Business and Basis of Presentation Business and Basis of Presentation (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) Company	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Company	Sep. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Number of holding companies with outstanding public debt | Company	2		2
Fixed maturity securities	$ 9,414.0		$ 9,414.0			$ 10,122.0
Amortized cost	8,938.0		8,938.0			9,639.0
Allowance for credit loss	76.0	$ 191.0	76.0	$ 191.0	$ 75.0	0.0	$ 191.0	$ 185.0
Credit loss expense	0.0	$ 0.0	1.0	$ 0.0
Cumulative Effect, Period of Adoption, Adjustment
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Allowance for credit loss					$ 0.0	62.0	$ 0.0	$ 0.0
PCD Accounting Model to PCI Securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Credit loss expense	0.1		14.0
Accretion	$ 1.0		$ 3.0
PCD Accounting Model to PCI Securities | Cumulative Effect, Period of Adoption, Adjustment
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Fixed maturity securities						248.0
Amortized cost						266.0
Allowance for credit loss						$ 62.0