Selected Financial Information - Level 4 Tag $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) segment Segment	Jun. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Revenue	$ (634.4)	$ (661.9)	$ (1,322.0)	$ (1,281.2)
Number of Reportable Segments | Segment			3
Number of Corporate Units | segment			1
Net loss/(gain) on investments in affiliated companies and assets-held-for sale			$ 0.5	(22.6)
Business Combination, Acquisition Related Costs	1.2		3.3
Loss Contingency, Loss in Period			30.5
Reimbursement		(0.2)	(0.1)	(0.2)
Write off of Deferred Debt Issuance Cost			(0.5)
Currency remeasurement	(2.0)	(0.1)	(2.9)	(0.2)
Loan Related Fees	0.4	0.6	0.8	1.0
Loan Related Fees - Hedge Fees			0.2
EBITDA [Abstract]
Segments Adjusted EBITDA	270.4	294.1	559.5	561.3
EBITDA Adjustment - Corporate Expense	(27.7)	(30.4)	(53.5)	(58.7)
EBITDA Adjustment - Net Interest Expense	(32.3)	(43.4)	(68.1)	(86.9)
EBITDA Adjustment - Depreciation and Amortization	(90.8)	(89.2)	(181.2)	(182.7)
EBITDA Adjustment - Acquisition Related Revenue Adjustment	0.0	(1.7)	0.0	(5.9)
EBITDA Adjustment - Stockbased Compensation	(19.4)	(8.2)	(21.7)	(20.9)
EBITDA Adjustment - Mergers and Acquisition	(7.1)	(23.9)	(11.5)	(12.6)
EBITDA Adjustment - Accelerated Technology	(3.3)	0.0	(5.8)	0.0
EBITDA Adjustment - Other	(1.8)	(1.3)	(33.8)	(1.9)
Less: net income from continuing operations attributable to noncontrolling interests	(1.5)	(2.5)	(5.6)	(4.9)
EBITDA Adjustment - Total	(177.4)	(147.8)	(369.9)	(339.4)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	93.0	146.3	189.6	221.8
Other Nonoperating Expense	0.1		0.1
Write off of Deferred Debt Issuance Cost		0.8		0.8
Income (Loss) from Equity Method Investments	2.1	3.3	4.6	7.1
Acquisition-related Costs [Member]
Segment Reporting Information [Line Items]
Business Combination, Acquisition Related Costs		0.8		1.6
Fair Value, Inputs, Level 3 [Member]
Segment Reporting Information [Line Items]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings		(0.9)	0.3
UNITED KINGDOM
Segment Reporting Information [Line Items]
Net loss/(gain) on investments in affiliated companies and assets-held-for sale			(1.8)
U.S. Markets
Segment Reporting Information [Line Items]
Revenue	(405.5)	(405.9)	(827.3)	(774.7)
EBITDA [Abstract]
Segments Adjusted EBITDA	171.2	175.4	342.7	317.5
Income (Loss) from Equity Method Investments	0.6	0.6	1.3	1.3
U.S. Markets | Financial Services [Member]
Segment Reporting Information [Line Items]
Revenue	(222.2)	(213.0)	(452.6)	(402.1)
U.S. Markets | Emerging Verticals [Member]
Segment Reporting Information [Line Items]
Revenue	(183.2)	(192.9)	(374.7)	(372.6)
International
Segment Reporting Information [Line Items]
Revenue	(119.7)	(151.1)	(277.4)	(297.1)
EBITDA [Abstract]
Segments Adjusted EBITDA	37.5	59.6	97.7	124.5
Income (Loss) from Equity Method Investments	1.4	2.7	3.3	5.8
International | CANADA
Segment Reporting Information [Line Items]
Revenue	(24.1)	(25.4)	(50.6)	(48.4)
International | Latin America [Member]
Segment Reporting Information [Line Items]
Revenue	(17.2)	(26.2)	(41.5)	(51.5)
International | UNITED KINGDOM
Segment Reporting Information [Line Items]
Revenue	(39.2)	(46.6)	(88.0)	(88.8)
International | Africa [Member]
Segment Reporting Information [Line Items]
Revenue	(9.0)	(14.0)	(23.3)	(29.0)
International | INDIA
Segment Reporting Information [Line Items]
Revenue	(17.6)	(24.9)	(48.4)	(52.6)
International | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Revenue	(12.5)	(14.0)	(25.6)	(26.8)
Consumer Interactive
Segment Reporting Information [Line Items]
Revenue	(128.4)	(123.6)	(255.1)	(246.9)
EBITDA [Abstract]
Segments Adjusted EBITDA	61.7	59.1	119.1	119.3
Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenue	(653.5)	(680.5)	(1,359.9)	(1,318.7)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(19.1)	(18.6)	(37.8)	(37.5)
Intersegment Eliminations [Member] | U.S. Markets
Segment Reporting Information [Line Items]
Revenue	(17.4)	(17.2)	(34.5)	(34.7)
Intersegment Eliminations [Member] | International
Segment Reporting Information [Line Items]
Revenue	(1.2)	(1.3)	(2.5)	(2.5)
Intersegment Eliminations [Member] | Consumer Interactive
Segment Reporting Information [Line Items]
Revenue	(0.4)	(0.2)	(0.8)	(0.4)
Callcredit [Member] | Acquisition-related Costs [Member]
Segment Reporting Information [Line Items]
Business Combination, Integration Related Costs	3.6	$ 4.4	7.5	$ 8.5
Fraudulent Incident [Member]
EBITDA [Abstract]
Other Income	0.3		0.2
Other Income	$ 0.3		$ 0.2