Long-Term Debt - Derivative Instruments Recognized in AOCI (Details) - Attributable to Black Knight Financial Services, Inc. [Member] - Interest Rate Swap [Member] - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain Recognized in OCE	$ 0.1	$ (3.0)	$ (24.1)	$ (21.0)
Amount of loss reclassified from Accumulated OCE into Net earnings	$ 3.9	$ 0.1	$ 8.3	$ (0.9)

Amount before tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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