Deposit Asset on Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Apr. 01, 2019
Effects of Reinsurance [Line Items]
Reinsurance block of in-force fixed and variable annuity business			$ 2,900.0
Reinsured percentage of total in force fixed annuity account balances			50.00%
Fixed annuity reserves reinsured on a coinsurance basis							$ 2,200.0
Separate account asset	$ 3,256.7			$ 3,256.7		$ 2,891.4
Separate account liability	3,256.7			3,256.7		$ 2,891.4
Net investment income	109.2	$ 80.4		204.7	$ 162.7
Deposit asset on reinsurance
Effects of Reinsurance [Line Items]
Net investment income	25.1	$ 23.9		49.5	$ 47.6
Reinsurance Contract Modified Coinsurance Basis
Effects of Reinsurance [Line Items]
Separate account asset	700.0			700.0
Separate account liability	$ 700.0			$ 700.0
Minimum
Effects of Reinsurance [Line Items]
Minimum crediting rating			4.50%