Selected Financial Information (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Segment segment	Sep. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | Segment			3
Number of Corporate Units | segment			1
Revenue	$ (695.9)	$ (689.3)	$ (2,017.9)	$ (1,970.5)
EBITDA [Abstract]
Segments Adjusted EBITDA	301.1	311.6	860.6	872.9
EBITDA Adjustment - Corporate Expense	(31.2)	(30.7)	(84.7)	(89.4)
EBITDA Adjustment - Net Interest Expense	(26.5)	(41.3)	(94.6)	(128.2)
EBITDA Adjustment - Depreciation and Amortization	(92.2)	(88.7)	(273.4)	(271.4)
EBITDA Adjustment - Acquisition Related Revenue Adjustment	0.0	0.0	0.0	(5.9)
EBITDA Adjustment - Stockbased Compensation	(7.8)	(14.7)	(29.5)	(35.6)
EBITDA Adjustment - Mergers and Acquisition	(1.5)	(4.8)	(12.9)	(7.8)
EBITDA Adjustment - Accelerated Technology	(4.5)	0.0	(10.3)	0.0
EBITDA Adjustment - Other	(2.6)	(15.4)	(36.4)	(17.3)
Less: net (income) loss from continuing operations attributable to noncontrolling interests	(3.9)	3.4	(9.5)	(1.5)
EBITDA Adjustment - Total	(162.4)	(199.1)	(532.3)	(538.5)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	138.7	112.5	328.3	334.3
Unrealized Loss on Securities			4.8	8.6
Unrealized Gain on Securities			(2.5)	(31.2)
Net loss/(gain) on investments in affiliated companies and assets-held-for sale			0.5	(20.6)
Reimbursement		(0.2)	(0.1)	(0.4)
Legal Fees	4.2		34.7
Loan Related Fees	0.4	0.5	1.2	1.5
Currency remeasurement	0.8	1.6	2.1	1.9
Other Nonoperating Income	(0.3)		(0.3)	(0.1)
Loan Related Fees - Hedge Fees			0.2
Write off of Deferred Debt Issuance Cost			(0.5)
Write off of Deferred Debt Issuance Cost		0.7		1.5
Income (Loss) from Equity Method Investments	2.1	3.1	6.7	10.2
Fraudulent Incident [Member]
EBITDA [Abstract]
Other Income	0.9		1.1
Other Expenses		19.7		19.7
Other General and Administrative Expense		1.8		1.8
Other Income	0.9		1.1
Fraudulent Incident [Member] | Non-controlling Interest Member [Member]
EBITDA [Abstract]
Nonoperating Gains (Losses)		(7.1)		(7.1)
Fair Value, Inputs, Level 3 [Member]
EBITDA [Abstract]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings		(0.6)	(0.3)	0.6
Acquisition-related Costs [Member]
EBITDA [Abstract]
Business Combination, Acquisition Related Costs	1.5	0.5	4.8	2.1
Acquisition-related Costs [Member] | Callcredit [Member]
EBITDA [Abstract]
Business Combination, Integration Related Costs		2.0	7.5	10.5
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(19.0)	(18.7)	(56.8)	(56.2)
UNITED KINGDOM
EBITDA [Abstract]
Net loss/(gain) on investments in affiliated companies and assets-held-for sale		(2.0)	(1.8)	2.0
U.S. Markets
Segment Reporting Information [Line Items]
Revenue	(438.5)	(420.2)	(1,265.8)	(1,194.9)
EBITDA [Abstract]
Segments Adjusted EBITDA	177.3	181.0	520.0	498.5
Income (Loss) from Equity Method Investments	0.8	0.8	2.0	2.0
U.S. Markets | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(17.2)	(17.1)	(51.7)	(51.8)
International
Segment Reporting Information [Line Items]
Revenue	(144.8)	(160.0)	(422.2)	(457.1)
EBITDA [Abstract]
Segments Adjusted EBITDA	56.7	64.0	154.4	188.6
Income (Loss) from Equity Method Investments	1.4	2.4	4.7	8.2
International | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(1.4)	(1.3)	(3.9)	(3.8)
International | CANADA
Segment Reporting Information [Line Items]
Revenue	(27.9)	(27.3)	(78.5)	(75.7)
International | Latin America [Member]
Segment Reporting Information [Line Items]
Revenue	(21.7)	(26.4)	(63.2)	(77.9)
International | UNITED KINGDOM
Segment Reporting Information [Line Items]
Revenue	(44.2)	(47.6)	(132.1)	(136.4)
International | Africa [Member]
Segment Reporting Information [Line Items]
Revenue	(12.3)	(15.7)	(35.6)	(44.7)
International | INDIA
Segment Reporting Information [Line Items]
Revenue	(23.9)	(27.4)	(72.4)	(80.0)
International | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Revenue	(14.9)	(15.6)	(40.5)	(42.4)
Consumer Interactive
Segment Reporting Information [Line Items]
Revenue	(131.6)	(127.8)	(386.7)	(374.7)
EBITDA [Abstract]
Segments Adjusted EBITDA	67.1	66.5	186.2	185.8
Consumer Interactive | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(0.5)	(0.2)	(1.3)	(0.6)
Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenue	(714.9)	(708.0)	(2,074.8)	(2,026.7)
Financial Services [Member] | U.S. Markets
Segment Reporting Information [Line Items]
Revenue	(249.1)	(225.3)	(701.7)	(627.4)
Emerging Verticals [Member] | U.S. Markets
Segment Reporting Information [Line Items]
Revenue	$ (189.4)	$ (194.9)	$ (564.1)	$ (567.5)