Related Parties (Details) $ / shares in Units, $ in Millions						1 Months Ended				3 Months Ended	6 Months Ended	12 Months Ended
	Jul. 06, 2020 USD ($) shares	Jun. 30, 2020 $ / shares shares	Jan. 01, 2020	Feb. 08, 2019 USD ($)	Aug. 08, 2018 USD ($) shares	Sep. 30, 2021	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Feb. 07, 2019 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) profitInterestUnit	Aug. 31, 2019
Related Party Transaction [Line Items]
Term of service agreement							5 years
Stock options granted during period (shares) | shares												0	8,000,000
Total compensation expense for stock options granted									$ 11.7			$ 33.3	$ 45.1	$ 11.7
Stock issued (shares) | shares	108,506,312
Exercise price of stock options granted during period (USD per share) | $ / shares												$ 0.00	$ 22.00
Gross proceeds from sale of stock	$ 2,381.0			$ 1,028.4	$ 1,028.4
Stock options
Related Party Transaction [Line Items]
Total compensation expense for stock options granted									$ 0.0	$ 20.0		$ 3.0	$ 23.0	0.0
Common Stock
Related Party Transaction [Line Items]
Stock issued (shares) | shares					314,494,968
Private Placement
Related Party Transaction [Line Items]
Stock issued (shares) | shares	18,458,700
Issuance price per share relative to IPO price per share (as a percent)	98.50%
Stock Issuance Costs | Star Parent, L.P.
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 30.0
Board of Directors Chairman & Director | Stock options
Related Party Transaction [Line Items]
Total compensation expense for stock options granted											$ 20.0
Board of Directors Chairman & Director | Class B Profit Interest Units
Related Party Transaction [Line Items]
Fees/ expenses with related party included in "Selling and Administrative Expenses"														$ 17.3
Number of profit interest units granted (shares) | profitInterestUnit														6,817.7428
Board of Directors Chairman & Director | Class C Profit Interest Units
Related Party Transaction [Line Items]
Fees/ expenses with related party included in "Selling and Administrative Expenses"														$ 37.9
Number of profit interest units granted (shares) | profitInterestUnit														15,867.8087
Board of Directors Chairman
Related Party Transaction [Line Items]
Stock options granted during period (shares) | shares		2,080,000
Board of Directors Chairman | Trasimene Capital Management, LLC
Related Party Transaction [Line Items]
Term of service agreement			3 years
Transaction fee valuation rate (as a percent)			1.00%
Board of Directors Chairman | Services Agreement with MVB Management, LLC and THL Managers VIII, LLC
Related Party Transaction [Line Items]
Fees/ expenses with related party included in "Selling and Administrative Expenses"													0.0	$ 29.1
Board of Directors Chairman | Stock Issuance Costs | Bilcar
Related Party Transaction [Line Items]
Expenses from transactions with related party	2.5
Board of Directors Chairman | Equity Commitment Fee | Cannae Holdings
Related Party Transaction [Line Items]
Expenses from transactions with related party				12.0
Board of Directors Chairman | Service Agreement, Transaction Fees | Trasimene Capital Management, LLC
Related Party Transaction [Line Items]
Expenses from transactions with related party													0.4
Director
Related Party Transaction [Line Items]
Stock options granted during period (shares) | shares		2,080,000
Director | Stock Issuance Costs | CC Star Holdings, LP
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 2.5
Affiliated Entity | Private Placement | Common Stock
Related Party Transaction [Line Items]
Stock issued (shares) | shares	18,458,700
Issuance price per share relative to IPO price per share (as a percent)	98.50%
Exercise price of stock options granted during period (USD per share) | $ / shares		$ 22.00
Affiliated Entity | Cannae Holdings | Private Placement | Common Stock
Related Party Transaction [Line Items]
Gross proceeds from sale of stock	$ 200.0
Affiliated Entity | Black Knight Inc. | Private Placement | Common Stock
Related Party Transaction [Line Items]
Gross proceeds from sale of stock	100.0
Affiliated Entity | CC Capital | Private Placement | Common Stock
Related Party Transaction [Line Items]
Gross proceeds from sale of stock	100.0
Affiliated Entity | Stock Issuance Costs | THL Managers
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 2.5
Affiliated Entity | Equity Commitment Fee | THL Managers
Related Party Transaction [Line Items]
Expenses from transactions with related party				7.5
Affiliated Entity | Products, Data and Professional Services | Black Knight Inc.
Related Party Transaction [Line Items]
Term of service agreement							5 years
Related party transaction, revenue to be recognized from transactions with related party							$ 24.0
Related party transaction, cost to be recognized from transactions with related party							$ 34.0
Revenue from related parties												4.5
Expenses from transactions with related party												1.9
Due to related parties												3.4
Affiliated Entity | Products, Data and Professional Services | Black Knight Inc. | Accounts Payable and Accrued Liabilities
Related Party Transaction [Line Items]
Due to related parties												0.9
Affiliated Entity | Products, Data and Professional Services | Black Knight Inc. | Other Noncurrent Liabilities
Related Party Transaction [Line Items]
Due to related parties												2.5
Affiliated Entity | Data License and Risk Management Solution Services | Paysafe Limited
Related Party Transaction [Line Items]
Term of service agreement						10 years
Revenue from related parties												4.5
Related party transaction, service agreement, cancellation notice term						90 days
Affiliated Entity | Data License and Risk Management Solution Services | Paysafe Limited | Accounts Receivable
Related Party Transaction [Line Items]
Due from related parties												4.1
Affiliated Entity | Consulting Service Agreement | Black Knight Inc.
Related Party Transaction [Line Items]
Expenses from transactions with related party												$ 0.1
Related party, mark-up on consulting services, percent												10.00%
Chief Operating Officer | Motive Partners | London
Related Party Transaction [Line Items]
Term of lease															5 years
Chief Operating Officer | Motive Partners | New York
Related Party Transaction [Line Items]
Term of lease														1 year
Chief Operating Officer | Due Diligence Consulting Services Fee | Motive Partners
Related Party Transaction [Line Items]
Expenses from transactions with related party				$ 0.6
Chief Operating Officer | Lease Termination Fee | Motive Partners | London
Related Party Transaction [Line Items]
Fees/ expenses with related party included in "Selling and Administrative Expenses"								$ 0.1
Chief Operating Officer | Lease Cost | Motive Partners | London
Related Party Transaction [Line Items]
Expenses from transactions with related party													$ 1.0
Chief Operating Officer | Lease Cost | Motive Partners | New York
Related Party Transaction [Line Items]
Expenses from transactions with related party														$ 0.2