Segment Information - Summary of Financial Information Concerning Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues from external customers	$ 173.0	$ 262.3
Interest, investment and other income, including realized and other gains and losses, net	917.3	12.6
Total revenues and other income	1,090.3	274.9
Depreciation and amortization	8.4	10.4
Interest expense	(3.8)	(3.7)
(Loss) earnings before income taxes and equity in earnings (losses) of unconsolidated affiliates	860.2	(2.2)
Income tax (benefit) expense	169.4	(6.0)
Earnings before equity in losses of unconsolidated affiliates	690.8	3.8
Equity in (losses) earnings of unconsolidated affiliates	(52.7)	(21.4)
Earnings (loss) from continuing operations	638.1	(17.6)
Assets	2,705.1	1,957.8	$ 2,092.2
Goodwill	53.5	76.5	66.1
Dun & Bradstreet Elimination
Segment Reporting Information [Line Items]
Revenues from external customers	(395.3)	(174.1)
Interest, investment and other income, including realized and other gains and losses, net	(90.3)	(5.4)
Total revenues and other income	(485.6)	(179.5)
Depreciation and amortization	(134.3)	(80.5)
Interest expense	83.0	49.1
(Loss) earnings before income taxes and equity in earnings (losses) of unconsolidated affiliates	1.0	111.6
Income tax (benefit) expense	74.3	30.4
Earnings before equity in losses of unconsolidated affiliates	(73.3)	81.2
Equity in (losses) earnings of unconsolidated affiliates	9.5	(24.4)
Earnings (loss) from continuing operations	(63.8)	56.8
Assets	(9,172.4)	(9,161.0)
Goodwill	(2,850.8)	(2,797.6)
Restaurant revenue
Segment Reporting Information [Line Items]
Revenues from external customers	169.9	257.8
Restaurant revenue | Dun & Bradstreet Elimination
Segment Reporting Information [Line Items]
Revenues from external customers	0.0	0.0
Other operating revenue
Segment Reporting Information [Line Items]
Revenues from external customers	3.1	4.5
Other operating revenue | Dun & Bradstreet Elimination
Segment Reporting Information [Line Items]
Revenues from external customers	(395.3)	(174.1)
Restaurant Group
Segment Reporting Information [Line Items]
Revenues from external customers	169.9	257.8
Goodwill	53.5		66.1
Restaurant Group | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	169.9	257.8
Interest, investment and other income, including realized and other gains and losses, net	7.8	0.7
Total revenues and other income	177.7	258.5
Depreciation and amortization	7.7	9.7
Interest expense	(3.1)	(1.0)
(Loss) earnings before income taxes and equity in earnings (losses) of unconsolidated affiliates	(20.9)	(8.1)
Income tax (benefit) expense	0.0	(0.1)
Earnings before equity in losses of unconsolidated affiliates	(20.9)	(8.0)
Equity in (losses) earnings of unconsolidated affiliates	(5.2)	0.0
Earnings (loss) from continuing operations	(26.1)	(8.0)
Assets	419.7	670.7
Goodwill	53.5	76.5
Restaurant Group | Restaurant revenue
Segment Reporting Information [Line Items]
Revenues from external customers	167.0	245.3
Restaurant Group | Restaurant revenue | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	169.9	257.8
Restaurant Group | Other operating revenue | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	0.0	0.0
Dun & Bradstreet | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	395.3	174.1
Interest, investment and other income, including realized and other gains and losses, net	90.3	5.4
Total revenues and other income	485.6	179.5
Depreciation and amortization	134.3	80.5
Interest expense	(83.0)	(49.1)
(Loss) earnings before income taxes and equity in earnings (losses) of unconsolidated affiliates	(1.0)	(111.6)
Income tax (benefit) expense	(74.3)	(30.4)
Earnings before equity in losses of unconsolidated affiliates	73.3	(81.2)
Equity in (losses) earnings of unconsolidated affiliates	0.6	0.1
Earnings (loss) from continuing operations	73.9	(81.1)
Assets		9,161.0
Goodwill	2,850.8	2,797.6
Dun & Bradstreet | Restaurant revenue | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	0.0	0.0
Dun & Bradstreet | Other operating revenue | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	395.3	174.1
Corporate and Other
Segment Reporting Information [Line Items]
Goodwill	0.0		$ 0.0
Corporate and Other | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	3.1	4.5
Interest, investment and other income, including realized and other gains and losses, net	909.5	11.9
Total revenues and other income	912.6	16.4
Depreciation and amortization	0.7	0.7
Interest expense	(0.7)	(2.7)
(Loss) earnings before income taxes and equity in earnings (losses) of unconsolidated affiliates	881.1	5.9
Income tax (benefit) expense	169.4	(5.9)
Earnings before equity in losses of unconsolidated affiliates	711.7	11.8
Equity in (losses) earnings of unconsolidated affiliates	(57.6)	2.9
Earnings (loss) from continuing operations	654.1	14.7
Assets	2,285.4	1,287.1
Goodwill	0.0	0.0
Corporate and Other | Restaurant revenue | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	0.0	0.0
Corporate and Other | Other operating revenue | Operating Segments
Segment Reporting Information [Line Items]
Revenues from external customers	$ 3.1	$ 4.5