Basis of Presentation and Description of Business - Narrative (Details) $ / shares in Units, $ in Millions																1 Months Ended	3 Months Ended		12 Months Ended
	Jul. 06, 2020 USD ($) $ / shares shares	Jun. 26, 2020 USD ($)	Jun. 23, 2020 shares	May 14, 2020 $ / shares	Mar. 27, 2020 USD ($)	Mar. 04, 2020 $ / shares	Dec. 27, 2019 USD ($)	Dec. 16, 2019 $ / shares	Sep. 27, 2019 USD ($)	Jul. 30, 2019 $ / shares	Jun. 28, 2019 USD ($)	Jun. 19, 2019 USD ($)	May 31, 2019 $ / shares	Feb. 08, 2019 USD ($) shares	Aug. 08, 2018 USD ($) shares	Feb. 07, 2019 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2021 USD ($) segment $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares		Dec. 31, 2019 USD ($)	[1]
Class of Stock [Line Items]
Shares issued in connection with IPO and private placement (shares) | shares																				108,506,312
Consideration received on transaction	$ 2,381.0													$ 1,028.4	$ 1,028.4
Syndication fee / issuance discount	$ 42.8													$ 21.6	$ 21.6
Stock issued (shares) | shares	108,506,312
Common stock, par value (USD per share) | $ / shares																			$ 0.0001	$ 0.0001
Common stock authorized (shares) | shares			2,000,000,000																2,000,000,000	2,000,000,000
Preferred stock authorized (shares) | shares			25,000,000
Stock split ratio			314,494.968
Make-whole payment for embedded derivative	$ 205.2
Liability derivatives																			$ 0.7	$ 1.9
Change in fair value of make-whole derivative liability																$ 0.0	$ 102.6	$ (69.8)	0.0	32.8	[1]	$ 172.4
Redeemable balance of cumulative preferred stock																			1,067.9
Accretion of redeemable preferred stock																			$ 36.1	3.4
Preferred stock, dividends declared (USD per share) | $ / shares				$ 30.51		$ 30.51		$ 30.51		$ 30.51			$ 30.51
Aggregate dividends paid on preferred stock		$ 32.1			$ 32.0		$ 32.0		$ 32.1		$ 10.7	$ 21.3
Number of reportable segments | segment																			2
Class A Units | Star Parent, L.P.
Class of Stock [Line Items]
Shares issued in connection with IPO and private placement (shares) | shares															206,787.3617
Consideration received on transaction															$ 2,048.4
Syndication fee / issuance discount															$ 19.5
Class B Units | Star Parent, L.P.
Class of Stock [Line Items]
Shares issued in connection with IPO and private placement (shares) | shares															6,817.7428
Class C Units | Star Parent, L.P.
Class of Stock [Line Items]
Shares issued in connection with IPO and private placement (shares) | shares															32,987.0078
Derivatives not designated as hedging instruments
Class of Stock [Line Items]
Liability derivatives																			$ 0.7	0.9
Make-Whole Derivative Liability | Make-whole derivative liability | Derivatives not designated as hedging instruments
Class of Stock [Line Items]
Liability derivatives																				$ 172.4
Series A Preferred Stock
Class of Stock [Line Items]
Stock issued (shares) | shares														1,050,000	1,050,000
Common Stock
Class of Stock [Line Items]
Stock issued (shares) | shares															314,494,968
IPO
Class of Stock [Line Items]
Stock issued (shares) | shares	90,047,612
Common stock, par value (USD per share) | $ / shares	$ 0.0001
Offering price (USD per share) | $ / shares	$ 22.00
Private Placement
Class of Stock [Line Items]
Stock issued (shares) | shares	18,458,700
Offering price (USD per share) | $ / shares	$ 21.67
Issuance price per share relative to IPO price per share (as a percent)	98.50%
Private Placement | Subsidiary of Cannae Holdings
Class of Stock [Line Items]
Consideration received on transaction	$ 200.0
Private Placement | Subsidiary of Black Knight
Class of Stock [Line Items]
Consideration received on transaction	100.0
Private Placement | Affiliate of CC Capital
Class of Stock [Line Items]
Consideration received on transaction	$ 100.0

[1] See Note 1 Basis of Presentation and Description of Business for further detail regarding the elimination of the International lag reporting