gains and losses, net	(0.1)	2.8	7.7	3.5
Total revenues and other income	99.3	269.3	277.0	527.8
Depreciation and amortization	6.6	9.4	14.3	19.1
Interest expense	(1.1)	(1.5)	(4.2)	(2.5)
(Loss) earnings before income taxes and equity in earnings (losses) of unconsolidated affiliates	(24.0)	(11.6)	(44.9)	(19.7)
Income tax (benefit) expense	0.0	0.0	0.0	(0.1)
(Loss) earnings before equity in earnings of unconsolidated affiliates	(24.0)	(11.6)	(44.9)	(19.6)
Equity in (losses) earnings of unconsolidated affiliates	(9.7)	0.0	(14.9)	0.0
Net (loss) earnings from continuing operations	(33.7)	(11.6)	(59.8)	(19.6)
Assets	408.0	636.2	408.0	636.2
Goodwill	53.5	76.5	53.5	76.5
Restaurant Group | Restaurant revenue
Segment Reporting Information [Line Items]
Revenues from external customers	99.3	247.7	266.3	493.0
Restaurant Group | Restaurant revenue | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	99.4	266.5	269.3	524.3
Restaurant Group | Other operating revenue | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	0.0	0.0	0.0	0.0
Dun & Bradstreet | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	420.6	398.9	815.9	573.0
Interest, investment and other income, including realized and other gains and losses, net	(122.5)	8.7	(32.2)	13.9
Total revenues and other income	298.1	407.6	783.7	586.9
Depreciation and amortization	132.6	136.8	266.9	217.3
Interest expense	(78.0)	(86.0)	(161.0)	(135.0)
(Loss) earnings before income taxes and equity in earnings (losses) of unconsolidated affiliates	(201.9)	(86.4)	(202.9)	(198.3)
Income tax (benefit) expense	(27.5)	(23.1)	(101.8)	(53.5)
(Loss) earnings before equity in earnings of unconsolidated affiliates	(174.4)	(63.3)	(101.1)	(144.8)
Equity in (losses) earnings of unconsolidated affiliates	0.6	2.8	1.2	2.9
Net (loss) earnings from continuing operations	(173.8)	(60.5)	(99.9)	(141.9)
Assets	8,985.1	9,073.3	8,985.1	9,073.3
Goodwill	2,848.0	2,792.6	2,848.0	2,792.6
Dun & Bradstreet | Restaurant revenue | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	0.0	0.0	0.0	0.0
Dun & Bradstreet | Other operating revenue | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	420.6	398.9	815.9	573.0
Corporate and Other
Segment Reporting Information [Line Items]
Goodwill	0.0		0.0		$ 0.0
Corporate and Other | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	3.2	5.7	6.3	10.2
Interest, investment and other income, including realized and other gains and losses, net	586.5	73.7	1,496.0	85.6
Total revenues and other income	589.7	79.4	1,502.3	95.8
Depreciation and amortization	0.7	0.5	1.4	1.2
Interest expense	0.1	(4.0)	(0.6)	(6.7)
(Loss) earnings before income taxes and equity in earnings (losses) of unconsolidated affiliates	563.7	61.2	1,444.8	67.1
Income tax (benefit) expense	131.1	7.1	300.5	1.2
(Loss) earnings before equity in earnings of unconsolidated affiliates	432.6	54.1	1,144.3	65.9
Equity in (losses) earnings of unconsolidated affiliates	122.7	1.7	65.1	4.6
Net (loss) earnings from continuing operations	555.3	55.8	1,209.4	70.5
Assets	3,380.6	1,216.0	3,380.6	1,216.0
Goodwill	0.0	0.0	0.0	0.0
Corporate and Other | Restaurant revenue | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	0.0	0.0	0.0	0.0
Corporate and Other | Other operating revenue | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	$ 3.2	$ 5.7	$ 6.3	$ 10.2