Fair Value Measurements - Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) $ in Millions	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fixed-maturity securities available for sale:
Corporate debt securities	$ 33.9	$ 19.2
Total	1,480.4	19.2
Ceridian
Fixed-maturity securities available for sale:
Equity Securities:	1,279.4
CoreLogic
Fixed-maturity securities available for sale:
Equity Securities:	154.6
Black Knight, Inc.
Fixed-maturity securities available for sale:
Equity Securities:	12.5
Level 1
Fixed-maturity securities available for sale:
Corporate debt securities	0.0	0.0
Total	1,434.0	0.0
Level 1 \| Ceridian
Fixed-maturity securities available for sale:
Equity Securities:	1,279.4
Level 1 \| CoreLogic
Fixed-maturity securities available for sale:
Equity Securities:	154.6
Level 1 \| Black Knight, Inc.
Fixed-maturity securities available for sale:
Equity Securities:	0.0
Level 2
Fixed-maturity securities available for sale:
Corporate debt securities	0.0	0.0
Total	0.0	0.0
Level 2 \| Ceridian
Fixed-maturity securities available for sale:
Equity Securities:	0.0
Level 2 \| CoreLogic
Fixed-maturity securities available for sale:
Equity Securities:	0.0
Level 2 \| Black Knight, Inc.
Fixed-maturity securities available for sale:
Equity Securities:	0.0
Level 3
Fixed-maturity securities available for sale:
Corporate debt securities	33.9	19.2
Total	46.4	$ 19.2
Level 3 \| Ceridian
Fixed-maturity securities available for sale:
Equity Securities:	0.0
Level 3 \| CoreLogic
Fixed-maturity securities available for sale:
Equity Securities:	0.0
Level 3 \| Black Knight, Inc.
Fixed-maturity securities available for sale:
Equity Securities:	$ 12.5
Level 3 \| Discount Rate \| Minimum
Fixed-maturity securities available for sale:
Discount rate	0.085
Level 3 \| Discount Rate \| Maximum
Fixed-maturity securities available for sale:
Discount rate	0.175
Level 3 \| Discount Rate \| Weighted Average
Fixed-maturity securities available for sale:
Discount rate	0.126

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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