Supplementary Financial Information - Schedule of Other Invested Assets (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Summary of Investment Holdings [Line Items]
Measurement Alternative	$ 11.8	$ 11.8
Equity Method	41.3	43.6
Total	53.1	55.4
Common stock
Summary of Investment Holdings [Line Items]
Measurement Alternative	0.0	0.0
Equity Method	2.5	2.5
Total	2.5	2.5
Preferred stock
Summary of Investment Holdings [Line Items]
Measurement Alternative	0.0	0.0
Equity Method	12.1	15.4
Total	12.1	15.4
Fixed maturities
Summary of Investment Holdings [Line Items]
Measurement Alternative	0.5	0.5
Equity Method	0.0	0.0
Total	0.5	0.5
Other
Summary of Investment Holdings [Line Items]
Measurement Alternative	11.3	11.3
Equity Method	26.7	25.7
Total	$ 38.0	$ 37.0